xref: /third_party/vk-gl-cts/external/vulkan-docs/src/chapters/synchronization.txt

// Copyright 2015-2021 The Khronos Group, Inc.
//
// SPDX-License-Identifier: CC-BY-4.0

[[synchronization]]
= Synchronization and Cache Control

Synchronization of access to resources is primarily the responsibility of
the application in Vulkan.
The order of execution of commands with respect to the host and other
commands on the device has few implicit guarantees, and needs to be
explicitly specified.
Memory caches and other optimizations are also explicitly managed, requiring
that the flow of data through the system is largely under application
control.

Whilst some implicit guarantees exist between commands, five explicit
synchronization mechanisms are exposed by Vulkan:

<<synchronization-fences,Fences>>::
    Fences can: be used to communicate to the host that execution of some
    task on the device has completed.

<<synchronization-semaphores,Semaphores>>::
    Semaphores can: be used to control resource access across multiple
    queues.

<<synchronization-events,Events>>::
    Events provide a fine-grained synchronization primitive which can: be
    signaled either within a command buffer or by the host, and can: be
    waited upon within a command buffer or queried on the host.

<<synchronization-pipeline-barriers,Pipeline Barriers>>::
    Pipeline barriers also provide synchronization control within a command
    buffer, but at a single point, rather than with separate signal and wait
    operations.

<<renderpass,Render Passes>>::
    Render passes provide a useful synchronization framework for most
    rendering tasks, built upon the concepts in this chapter.
    Many cases that would otherwise need an application to use other
    synchronization primitives can: be expressed more efficiently as part of
    a render pass.


[[synchronization-dependencies]]
== Execution and Memory Dependencies

An _operation_ is an arbitrary amount of work to be executed on the host, a
device, or an external entity such as a presentation engine.
Synchronization commands introduce explicit _execution dependencies_, and
_memory dependencies_ between two sets of operations defined by the
command's two _synchronization scopes_.

[[synchronization-dependencies-scopes]]
The synchronization scopes define which other operations a synchronization
command is able to create execution dependencies with.
Any type of operation that is not in a synchronization command's
synchronization scopes will not be included in the resulting dependency.
For example, for many synchronization commands, the synchronization scopes
can: be limited to just operations executing in specific
<<synchronization-pipeline-stages,pipeline stages>>, which allows other
pipeline stages to be excluded from a dependency.
Other scoping options are possible, depending on the particular command.

[[synchronization-dependencies-execution]]
An _execution dependency_ is a guarantee that for two sets of operations,
the first set must: _happen-before_ the second set.
If an operation happens-before another operation, then the first operation
must: complete before the second operation is initiated.
More precisely:

  * Let *A* and *B* be separate sets of operations.
  * Let *S* be a synchronization command.
  * Let *A~S~* and *B~S~* be the synchronization scopes of *S*.
  * Let *A'* be the intersection of sets *A* and *A~S~*.
  * Let *B'* be the intersection of sets *B* and *B~S~*.
  * Submitting *A*, *S* and *B* for execution, in that order, will result in
    execution dependency *E* between *A'* and *B'*.
  * Execution dependency *E* guarantees that *A'* happens-before *B'*.

[[synchronization-dependencies-chains]]
An _execution dependency chain_ is a sequence of execution dependencies that
form a happens-before relation between the first dependency's *A'* and the
final dependency's *B'*.
For each consecutive pair of execution dependencies, a chain exists if the
intersection of *B~S~* in the first dependency and *A~S~* in the second
dependency is not an empty set.
The formation of a single execution dependency from an execution dependency
chain can be described by substituting the following in the description of
execution dependencies:

  * Let *S* be a set of synchronization commands that generate an execution
    dependency chain.
  * Let *A~S~* be the first synchronization scope of the first command in
    *S*.
  * Let *B~S~* be the second synchronization scope of the last command in
    *S*.

Execution dependencies alone are not sufficient to guarantee that values
resulting from writes in one set of operations can: be read from another set
of operations.

[[synchronization-dependencies-available-and-visible]]
Three additional types of operations are used to control memory access.
_Availability operations_ cause the values generated by specified memory
write accesses to become _available_ to a memory domain for future access.
Any available value remains available until a subsequent write to the same
memory location occurs (whether it is made available or not) or the memory
is freed.
_Memory domain operations_ cause writes that are available to a source
memory domain to become available to a destination memory domain (an example
of this is making writes available to the host domain available to the
device domain).
_Visibility operations_ cause values available to a memory domain to become
_visible_ to specified memory accesses.

ifdef::VK_VERSION_1_2,VK_KHR_vulkan_memory_model[]
Availability, visibility, memory domains, and memory domain operations are
formally defined in the <<memory-model-availability-visibility,Availability
and Visibility>> section of the <<memory-model,Memory Model>> chapter.
Which API operations perform each of these operations is defined in
<<memory-model-vulkan-availability-visibility,Availability, Visibility, and
Domain Operations>>.
endif::VK_VERSION_1_2,VK_KHR_vulkan_memory_model[]

[[synchronization-dependencies-memory]]
A _memory dependency_ is an execution dependency which includes availability
and visibility operations such that:

  * The first set of operations happens-before the availability operation.
  * The availability operation happens-before the visibility operation.
  * The visibility operation happens-before the second set of operations.

Once written values are made visible to a particular type of memory access,
they can: be read or written by that type of memory access.
Most synchronization commands in Vulkan define a memory dependency.

[[synchronization-dependencies-access-scopes]]
The specific memory accesses that are made available and visible are defined
by the _access scopes_ of a memory dependency.
Any type of access that is in a memory dependency's first access scope and
occurs in *A'* is made available.
Any type of access that is in a memory dependency's second access scope and
occurs in *B'* has any available writes made visible to it.
Any type of operation that is not in a synchronization command's access
scopes will not be included in the resulting dependency.

A memory dependency enforces availability and visibility of memory accesses
and execution order between two sets of operations.
Adding to the description of <<synchronization-dependencies-chains,
execution dependency chains>>:

  * Let *a* be the set of memory accesses performed by *A'*.
  * Let *b* be the set of memory accesses performed by *B'*.
  * Let *a~S~* be the first access scope of the first command in *S*.
  * Let *b~S~* be the second access scope of the last command in *S*.
  * Let *a'* be the intersection of sets *a* and *a~S~*.
  * Let *b'* be the intersection of sets *b* and *b~S~*.
  * Submitting *A*, *S* and *B* for execution, in that order, will result in
    a memory dependency *m* between *A'* and *B'*.
  * Memory dependency *m* guarantees that:
  ** Memory writes in *a'* are made available.
  ** Available memory writes, including those from *a'*, are made visible to
     *b'*.

[NOTE]
.Note
====
Execution and memory dependencies are used to solve data hazards, i.e. to
ensure that read and write operations occur in a well-defined order.
Write-after-read hazards can be solved with just an execution dependency,
but read-after-write and write-after-write hazards need appropriate memory
dependencies to be included between them.
If an application does not include dependencies to solve these hazards, the
results and execution orders of memory accesses are undefined:.
====


[[synchronization-image-layout-transitions]]
=== Image Layout Transitions

Image subresources can: be transitioned from one <<resources-image-layouts,
layout>> to another as part of a <<synchronization-dependencies-memory,
memory dependency>> (e.g. by using an
<<synchronization-image-memory-barriers,image memory barrier>>).
When a layout transition is specified in a memory dependency, it
happens-after the availability operations in the memory dependency, and
happens-before the visibility operations.
Image layout transitions may: perform read and write accesses on all memory
bound to the image subresource range, so applications must: ensure that all
memory writes have been made
<<synchronization-dependencies-available-and-visible, available>> before a
layout transition is executed.
Available memory is automatically made visible to a layout transition, and
writes performed by a layout transition are automatically made available.

Layout transitions always apply to a particular image subresource range, and
specify both an old layout and new layout.
The old layout must: either be ename:VK_IMAGE_LAYOUT_UNDEFINED, or match the
current layout of the image subresource range.
If the old layout matches the current layout of the image subresource range,
the transition preserves the contents of that range.
If the old layout is ename:VK_IMAGE_LAYOUT_UNDEFINED, the contents of that
range may: be discarded.

ifdef::VK_VERSION_1_1,VK_KHR_device_group[]
As image layout transitions may: perform read and write accesses on the
memory bound to the image, if the image subresource affected by the layout
transition is bound to peer memory for any device in the current device mask
then the memory heap the bound memory comes from must: support the
ename:VK_PEER_MEMORY_FEATURE_GENERIC_SRC_BIT and
ename:VK_PEER_MEMORY_FEATURE_GENERIC_DST_BIT capabilities as returned by
flink:vkGetDeviceGroupPeerMemoryFeatures.
endif::VK_VERSION_1_1,VK_KHR_device_group[]

[NOTE]
.Note
====
Applications must: ensure that layout transitions happen-after all
operations accessing the image with the old layout, and happen-before any
operations that will access the image with the new layout.
Layout transitions are potentially read/write operations, so not defining
appropriate memory dependencies to guarantee this will result in a data
race.
====

Image layout transitions interact with <<resources-memory-aliasing,memory
aliasing>>.


[[synchronization-image-barrier-layout-transition-order]]
Layout transitions that are performed via image memory barriers execute in
their entirety in <<synchronization-submission-order, submission order>>,
relative to other image layout transitions submitted to the same queue,
including those performed by <<renderpass, render passes>>.
In effect there is an implicit execution dependency from each such layout
transition to all layout transitions previously submitted to the same queue.

ifdef::VK_EXT_sample_locations[]

The image layout of each image subresource of a depth/stencil image created
with ename:VK_IMAGE_CREATE_SAMPLE_LOCATIONS_COMPATIBLE_DEPTH_BIT_EXT is
dependent on the last sample locations used to render to the image
subresource as a depth/stencil attachment, thus when the pname:image member
of an <<synchronization-image-memory-barriers, image memory barrier>> is an
image created with this flag the application can: chain a
slink:VkSampleLocationsInfoEXT structure to the pname:pNext chain of
ifdef::VK_KHR_synchronization2[]
slink:VkImageMemoryBarrier2KHR or
endif::VK_KHR_synchronization2[]
slink:VkImageMemoryBarrier to specify the sample locations to use during any
image layout transition.

If the sname:VkSampleLocationsInfoEXT structure does not match the sample
location state last used to render to the image subresource range specified
by pname:subresourceRange, or if no sname:VkSampleLocationsInfoEXT structure
is present, then the contents of the given image subresource range becomes
undefined: as if pname:oldLayout would equal
ename:VK_IMAGE_LAYOUT_UNDEFINED.

endif::VK_EXT_sample_locations[]


[[synchronization-pipeline-stages]]
=== Pipeline Stages

The work performed by an <<fundamentals-queueoperation-command-types, action
or synchronization command>> consists of multiple operations, which are
performed as a sequence of logically independent steps known as _pipeline
stages_.
The exact pipeline stages executed depend on the particular command that is
used, and current command buffer state when the command was recorded.
<<drawing,Drawing commands>>, <<dispatch,dispatching commands>>,
<<copies,copy commands>>, <<clears,clear commands>>, and <<synchronization,
synchronization commands>> all execute in different sets of
<<VkPipelineStageFlagBits,pipeline stages>>.
<<synchronization, Synchronization commands>> do not execute in a defined
pipeline stage.

[NOTE]
.Note
====
Operations performed by synchronization commands (e.g.
<<synchronization-dependencies-available-and-visible, availability and
visibility operations>>) are not executed by a defined pipeline stage.
However other commands can still synchronize with them by using the
<<synchronization-dependencies-scopes, synchronization scopes>> to create a
<<synchronization-dependencies-chains, dependency chain>>.
====

Execution of operations across pipeline stages must: adhere to
<<synchronization-implicit, implicit ordering guarantees>>, particularly
including <<synchronization-pipeline-stages-order, pipeline stage order>>.
Otherwise, execution across pipeline stages may: overlap or execute out of
order with regards to other stages, unless otherwise enforced by an
execution dependency.

Several of the synchronization commands include pipeline stage parameters,
restricting the <<synchronization-dependencies-scopes, synchronization
scopes>> for that command to just those stages.
This allows fine grained control over the exact execution dependencies and
accesses performed by action commands.
Implementations should: use these pipeline stages to avoid unnecessary
stalls or cache flushing.

ifdef::VK_KHR_synchronization2[]
[open,refpage='VkPipelineStageFlagBits2KHR',desc='Pipeline stage flags for VkPipelineStageFlags2KHR',type='enums']
--
Bits which can: be set in a tlink:VkPipelineStageFlags2KHR mask, specifying
stages of execution, are:

ifdef::editing-notes[]
[NOTE]
.editing-note
====
The many places pipeline stage flags are used are not currently listed here.
====
endif::editing-notes[]

include::{generated}/api/enums/VkPipelineStageFlagBits2KHR.txt[]

  * ename:VK_PIPELINE_STAGE_2_NONE_KHR specifies no stages of execution.
  * ename:VK_PIPELINE_STAGE_2_DRAW_INDIRECT_BIT_KHR specifies the stage of
    the pipeline where indirect command parameters are consumed.
ifdef::VK_NV_device_generated_commands[]
    This stage also includes reading commands written by
    flink:vkCmdPreprocessGeneratedCommandsNV.
endif::VK_NV_device_generated_commands[]
ifdef::VK_NV_mesh_shader[]
  * ename:VK_PIPELINE_STAGE_2_TASK_SHADER_BIT_NV specifies the task shader
    stage.
  * ename:VK_PIPELINE_STAGE_2_MESH_SHADER_BIT_NV specifies the mesh shader
    stage.
endif::VK_NV_mesh_shader[]
  * ename:VK_PIPELINE_STAGE_2_INDEX_INPUT_BIT_KHR specifies the stage of the
    pipeline where index buffers are consumed.
  * ename:VK_PIPELINE_STAGE_2_VERTEX_ATTRIBUTE_INPUT_BIT_KHR specifies the
    stage of the pipeline where vertex buffers are consumed.
  * ename:VK_PIPELINE_STAGE_2_VERTEX_INPUT_BIT_KHR is equivalent to the
    logical OR of:
  ** ename:VK_PIPELINE_STAGE_2_INDEX_INPUT_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_VERTEX_ATTRIBUTE_INPUT_BIT_KHR
  * ename:VK_PIPELINE_STAGE_2_VERTEX_SHADER_BIT_KHR specifies the vertex
    shader stage.
  * ename:VK_PIPELINE_STAGE_2_TESSELLATION_CONTROL_SHADER_BIT_KHR specifies
    the tessellation control shader stage.
  * ename:VK_PIPELINE_STAGE_2_TESSELLATION_EVALUATION_SHADER_BIT_KHR
    specifies the tessellation evaluation shader stage.
  * ename:VK_PIPELINE_STAGE_2_GEOMETRY_SHADER_BIT_KHR specifies the geometry
    shader stage.
  * ename:VK_PIPELINE_STAGE_2_PRE_RASTERIZATION_SHADERS_BIT_KHR is
    equivalent to specifying all supported
    <<pipeline-graphics-subsets-pre-rasterization,pre-rasterization shader
    stages>>:
  ** ename:VK_PIPELINE_STAGE_2_VERTEX_SHADER_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_TESSELLATION_CONTROL_SHADER_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_TESSELLATION_EVALUATION_SHADER_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_GEOMETRY_SHADER_BIT_KHR
ifdef::VK_NV_mesh_shader[]
  ** ename:VK_PIPELINE_STAGE_2_TASK_SHADER_BIT_NV
  ** ename:VK_PIPELINE_STAGE_2_MESH_SHADER_BIT_NV
endif::VK_NV_mesh_shader[]
  * ename:VK_PIPELINE_STAGE_2_FRAGMENT_SHADER_BIT_KHR specifies the fragment
    shader stage.
  * ename:VK_PIPELINE_STAGE_2_EARLY_FRAGMENT_TESTS_BIT_KHR specifies the
    stage of the pipeline where early fragment tests (depth and stencil
    tests before fragment shading) are performed.
    This stage also includes <<renderpass-load-store-ops, subpass load
    operations>> for framebuffer attachments with a depth/stencil format.
  * ename:VK_PIPELINE_STAGE_2_LATE_FRAGMENT_TESTS_BIT_KHR specifies the
    stage of the pipeline where late fragment tests (depth and stencil tests
    after fragment shading) are performed.
    This stage also includes <<renderpass-load-store-ops, subpass store
    operations>> for framebuffer attachments with a depth/stencil format.
  * ename:VK_PIPELINE_STAGE_2_COLOR_ATTACHMENT_OUTPUT_BIT_KHR specifies the
    stage of the pipeline after blending where the final color values are
    output from the pipeline.
    This stage also includes <<renderpass-load-store-ops, subpass load and
    store operations>> and multisample resolve operations for framebuffer
    attachments with a color
ifdef::VK_VERSION_1_2,VK_KHR_depth_stencil_resolve[]
    or depth/stencil
endif::VK_VERSION_1_2,VK_KHR_depth_stencil_resolve[]
    format.
  * ename:VK_PIPELINE_STAGE_2_COMPUTE_SHADER_BIT_KHR specifies the compute
    shader stage.
  * ename:VK_PIPELINE_STAGE_2_HOST_BIT_KHR specifies a pseudo-stage
    indicating execution on the host of reads/writes of device memory.
    This stage is not invoked by any commands recorded in a command buffer.
  * ename:VK_PIPELINE_STAGE_2_COPY_BIT_KHR specifies the execution of all
    <<copies,copy commands>>, including flink:vkCmdCopyQueryPoolResults.
  * ename:VK_PIPELINE_STAGE_2_BLIT_BIT_KHR specifies the execution of
    flink:vkCmdBlitImage.
  * ename:VK_PIPELINE_STAGE_2_RESOLVE_BIT_KHR specifies the execution of
    flink:vkCmdResolveImage.
  * ename:VK_PIPELINE_STAGE_2_CLEAR_BIT_KHR specifies the execution of
    <<clears,clear commands>>, with the exception of
    flink:vkCmdClearAttachments.
  * ename:VK_PIPELINE_STAGE_2_ALL_TRANSFER_BIT_KHR is equivalent to
    specifying all of:
  ** ename:VK_PIPELINE_STAGE_2_COPY_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_BLIT_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_RESOLVE_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_CLEAR_BIT_KHR
ifdef::VK_KHR_ray_tracing_pipeline,VK_NV_ray_tracing[]
  * ename:VK_PIPELINE_STAGE_2_RAY_TRACING_SHADER_BIT_KHR specifies the
    execution of the ray tracing shader stages.
endif::VK_KHR_ray_tracing_pipeline,VK_NV_ray_tracing[]
ifdef::VK_KHR_acceleration_structure,VK_NV_ray_tracing[]
  * ename:VK_PIPELINE_STAGE_2_ACCELERATION_STRUCTURE_BUILD_BIT_KHR specifies
    the execution of <<acceleration-structure, acceleration structure
    commands>>.
endif::VK_KHR_acceleration_structure,VK_NV_ray_tracing[]
  * ename:VK_PIPELINE_STAGE_2_ALL_GRAPHICS_BIT_KHR specifies the execution
    of all graphics pipeline stages, and is equivalent to the logical OR of:
  ** ename:VK_PIPELINE_STAGE_2_DRAW_INDIRECT_BIT_KHR
ifdef::VK_NV_mesh_shader[]
  ** ename:VK_PIPELINE_STAGE_2_TASK_SHADER_BIT_NV
  ** ename:VK_PIPELINE_STAGE_2_MESH_SHADER_BIT_NV
endif::VK_NV_mesh_shader[]
  ** ename:VK_PIPELINE_STAGE_2_VERTEX_INPUT_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_VERTEX_SHADER_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_TESSELLATION_CONTROL_SHADER_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_TESSELLATION_EVALUATION_SHADER_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_GEOMETRY_SHADER_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_FRAGMENT_SHADER_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_EARLY_FRAGMENT_TESTS_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_LATE_FRAGMENT_TESTS_BIT_KHR
  ** ename:VK_PIPELINE_STAGE_2_COLOR_ATTACHMENT_OUTPUT_BIT_KHR
ifdef::VK_EXT_conditional_rendering[]
  ** ename:VK_PIPELINE_STAGE_2_CONDITIONAL_RENDERING_BIT_EXT
endif::VK_EXT_conditional_rendering[]
ifdef::VK_EXT_transform_feedback[]
  ** ename:VK_PIPELINE_STAGE_2_TRANSFORM_FEEDBACK_BIT_EXT
endif::VK_EXT_transform_feedback[]
ifdef::VK_NV_shading_rate_image[]
  ** ename:VK_PIPELINE_STAGE_2_SHADING_RATE_IMAGE_BIT_NV
endif::VK_NV_shading_rate_image[]
ifdef::VK_EXT_fragment_density_map[]
  ** ename:VK_PIPELINE_STAGE_2_FRAGMENT_DENSITY_PROCESS_BIT_EXT
endif::VK_EXT_fragment_density_map[]
ifdef::VK_HUAWEI_invocation_mask[]
  ** ename:VK_PIPELINE_STAGE_2_INVOCATION_MASK_BIT_HUAWEI
endif::VK_HUAWEI_invocation_mask[]
  * ename:VK_PIPELINE_STAGE_2_ALL_COMMANDS_BIT_KHR specifies all operations
    performed by all commands supported on the queue it is used with.
ifdef::VK_EXT_conditional_rendering[]
  * ename:VK_PIPELINE_STAGE_2_CONDITIONAL_RENDERING_BIT_EXT specifies the
    stage of the pipeline where the predicate of conditional rendering is
    consumed.
endif::VK_EXT_conditional_rendering[]
ifdef::VK_EXT_transform_feedback[]
  * ename:VK_PIPELINE_STAGE_2_TRANSFORM_FEEDBACK_BIT_EXT specifies the stage
    of the pipeline where vertex attribute output values are written to the
    transform feedback buffers.
endif::VK_EXT_transform_feedback[]
ifdef::VK_NV_device_generated_commands[]
  * ename:VK_PIPELINE_STAGE_2_COMMAND_PREPROCESS_BIT_NV specifies the stage
    of the pipeline where device-side generation of commands via
    flink:vkCmdPreprocessGeneratedCommandsNV is handled.
endif::VK_NV_device_generated_commands[]
ifdef::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
  * ename:VK_PIPELINE_STAGE_2_FRAGMENT_SHADING_RATE_ATTACHMENT_BIT_KHR
    specifies the stage of the pipeline where the
ifdef::VK_KHR_fragment_shading_rate[]
    <<primsrast-fragment-shading-rate-attachment, fragment shading rate
    attachment>>
endif::VK_KHR_fragment_shading_rate[]
ifdef::VK_KHR_fragment_shading_rate+VK_NV_shading_rate_image[or]
ifdef::VK_NV_shading_rate_image[]
    <<primsrast-shading-rate-image, shading rate image>>
endif::VK_NV_shading_rate_image[]
    is read to determine the fragment shading rate for portions of a
    rasterized primitive.
endif::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
ifdef::VK_EXT_fragment_density_map[]
  * ename:VK_PIPELINE_STAGE_2_FRAGMENT_DENSITY_PROCESS_BIT_EXT specifies the
    stage of the pipeline where the fragment density map is read to
    <<fragmentdensitymapops,generate the fragment areas>>.
endif::VK_EXT_fragment_density_map[]
ifdef::VK_HUAWEI_invocation_mask[]
  * ename:VK_PIPELINE_STAGE_2_INVOCATION_MASK_BIT_HUAWEI specifies the stage
    of the pipeline where the invocation mask image is read by the
    implementation to optimize the ray dispatch.
endif::VK_HUAWEI_invocation_mask[]
ifdef::VK_KHR_video_decode_queue[]
  * ename:VK_PIPELINE_STAGE_2_VIDEO_DECODE_BIT_KHR specifies the stage of
    the pipeline where <<video-decode-operations, video decode operation>>
    are performed.
endif::VK_KHR_video_decode_queue[]
ifdef::VK_KHR_video_encode_queue[]
  * ename:VK_PIPELINE_STAGE_2_VIDEO_ENCODE_BIT_KHR specifies the stage of
    the pipeline where <<video-encode-operations, video encode operation>>
    are performed.
endif::VK_KHR_video_encode_queue[]
ifdef::VK_HUAWEI_subpass_shading[]
  * ename:VK_PIPELINE_STAGE_2_SUBPASS_SHADING_BIT_HUAWEI specifies the
    subpass shading shader stage.
endif::VK_HUAWEI_subpass_shading[]
  * ename:VK_PIPELINE_STAGE_2_TOP_OF_PIPE_BIT_KHR is equivalent to
    ename:VK_PIPELINE_STAGE_2_ALL_COMMANDS_BIT_KHR with
    tlink:VkAccessFlags2KHR set to `0` when specified in the second
    synchronization scope, but equivalent to
    ename:VK_PIPELINE_STAGE_2_NONE_KHR in the first scope.
  * ename:VK_PIPELINE_STAGE_2_BOTTOM_OF_PIPE_BIT_KHR is equivalent to
    ename:VK_PIPELINE_STAGE_2_ALL_COMMANDS_BIT_KHR with
    tlink:VkAccessFlags2KHR set to `0` when specified in the first
    synchronization scope, but equivalent to
    ename:VK_PIPELINE_STAGE_2_NONE_KHR in the second scope.

[NOTE]
.Note
====
The etext:TOP and etext:BOTTOM pipeline stages are deprecated, and
applications should prefer ename:VK_PIPELINE_STAGE_2_ALL_COMMANDS_BIT_KHR
and ename:VK_PIPELINE_STAGE_2_NONE_KHR.
====

[NOTE]
.Note
====
The tname:VkPipelineStageFlags2KHR bitmask goes beyond the 31 individual bit
flags allowable within a C99 enum, which is how
elink:VkPipelineStageFlagBits is defined.
The first 31 values are common to both, and are interchangeable.
====
--

[open,refpage='VkPipelineStageFlags2KHR',desc='64-bit mask of pipeline stage flags',type='flags']
--
tname:VkPipelineStageFlags2KHR is a bitmask type for setting a mask of zero
or more elink:VkPipelineStageFlagBits2KHR flags:

include::{generated}/api/flags/VkPipelineStageFlags2KHR.txt[]
--
endif::VK_KHR_synchronization2[]

[open,refpage='VkPipelineStageFlagBits',desc='Bitmask specifying pipeline stages',type='enums']
--
Bits which can: be set in a tlink:VkPipelineStageFlags mask, specifying
stages of execution, are:

include::{generated}/api/enums/VkPipelineStageFlagBits.txt[]

ifdef::VK_KHR_synchronization2[]
These values all have the same meaning as the equivalently named values for
tlink:VkPipelineStageFlags2KHR.
endif::VK_KHR_synchronization2[]

ifdef::VK_KHR_synchronization2[]
  * ename:VK_PIPELINE_STAGE_NONE_KHR specifies no stages of execution.
endif::VK_KHR_synchronization2[]
  * ename:VK_PIPELINE_STAGE_DRAW_INDIRECT_BIT specifies the stage of the
    pipeline where stext:VkDrawIndirect* / stext:VkDispatchIndirect* /
    stext:VkTraceRaysIndirect* data structures are consumed.
ifdef::VK_NV_device_generated_commands[]
    This stage also includes reading commands written by
    flink:vkCmdExecuteGeneratedCommandsNV.
endif::VK_NV_device_generated_commands[]
ifdef::VK_NV_mesh_shader[]
  * ename:VK_PIPELINE_STAGE_TASK_SHADER_BIT_NV specifies the task shader
    stage.
  * ename:VK_PIPELINE_STAGE_MESH_SHADER_BIT_NV specifies the mesh shader
    stage.
endif::VK_NV_mesh_shader[]
  * ename:VK_PIPELINE_STAGE_VERTEX_INPUT_BIT specifies the stage of the
    pipeline where vertex and index buffers are consumed.
  * ename:VK_PIPELINE_STAGE_VERTEX_SHADER_BIT specifies the vertex shader
    stage.
  * ename:VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT specifies the
    tessellation control shader stage.
  * ename:VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT specifies the
    tessellation evaluation shader stage.
  * ename:VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT specifies the geometry
    shader stage.
  * ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT specifies the fragment
    shader stage.
  * ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT specifies the stage of
    the pipeline where early fragment tests (depth and stencil tests before
    fragment shading) are performed.
    This stage also includes <<renderpass-load-store-ops, subpass load
    operations>> for framebuffer attachments with a depth/stencil format.
  * ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT specifies the stage of
    the pipeline where late fragment tests (depth and stencil tests after
    fragment shading) are performed.
    This stage also includes <<renderpass-load-store-ops, subpass store
    operations>> for framebuffer attachments with a depth/stencil format.
  * ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT specifies the stage
    of the pipeline after blending where the final color values are output
    from the pipeline.
    This stage also includes <<renderpass-load-store-ops, subpass load and
    store operations>> and multisample resolve operations for framebuffer
    attachments with a color
ifdef::VK_VERSION_1_2,VK_KHR_depth_stencil_resolve[]
    or depth/stencil
endif::VK_VERSION_1_2,VK_KHR_depth_stencil_resolve[]
    format.
  * ename:VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT specifies the execution of a
    compute shader.
  * [[synchronization-pipeline-stages-transfer]]
    ename:VK_PIPELINE_STAGE_TRANSFER_BIT specifies the following commands:
  ** All <<copies,copy commands>>, including flink:vkCmdCopyQueryPoolResults
ifndef::VK_KHR_copy_commands2[]
  ** flink:vkCmdBlitImage
  ** flink:vkCmdResolveImage
endif::VK_KHR_copy_commands2[]
ifdef::VK_KHR_copy_commands2[]
  ** flink:vkCmdBlitImage2KHR and flink:vkCmdBlitImage
  ** flink:vkCmdResolveImage2KHR and flink:vkCmdResolveImage
endif::VK_KHR_copy_commands2[]
  ** All <<clears,clear commands>>, with the exception of
     flink:vkCmdClearAttachments
  * ename:VK_PIPELINE_STAGE_HOST_BIT specifies a pseudo-stage indicating
    execution on the host of reads/writes of device memory.
    This stage is not invoked by any commands recorded in a command buffer.
ifdef::VK_NV_ray_tracing,VK_KHR_acceleration_structure[]
  * ename:VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR specifies
    the execution of
ifdef::VK_NV_ray_tracing[]
    flink:vkCmdBuildAccelerationStructureNV,
    flink:vkCmdCopyAccelerationStructureNV,
    flink:vkCmdWriteAccelerationStructuresPropertiesNV
endif::VK_NV_ray_tracing[]
ifdef::VK_NV_ray_tracing+VK_KHR_acceleration_structure[,]
ifdef::VK_KHR_acceleration_structure[]
    flink:vkCmdBuildAccelerationStructuresKHR,
    flink:vkCmdBuildAccelerationStructuresIndirectKHR,
    flink:vkCmdCopyAccelerationStructureKHR,
    flink:vkCmdCopyAccelerationStructureToMemoryKHR,
    flink:vkCmdCopyMemoryToAccelerationStructureKHR, and
    flink:vkCmdWriteAccelerationStructuresPropertiesKHR.
endif::VK_KHR_acceleration_structure[]
endif::VK_NV_ray_tracing,VK_KHR_acceleration_structure[]
ifdef::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
  * ename:VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR specifies the
    execution of the ray tracing shader stages, via
ifdef::VK_NV_ray_tracing[flink:vkCmdTraceRaysNV]
ifdef::VK_NV_ray_tracing+VK_KHR_ray_tracing_pipeline[,]
ifdef::VK_KHR_ray_tracing_pipeline[flink:vkCmdTraceRaysKHR, or flink:vkCmdTraceRaysIndirectKHR]
endif::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
  * ename:VK_PIPELINE_STAGE_ALL_GRAPHICS_BIT specifies the execution of all
    graphics pipeline stages, and is equivalent to the logical OR of:
  ** ename:VK_PIPELINE_STAGE_DRAW_INDIRECT_BIT
ifdef::VK_NV_mesh_shader[]
  ** ename:VK_PIPELINE_STAGE_TASK_SHADER_BIT_NV
  ** ename:VK_PIPELINE_STAGE_MESH_SHADER_BIT_NV
endif::VK_NV_mesh_shader[]
  ** ename:VK_PIPELINE_STAGE_VERTEX_INPUT_BIT
  ** ename:VK_PIPELINE_STAGE_VERTEX_SHADER_BIT
  ** ename:VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT
  ** ename:VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT
  ** ename:VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT
  ** ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT
  ** ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT
  ** ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT
  ** ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT
ifdef::VK_EXT_conditional_rendering[]
  ** ename:VK_PIPELINE_STAGE_CONDITIONAL_RENDERING_BIT_EXT
endif::VK_EXT_conditional_rendering[]
ifdef::VK_EXT_transform_feedback[]
  ** ename:VK_PIPELINE_STAGE_TRANSFORM_FEEDBACK_BIT_EXT
endif::VK_EXT_transform_feedback[]
ifdef::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
  ** ename:VK_PIPELINE_STAGE_FRAGMENT_SHADING_RATE_ATTACHMENT_BIT_KHR
endif::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
ifdef::VK_EXT_fragment_density_map[]
  ** ename:VK_PIPELINE_STAGE_FRAGMENT_DENSITY_PROCESS_BIT_EXT
endif::VK_EXT_fragment_density_map[]
  * ename:VK_PIPELINE_STAGE_ALL_COMMANDS_BIT specifies all operations
    performed by all commands supported on the queue it is used with.
ifdef::VK_EXT_conditional_rendering[]
  * ename:VK_PIPELINE_STAGE_CONDITIONAL_RENDERING_BIT_EXT specifies the
    stage of the pipeline where the predicate of conditional rendering is
    consumed.
endif::VK_EXT_conditional_rendering[]
ifdef::VK_EXT_transform_feedback[]
  * ename:VK_PIPELINE_STAGE_TRANSFORM_FEEDBACK_BIT_EXT specifies the stage
    of the pipeline where vertex attribute output values are written to the
    transform feedback buffers.
endif::VK_EXT_transform_feedback[]
ifdef::VK_NV_device_generated_commands[]
  * ename:VK_PIPELINE_STAGE_COMMAND_PREPROCESS_BIT_NV specifies the stage of
    the pipeline where device-side preprocessing for generated commands via
    flink:vkCmdPreprocessGeneratedCommandsNV is handled.
endif::VK_NV_device_generated_commands[]
ifdef::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
  * ename:VK_PIPELINE_STAGE_FRAGMENT_SHADING_RATE_ATTACHMENT_BIT_KHR
    specifies the stage of the pipeline where the
ifdef::VK_KHR_fragment_shading_rate[]
    <<primsrast-fragment-shading-rate-attachment, fragment shading rate
    attachment>>
endif::VK_KHR_fragment_shading_rate[]
ifdef::VK_KHR_fragment_shading_rate+VK_NV_shading_rate_image[or]
ifdef::VK_NV_shading_rate_image[]
    <<primsrast-shading-rate-image, shading rate image>>
endif::VK_NV_shading_rate_image[]
    is read to determine the fragment shading rate for portions of a
    rasterized primitive.
endif::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
ifdef::VK_EXT_fragment_density_map[]
  * ename:VK_PIPELINE_STAGE_FRAGMENT_DENSITY_PROCESS_BIT_EXT specifies the
    stage of the pipeline where the fragment density map is read to
    <<fragmentdensitymapops,generate the fragment areas>>.
endif::VK_EXT_fragment_density_map[]
  * ename:VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT is equivalent to
    ename:VK_PIPELINE_STAGE_ALL_COMMANDS_BIT with tlink:VkAccessFlags set to
    `0` when specified in the second synchronization scope, but specifies no
    stage of execution when specified in the first scope.
  * ename:VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT is equivalent to
    ename:VK_PIPELINE_STAGE_ALL_COMMANDS_BIT with tlink:VkAccessFlags set to
    `0` when specified in the first synchronization scope, but specifies no
    stage of execution when specified in the second scope.
--

[open,refpage='VkPipelineStageFlags',desc='Bitmask of VkPipelineStageFlagBits',type='flags']
--
include::{generated}/api/flags/VkPipelineStageFlags.txt[]

tname:VkPipelineStageFlags is a bitmask type for setting a mask of zero or
more elink:VkPipelineStageFlagBits.
--

[[synchronization-pipeline-stages-masks]]
If a synchronization command includes a source stage mask, its first
<<synchronization-dependencies-scopes, synchronization scope>> only includes
execution of the pipeline stages specified in that mask, and its first
<<synchronization-dependencies-access-scopes, access scope>> only includes
memory accesses performed by pipeline stages specified in that mask.

If a synchronization command includes a destination stage mask, its second
<<synchronization-dependencies-scopes, synchronization scope>> only includes
execution of the pipeline stages specified in that mask, and its second
<<synchronization-dependencies-access-scopes, access scope>> only includes
memory access performed by pipeline stages specified in that mask.

[NOTE]
.Note
====
Including a particular pipeline stage in the first
<<synchronization-dependencies-scopes, synchronization scope>> of a command
implicitly includes <<synchronization-pipeline-stages-order, logically
earlier>> pipeline stages in the synchronization scope.
Similarly, the second <<synchronization-dependencies-scopes, synchronization
scope>> includes <<synchronization-pipeline-stages-order, logically later>>
pipeline stages.

However, note that <<synchronization-dependencies-access-scopes, access
scopes>> are not affected in this way - only the precise stages specified
are considered part of each access scope.
====

Certain pipeline stages are only available on queues that support a
particular set of operations.
The following table lists, for each pipeline stage flag, which queue
capability flag must: be supported by the queue.
When multiple flags are enumerated in the second column of the table, it
means that the pipeline stage is supported on the queue if it supports any
of the listed capability flags.
For further details on queue capabilities see
<<devsandqueues-physical-device-enumeration,Physical Device Enumeration>>
and <<devsandqueues-queues,Queues>>.

[[synchronization-pipeline-stages-supported]]
.Supported pipeline stage flags
[cols="60%,40%",options="header"]
|====
|Pipeline stage flag                                          | Required queue capability flag
|ename:VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT                      | None required
|ename:VK_PIPELINE_STAGE_DRAW_INDIRECT_BIT                    | ename:VK_QUEUE_GRAPHICS_BIT or ename:VK_QUEUE_COMPUTE_BIT
|ename:VK_PIPELINE_STAGE_VERTEX_INPUT_BIT                     | ename:VK_QUEUE_GRAPHICS_BIT
|ename:VK_PIPELINE_STAGE_VERTEX_SHADER_BIT                    | ename:VK_QUEUE_GRAPHICS_BIT
|ename:VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT      | ename:VK_QUEUE_GRAPHICS_BIT
|ename:VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT   | ename:VK_QUEUE_GRAPHICS_BIT
|ename:VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT                  | ename:VK_QUEUE_GRAPHICS_BIT
|ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT                  | ename:VK_QUEUE_GRAPHICS_BIT
|ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT             | ename:VK_QUEUE_GRAPHICS_BIT
|ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT              | ename:VK_QUEUE_GRAPHICS_BIT
|ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT          | ename:VK_QUEUE_GRAPHICS_BIT
|ename:VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT                   | ename:VK_QUEUE_COMPUTE_BIT
|ename:VK_PIPELINE_STAGE_TRANSFER_BIT                         | ename:VK_QUEUE_GRAPHICS_BIT, ename:VK_QUEUE_COMPUTE_BIT or ename:VK_QUEUE_TRANSFER_BIT
|ename:VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT                   | None required
|ename:VK_PIPELINE_STAGE_HOST_BIT                             | None required
|ename:VK_PIPELINE_STAGE_ALL_GRAPHICS_BIT                     | ename:VK_QUEUE_GRAPHICS_BIT
|ename:VK_PIPELINE_STAGE_ALL_COMMANDS_BIT                     | None required
ifdef::VK_EXT_conditional_rendering[]
|ename:VK_PIPELINE_STAGE_CONDITIONAL_RENDERING_BIT_EXT        | ename:VK_QUEUE_GRAPHICS_BIT or ename:VK_QUEUE_COMPUTE_BIT
endif::VK_EXT_conditional_rendering[]
ifdef::VK_EXT_transform_feedback[]
|ename:VK_PIPELINE_STAGE_TRANSFORM_FEEDBACK_BIT_EXT           | ename:VK_QUEUE_GRAPHICS_BIT
endif::VK_EXT_transform_feedback[]
ifdef::VK_NV_device_generated_commands[]
|ename:VK_PIPELINE_STAGE_COMMAND_PREPROCESS_BIT_NV            | ename:VK_QUEUE_GRAPHICS_BIT or ename:VK_QUEUE_COMPUTE_BIT
endif::VK_NV_device_generated_commands[]
ifdef::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
|ename:VK_PIPELINE_STAGE_FRAGMENT_SHADING_RATE_ATTACHMENT_BIT_KHR | ename:VK_QUEUE_GRAPHICS_BIT
endif::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
ifdef::VK_NV_mesh_shader[]
|ename:VK_PIPELINE_STAGE_TASK_SHADER_BIT_NV                   | ename:VK_QUEUE_GRAPHICS_BIT
|ename:VK_PIPELINE_STAGE_MESH_SHADER_BIT_NV                   | ename:VK_QUEUE_GRAPHICS_BIT
endif::VK_NV_mesh_shader[]
ifdef::VK_NV_ray_tracing,VK_KHR_acceleration_structure[]
|ename:VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR | ename:VK_QUEUE_COMPUTE_BIT
endif::VK_NV_ray_tracing,VK_KHR_acceleration_structure[]
ifdef::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
|ename:VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR           | ename:VK_QUEUE_COMPUTE_BIT
endif::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
ifdef::VK_EXT_fragment_density_map[]
|ename:VK_PIPELINE_STAGE_FRAGMENT_DENSITY_PROCESS_BIT_EXT     | ename:VK_QUEUE_GRAPHICS_BIT
endif::VK_EXT_fragment_density_map[]
ifdef::VK_HUAWEI_subpass_shading[]
|ename:VK_PIPELINE_STAGE_2_SUBPASS_SHADING_BIT_HUAWEI         | ename:VK_QUEUE_GRAPHICS_BIT
endif::VK_HUAWEI_subpass_shading[]
|====

[[synchronization-pipeline-stages-order]]
Pipeline stages that execute as a result of a command logically complete
execution in a specific order, such that completion of a logically later
pipeline stage must: not happen-before completion of a logically earlier
stage.
This means that including any stage in the source stage mask for a
particular synchronization command also implies that any logically earlier
stages are included in *A~S~* for that command.

Similarly, initiation of a logically earlier pipeline stage must: not
happen-after initiation of a logically later pipeline stage.
Including any given stage in the destination stage mask for a particular
synchronization command also implies that any logically later stages are
included in *B~S~* for that command.

[NOTE]
.Note
====
Implementations may: not support synchronization at every pipeline stage for
every synchronization operation.
If a pipeline stage that an implementation does not support synchronization
for appears in a source stage mask, it may: substitute any logically later
stage in its place for the first synchronization scope.
If a pipeline stage that an implementation does not support synchronization
for appears in a destination stage mask, it may: substitute any logically
earlier stage in its place for the second synchronization scope.

For example, if an implementation is unable to signal an event immediately
after vertex shader execution is complete, it may: instead signal the event
after color attachment output has completed.

If an implementation makes such a substitution, it must: not affect the
semantics of execution or memory dependencies or image and buffer memory
barriers.
====

[[synchronization-pipeline-stages-types]][[synchronization-pipeline-graphics]]
<<pipelines-graphics, Graphics pipelines>> are executable on queues
supporting ename:VK_QUEUE_GRAPHICS_BIT.
Stages executed by graphics pipelines can: only be specified in commands
recorded for queues supporting ename:VK_QUEUE_GRAPHICS_BIT.

The graphics
ifdef::VK_NV_mesh_shader[]
primitive
endif::VK_NV_mesh_shader[]
pipeline executes the following stages, with the logical ordering of the
stages matching the order specified here:

  * ename:VK_PIPELINE_STAGE_DRAW_INDIRECT_BIT
ifdef::VK_KHR_synchronization2[]
  * ename:VK_PIPELINE_STAGE_2_INDEX_INPUT_BIT_KHR
  * ename:VK_PIPELINE_STAGE_2_VERTEX_ATTRIBUTE_INPUT_BIT_KHR
endif::VK_KHR_synchronization2[]
ifndef::VK_KHR_synchronization2[]
  * ename:VK_PIPELINE_STAGE_VERTEX_INPUT_BIT
endif::VK_KHR_synchronization2[]
  * ename:VK_PIPELINE_STAGE_VERTEX_SHADER_BIT
  * ename:VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT
  * ename:VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT
  * ename:VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT
ifdef::VK_EXT_transform_feedback[]
  * ename:VK_PIPELINE_STAGE_TRANSFORM_FEEDBACK_BIT_EXT
endif::VK_EXT_transform_feedback[]
ifdef::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
  * ename:VK_PIPELINE_STAGE_FRAGMENT_SHADING_RATE_ATTACHMENT_BIT_KHR
endif::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
  * ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT
  * ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT
  * ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT
  * ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT

ifdef::VK_NV_mesh_shader[]
The graphics mesh pipeline executes the following stages, with the logical
ordering of the stages matching the order specified here:

  * ename:VK_PIPELINE_STAGE_DRAW_INDIRECT_BIT
  * ename:VK_PIPELINE_STAGE_TASK_SHADER_BIT_NV
  * ename:VK_PIPELINE_STAGE_MESH_SHADER_BIT_NV
ifdef::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
  * ename:VK_PIPELINE_STAGE_FRAGMENT_SHADING_RATE_ATTACHMENT_BIT_KHR
endif::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
  * ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT
  * ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT
  * ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT
  * ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT
endif::VK_NV_mesh_shader[]

For the compute pipeline, the following stages occur in this order:

  * ename:VK_PIPELINE_STAGE_DRAW_INDIRECT_BIT
  * ename:VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT

ifdef::VK_HUAWEI_subpass_shading[]
For the subpass shading pipeline, the following stages occur in this order:

  * ename:VK_PIPELINE_STAGE_2_SUBPASS_SHADING_BIT_HUAWEI
endif::VK_HUAWEI_subpass_shading[]

ifdef::VK_EXT_fragment_density_map[]
For graphics pipeline commands executing in a render pass with a fragment
density map attachment, the following pipeline stage where the fragment
density map read happens has no particular order relative to the other
stages, except that it is logically earlier than
ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT:

  * ename:VK_PIPELINE_STAGE_FRAGMENT_DENSITY_PROCESS_BIT_EXT
  * ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT
endif::VK_EXT_fragment_density_map[]

ifdef::VK_EXT_conditional_rendering[]
The conditional rendering stage is formally part of both the graphics, and
the compute pipeline.
The pipeline stage where the predicate read happens has unspecified order
relative to other stages of these pipelines:

  * ename:VK_PIPELINE_STAGE_CONDITIONAL_RENDERING_BIT_EXT
endif::VK_EXT_conditional_rendering[]

For the transfer pipeline, the following stages occur in this order:

  * ename:VK_PIPELINE_STAGE_TRANSFER_BIT

For host operations, only one pipeline stage occurs, so no order is
guaranteed:

  * ename:VK_PIPELINE_STAGE_HOST_BIT

ifdef::VK_NV_device_generated_commands[]
For the command preprocessing pipeline, the following stages occur in this
order:

  * ename:VK_PIPELINE_STAGE_COMMAND_PREPROCESS_BIT_NV
endif::VK_NV_device_generated_commands[]

ifdef::VK_NV_ray_tracing,VK_KHR_acceleration_structure[]
For acceleration structure operations, only one pipeline stage occurs, so no
order is guaranteed:

  * ename:VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR

endif::VK_NV_ray_tracing,VK_KHR_acceleration_structure[]

ifdef::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
For the ray tracing pipeline, the following stages occur in this order:

  * ename:VK_PIPELINE_STAGE_DRAW_INDIRECT_BIT
  * ename:VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR

endif::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]


[[synchronization-access-types]]
=== Access Types

Memory in Vulkan can: be accessed from within shader invocations and via
some fixed-function stages of the pipeline.
The _access type_ is a function of the <<descriptorsets, descriptor type>>
used, or how a fixed-function stage accesses memory.

[[synchronization-access-masks]]
Some synchronization commands take sets of access types as parameters to
define the <<synchronization-dependencies-access-scopes, access scopes>> of
a memory dependency.
If a synchronization command includes a _source access mask_, its first
<<synchronization-dependencies-access-scopes, access scope>> only includes
accesses via the access types specified in that mask.
Similarly, if a synchronization command includes a _destination access
mask_, its second <<synchronization-dependencies-access-scopes, access
scope>> only includes accesses via the access types specified in that mask.

ifdef::VK_KHR_synchronization2[]
[open,refpage='VkAccessFlagBits2KHR',desc='Access flags for VkAccessFlags2KHR',type='enums']
--
Bits which can: be set in the pname:srcAccessMask and pname:dstAccessMask
members of slink:VkMemoryBarrier2KHR, slink:VkImageMemoryBarrier2KHR, and
slink:VkBufferMemoryBarrier2KHR, specifying access behavior, are:

include::{generated}/api/enums/VkAccessFlagBits2KHR.txt[]

  * ename:VK_ACCESS_2_NONE_KHR specifies no accesses.
  * ename:VK_ACCESS_2_MEMORY_READ_BIT_KHR specifies all read accesses.
    It is always valid in any access mask, and is treated as equivalent to
    setting all etext:READ access flags that are valid where it is used.
  * ename:VK_ACCESS_2_MEMORY_WRITE_BIT_KHR specifies all write accesses.
    It is always valid in any access mask, and is treated as equivalent to
    setting all etext:WRITE access flags that are valid where it is used.
  * ename:VK_ACCESS_2_INDIRECT_COMMAND_READ_BIT_KHR specifies read access to
    command data read from indirect buffers as part of an indirect
ifdef::VK_KHR_acceleration_structure[build,]
ifdef::VK_KHR_ray_tracing_pipeline[trace,]
    drawing or dispatch command.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_DRAW_INDIRECT_BIT_KHR pipeline stage.
  * ename:VK_ACCESS_2_INDEX_READ_BIT_KHR specifies read access to an index
    buffer as part of an indexed drawing command, bound by
    flink:vkCmdBindIndexBuffer.
    Such access occurs in the ename:VK_PIPELINE_STAGE_2_INDEX_INPUT_BIT_KHR
    pipeline stage.
  * ename:VK_ACCESS_2_VERTEX_ATTRIBUTE_READ_BIT_KHR specifies read access to
    a vertex buffer as part of a drawing command, bound by
    flink:vkCmdBindVertexBuffers.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_VERTEX_ATTRIBUTE_INPUT_BIT_KHR pipeline stage.
  * ename:VK_ACCESS_2_UNIFORM_READ_BIT_KHR specifies read access to a
    <<descriptorsets-uniformbuffer, uniform buffer>> in any shader pipeline
    stage.
  * ename:VK_ACCESS_2_INPUT_ATTACHMENT_READ_BIT_KHR specifies read access to
    an <<renderpass, input attachment>> within a render pass during
ifdef::VK_HUAWEI_subpass_shading[]
    subpass shading or
endif::VK_HUAWEI_subpass_shading[]
    fragment shading.
    Such access occurs in the
ifdef::VK_HUAWEI_subpass_shading[]
    ename:VK_PIPELINE_STAGE_2_SUBPASS_SHADING_BIT_HUAWEI or
endif::VK_HUAWEI_subpass_shading[]
    ename:VK_PIPELINE_STAGE_2_FRAGMENT_SHADER_BIT_KHR pipeline stage.
  * ename:VK_ACCESS_2_SHADER_SAMPLED_READ_BIT_KHR specifies read access to a
    <<descriptorsets-uniformtexelbuffer, uniform texel buffer>> or
    <<descriptorsets-sampledimage, sampled image>> in any shader pipeline
    stage.
  * ename:VK_ACCESS_2_SHADER_STORAGE_READ_BIT_KHR specifies read access to a
    <<descriptorsets-storagebuffer, storage buffer>>,
ifdef::VK_VERSION_1_2,VK_EXT_buffer_device_address,VK_buffer_device_address[]
    <<descriptorsets-physical-storage-buffer, physical storage buffer>>,
endif::VK_VERSION_1_2,VK_EXT_buffer_device_address,VK_buffer_device_address[]
    <<descriptorsets-storagetexelbuffer, storage texel buffer>>, or
    <<descriptorsets-storageimage, storage image>> in any shader pipeline
    stage.
  * ename:VK_ACCESS_2_SHADER_READ_BIT_KHR
ifdef::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
    specifies read access to a <<shader-binding-table, shader binding
    table>> in any shader pipeline.
    In addition, it
endif::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
    is equivalent to the logical OR of:
  ** ename:VK_ACCESS_2_UNIFORM_READ_BIT_KHR
  ** ename:VK_ACCESS_2_SHADER_SAMPLED_READ_BIT_KHR
  ** ename:VK_ACCESS_2_SHADER_STORAGE_READ_BIT_KHR
  * ename:VK_ACCESS_2_SHADER_STORAGE_WRITE_BIT_KHR specifies write access to
    a <<descriptorsets-storagebuffer, storage buffer>>,
ifdef::VK_VERSION_1_2,VK_EXT_buffer_device_address,VK_buffer_device_address[]
    <<descriptorsets-physical-storage-buffer, physical storage buffer>>,
endif::VK_VERSION_1_2,VK_EXT_buffer_device_address,VK_buffer_device_address[]
    <<descriptorsets-storagetexelbuffer, storage texel buffer>>, or
    <<descriptorsets-storageimage, storage image>> in any shader pipeline
    stage.
  * ename:VK_ACCESS_2_SHADER_WRITE_BIT_KHR is equivalent to
    ename:VK_ACCESS_2_SHADER_STORAGE_WRITE_BIT_KHR.
  * ename:VK_ACCESS_2_COLOR_ATTACHMENT_READ_BIT_KHR specifies read access to
    a <<renderpass, color attachment>>, such as via <<framebuffer-blending,
    blending>>, <<framebuffer-logicop, logic operations>>, or via certain
    <<renderpass-load-store-ops, subpass load operations>>.
ifdef::VK_EXT_blend_operation_advanced[]
    It does not include <<framebuffer-blend-advanced, advanced blend
    operations>>.
endif::VK_EXT_blend_operation_advanced[]
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_COLOR_ATTACHMENT_OUTPUT_BIT_KHR pipeline
    stage.
  * ename:VK_ACCESS_2_COLOR_ATTACHMENT_WRITE_BIT_KHR specifies write access
    to a
ifndef::VK_VERSION_1_2,VK_KHR_depth_stencil_resolve[]
    <<renderpass, color or resolve attachment>>
endif::VK_VERSION_1_2,VK_KHR_depth_stencil_resolve[]
ifdef::VK_VERSION_1_2,VK_KHR_depth_stencil_resolve[]
    <<renderpass, color, resolve, or depth/stencil resolve attachment>>
endif::VK_VERSION_1_2,VK_KHR_depth_stencil_resolve[]
    during a <<renderpass, render pass>> or via certain
    <<renderpass-load-store-ops, subpass load and store operations>>.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_COLOR_ATTACHMENT_OUTPUT_BIT_KHR pipeline
    stage.
  * ename:VK_ACCESS_2_DEPTH_STENCIL_ATTACHMENT_READ_BIT_KHR specifies read
    access to a <<renderpass, depth/stencil attachment>>, via
    <<fragops-ds-state, depth or stencil operations>> or via certain
    <<renderpass-load-store-ops, subpass load operations>>.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_EARLY_FRAGMENT_TESTS_BIT_KHR or
    ename:VK_PIPELINE_STAGE_2_LATE_FRAGMENT_TESTS_BIT_KHR pipeline stages.
  * ename:VK_ACCESS_2_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT_KHR specifies write
    access to a <<renderpass, depth/stencil attachment>>, via
    <<fragops-ds-state, depth or stencil operations>> or via certain
    <<renderpass-load-store-ops, subpass load and store operations>>.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_EARLY_FRAGMENT_TESTS_BIT_KHR or
    ename:VK_PIPELINE_STAGE_2_LATE_FRAGMENT_TESTS_BIT_KHR pipeline stages.
  * ename:VK_ACCESS_2_TRANSFER_READ_BIT_KHR specifies read access to an
    image or buffer in a <<copies, copy>> operation.
    Such access occurs in the ename:VK_PIPELINE_STAGE_2_COPY_BIT_KHR,
    ename:VK_PIPELINE_STAGE_2_BLIT_BIT_KHR, or
    ename:VK_PIPELINE_STAGE_2_RESOLVE_BIT_KHR pipeline stages.
  * ename:VK_ACCESS_2_TRANSFER_WRITE_BIT_KHR specifies write access to an
    image or buffer in a <<clears, clear>> or <<copies, copy>> operation.
    Such access occurs in the ename:VK_PIPELINE_STAGE_2_COPY_BIT_KHR,
    ename:VK_PIPELINE_STAGE_2_BLIT_BIT_KHR,
    ename:VK_PIPELINE_STAGE_2_CLEAR_BIT_KHR, or
    ename:VK_PIPELINE_STAGE_2_RESOLVE_BIT_KHR pipeline stages.
  * ename:VK_ACCESS_2_HOST_READ_BIT_KHR specifies read access by a host
    operation.
    Accesses of this type are not performed through a resource, but directly
    on memory.
    Such access occurs in the ename:VK_PIPELINE_STAGE_2_HOST_BIT_KHR
    pipeline stage.
  * ename:VK_ACCESS_2_HOST_WRITE_BIT_KHR specifies write access by a host
    operation.
    Accesses of this type are not performed through a resource, but directly
    on memory.
    Such access occurs in the ename:VK_PIPELINE_STAGE_2_HOST_BIT_KHR
    pipeline stage.
ifdef::VK_EXT_conditional_rendering[]
  * ename:VK_ACCESS_2_CONDITIONAL_RENDERING_READ_BIT_EXT specifies read
    access to a predicate as part of conditional rendering.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_CONDITIONAL_RENDERING_BIT_EXT pipeline stage.
endif::VK_EXT_conditional_rendering[]
ifdef::VK_EXT_transform_feedback[]
  * ename:VK_ACCESS_2_TRANSFORM_FEEDBACK_WRITE_BIT_EXT specifies write
    access to a transform feedback buffer made when transform feedback is
    active.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_TRANSFORM_FEEDBACK_BIT_EXT pipeline stage.
  * ename:VK_ACCESS_2_TRANSFORM_FEEDBACK_COUNTER_READ_BIT_EXT specifies read
    access to a transform feedback counter buffer which is read when
    flink:vkCmdBeginTransformFeedbackEXT executes.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_TRANSFORM_FEEDBACK_BIT_EXT pipeline stage.
  * ename:VK_ACCESS_2_TRANSFORM_FEEDBACK_COUNTER_WRITE_BIT_EXT specifies
    write access to a transform feedback counter buffer which is written
    when flink:vkCmdEndTransformFeedbackEXT executes.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_TRANSFORM_FEEDBACK_BIT_EXT pipeline stage.
endif::VK_EXT_transform_feedback[]
ifdef::VK_NV_device_generated_commands[]
  * ename:VK_ACCESS_2_COMMAND_PREPROCESS_READ_BIT_NV specifies reads from
    buffer inputs to flink:vkCmdPreprocessGeneratedCommandsNV.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_COMMAND_PREPROCESS_BIT_NV pipeline stage.
  * ename:VK_ACCESS_2_COMMAND_PREPROCESS_WRITE_BIT_NV specifies writes to
    the target command buffer preprocess outputs.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_COMMAND_PREPROCESS_BIT_NV pipeline stage.
endif::VK_NV_device_generated_commands[]
ifdef::VK_EXT_blend_operation_advanced[]
  * ename:VK_ACCESS_2_COLOR_ATTACHMENT_READ_NONCOHERENT_BIT_EXT specifies
    read access to <<renderpass, color attachments>>, including
    <<framebuffer-blend-advanced,advanced blend operations>>.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_COLOR_ATTACHMENT_OUTPUT_BIT_KHR pipeline
    stage.
endif::VK_EXT_blend_operation_advanced[]
ifdef::VK_HUAWEI_invocation_mask[]
  * ename:VK_ACCESS_2_INVOCATION_MASK_READ_BIT_HUAWEI specifies read access
    to a invocation mask image in the
    ename:VK_PIPELINE_STAGE_2_INVOCATION_MASK_BIT_HUAWEI pipeline stage.
endif::VK_HUAWEI_invocation_mask[]
ifdef::VK_KHR_acceleration_structure,VK_NV_ray_tracing[]
  * ename:VK_ACCESS_2_ACCELERATION_STRUCTURE_READ_BIT_KHR specifies read
    access to an acceleration structure as part of a trace, build, or copy
    command, or to an <<acceleration-structure-scratch, acceleration
    structure scratch buffer>> as part of a build command.
    Such access occurs in the
ifdef::VK_KHR_ray_tracing_pipeline[]
    ename:VK_PIPELINE_STAGE_2_RAY_TRACING_SHADER_BIT_KHR pipeline stage or
endif::VK_KHR_ray_tracing_pipeline[]
    ename:VK_PIPELINE_STAGE_2_ACCELERATION_STRUCTURE_BUILD_BIT_KHR pipeline
    stage.
  * ename:VK_ACCESS_2_ACCELERATION_STRUCTURE_WRITE_BIT_KHR specifies write
    access to an acceleration structure or <<acceleration-structure-scratch,
    acceleration structure scratch buffer>> as part of a build or copy
    command.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_ACCELERATION_STRUCTURE_BUILD_BIT_KHR pipeline
    stage.
endif::VK_KHR_acceleration_structure,VK_NV_ray_tracing[]
ifdef::VK_EXT_fragment_density_map[]
  * ename:VK_ACCESS_2_FRAGMENT_DENSITY_MAP_READ_BIT_EXT specifies read
    access to a <<renderpass-fragmentdensitymapattachment, fragment density
    map attachment>> during dynamic <<fragmentdensitymapops, fragment
    density map operations>>.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_FRAGMENT_DENSITY_PROCESS_BIT_EXT pipeline
    stage.
endif::VK_EXT_fragment_density_map[]
ifdef::VK_KHR_fragment_shading_rate[]
  * ename:VK_ACCESS_2_FRAGMENT_SHADING_RATE_ATTACHMENT_READ_BIT_KHR
    specifies read access to a fragment shading rate attachment during
    rasterization.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_FRAGMENT_SHADING_RATE_ATTACHMENT_BIT_KHR
    pipeline stage.
endif::VK_KHR_fragment_shading_rate[]
ifdef::VK_NV_shading_rate_image[]
  * ename:VK_ACCESS_2_SHADING_RATE_IMAGE_READ_BIT_NV specifies read access
    to a shading rate image during rasterization.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_2_SHADING_RATE_IMAGE_BIT_NV pipeline stage.
ifdef::VK_KHR_fragment_shading_rate[]
    It is equivalent to
    ename:VK_ACCESS_2_FRAGMENT_SHADING_RATE_ATTACHMENT_READ_BIT_KHR.
endif::VK_KHR_fragment_shading_rate[]
endif::VK_NV_shading_rate_image[]
ifdef::VK_KHR_video_decode_queue[]
  * ename:VK_ACCESS_2_VIDEO_DECODE_READ_BIT_KHR specifies read access to an
    image or buffer resource as part of a <<video-decode-operations, video
    decode operation>>.
    Such access occurs in the ename:VK_PIPELINE_STAGE_2_VIDEO_DECODE_BIT_KHR
    pipeline stage.
  * ename:VK_ACCESS_2_VIDEO_DECODE_WRITE_BIT_KHR specifies write access to
    an image or buffer resource as part of a <<video-decode-operations,
    video decode operation>>.
    Such access occurs in the ename:VK_PIPELINE_STAGE_2_VIDEO_DECODE_BIT_KHR
    pipeline stage.
endif::VK_KHR_video_decode_queue[]
ifdef::VK_KHR_video_encode_queue[]
  * ename:VK_ACCESS_2_VIDEO_ENCODE_READ_BIT_KHR specifies read access to an
    image or buffer resource as part of a <<video-encode-operations, video
    encode operation>>.
    Such access occurs in the ename:VK_PIPELINE_STAGE_2_VIDEO_ENCODE_BIT_KHR
    pipeline stage.
  * ename:VK_ACCESS_2_VIDEO_ENCODE_WRITE_BIT_KHR specifies write access to
    an image or buffer resource as part of a <<video-encode-operations,
    video encode operation>>.
    Such access occurs in the ename:VK_PIPELINE_STAGE_2_VIDEO_ENCODE_BIT_KHR
    pipeline stage.
endif::VK_KHR_video_encode_queue[]

[NOTE]
.Note
====
In situations where an application wishes to select all access types for a
given set of pipeline stages, ename:VK_ACCESS_2_MEMORY_READ_BIT_KHR or
ename:VK_ACCESS_2_MEMORY_WRITE_BIT_KHR can be used.
This is particularly useful when specifying stages that only have a single
access type.
====

[NOTE]
.Note
====
The tname:VkAccessFlags2KHR bitmask goes beyond the 31 individual bit flags
allowable within a C99 enum, which is how elink:VkAccessFlagBits is defined.
The first 31 values are common to both, and are interchangeable.
====
--

[open,refpage='VkAccessFlags2KHR',desc='64-bit mask of access flags',type='flags']
--
tname:VkAccessFlags2KHR is a bitmask type for setting a mask of zero or more
elink:VkAccessFlagBits2KHR:

include::{generated}/api/flags/VkAccessFlags2KHR.txt[]
--
endif::VK_KHR_synchronization2[]

[open,refpage='VkAccessFlagBits',desc='Bitmask specifying memory access types that will participate in a memory dependency',type='enums']
--
Bits which can: be set in the pname:srcAccessMask and pname:dstAccessMask
members of slink:VkSubpassDependency,
ifdef::VK_KHR_synchronization2[slink:VkSubpassDependency2,]
slink:VkMemoryBarrier, slink:VkBufferMemoryBarrier, and
slink:VkImageMemoryBarrier, specifying access behavior, are:

include::{generated}/api/enums/VkAccessFlagBits.txt[]

ifdef::VK_KHR_synchronization2[]
These values all have the same meaning as the equivalently named values for
tlink:VkAccessFlags2KHR.

  * ename:VK_ACCESS_NONE_KHR specifies no accesses.
endif::VK_KHR_synchronization2[]
  * ename:VK_ACCESS_MEMORY_READ_BIT specifies all read accesses.
    It is always valid in any access mask, and is treated as equivalent to
    setting all etext:READ access flags that are valid where it is used.
  * ename:VK_ACCESS_MEMORY_WRITE_BIT specifies all write accesses.
    It is always valid in any access mask, and is treated as equivalent to
    setting all etext:WRITE access flags that are valid where it is used.
  * ename:VK_ACCESS_INDIRECT_COMMAND_READ_BIT specifies read access to
    indirect command data read as part of an indirect
ifdef::VK_KHR_acceleration_structure[build,]
ifdef::VK_KHR_ray_tracing_pipeline[trace,]
    drawing or dispatching command.
    Such access occurs in the ename:VK_PIPELINE_STAGE_DRAW_INDIRECT_BIT
    pipeline stage.
  * ename:VK_ACCESS_INDEX_READ_BIT specifies read access to an index buffer
    as part of an indexed drawing command, bound by
    flink:vkCmdBindIndexBuffer.
    Such access occurs in the ename:VK_PIPELINE_STAGE_VERTEX_INPUT_BIT
    pipeline stage.
  * ename:VK_ACCESS_VERTEX_ATTRIBUTE_READ_BIT specifies read access to a
    vertex buffer as part of a drawing command, bound by
    flink:vkCmdBindVertexBuffers.
    Such access occurs in the ename:VK_PIPELINE_STAGE_VERTEX_INPUT_BIT
    pipeline stage.
  * ename:VK_ACCESS_UNIFORM_READ_BIT specifies read access to a
    <<descriptorsets-uniformbuffer, uniform buffer>> in any shader pipeline
    stage.
  * ename:VK_ACCESS_INPUT_ATTACHMENT_READ_BIT specifies read access to an
    <<renderpass, input attachment>> within a render pass during
ifdef::VK_HUAWEI_subpass_shading[]
    subpass shading or
endif::VK_HUAWEI_subpass_shading[]
    fragment shading.
    Such access occurs in the
ifdef::VK_HUAWEI_subpass_shading[]
    ename:VK_PIPELINE_STAGE_2_SUBPASS_SHADING_BIT_HUAWEI or
endif::VK_HUAWEI_subpass_shading[]
    ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT pipeline stage.
  * ename:VK_ACCESS_SHADER_READ_BIT specifies read access to a
    <<descriptorsets-uniformbuffer, uniform buffer>>,
    <<descriptorsets-uniformtexelbuffer, uniform texel buffer>>,
    <<descriptorsets-sampledimage, sampled image>>,
    <<descriptorsets-storagebuffer, storage buffer>>,
ifdef::VK_VERSION_1_2,VK_EXT_buffer_device_address,VK_KHR_buffer_device_address[]
    <<descriptorsets-physical-storage-buffer, physical storage buffer>>,
endif::VK_VERSION_1_2,VK_EXT_buffer_device_address,VK_KHR_buffer_device_address[]
ifdef::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
    <<shader-binding-table, shader binding table>>,
endif::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
    <<descriptorsets-storagetexelbuffer, storage texel buffer>>, or
    <<descriptorsets-storageimage, storage image>> in any shader pipeline
    stage.
  * ename:VK_ACCESS_SHADER_WRITE_BIT specifies write access to a
    <<descriptorsets-storagebuffer, storage buffer>>,
ifdef::VK_VERSION_1_2,VK_EXT_buffer_device_address,VK_KHR_buffer_device_address[]
    <<descriptorsets-physical-storage-buffer, physical storage buffer>>,
endif::VK_VERSION_1_2,VK_EXT_buffer_device_address,VK_KHR_buffer_device_address[]
    <<descriptorsets-storagetexelbuffer, storage texel buffer>>, or
    <<descriptorsets-storageimage, storage image>> in any shader pipeline
    stage.
  * ename:VK_ACCESS_COLOR_ATTACHMENT_READ_BIT specifies read access to a
    <<renderpass, color attachment>>, such as via <<framebuffer-blending,
    blending>>, <<framebuffer-logicop, logic operations>>, or via certain
    <<renderpass-load-store-ops, subpass load operations>>.
ifdef::VK_EXT_blend_operation_advanced[]
    It does not include <<framebuffer-blend-advanced, advanced blend
    operations>>.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT pipeline stage.
endif::VK_EXT_blend_operation_advanced[]
  * ename:VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT specifies write access to a
ifndef::VK_VERSION_1_2,VK_KHR_depth_stencil_resolve[]
    <<renderpass, color or resolve attachment>>
endif::VK_VERSION_1_2,VK_KHR_depth_stencil_resolve[]
ifdef::VK_VERSION_1_2,VK_KHR_depth_stencil_resolve[]
    <<renderpass, color, resolve, or depth/stencil resolve attachment>>
endif::VK_VERSION_1_2,VK_KHR_depth_stencil_resolve[]
    during a <<renderpass, render pass>> or via certain
    <<renderpass-load-store-ops, subpass load and store operations>>.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT pipeline stage.
  * ename:VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_READ_BIT specifies read access
    to a <<renderpass, depth/stencil attachment>>, via <<fragops-ds-state,
    depth or stencil operations>> or via certain
    <<renderpass-load-store-ops, subpass load operations>>.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT or
    ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT pipeline stages.
  * ename:VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT specifies write
    access to a <<renderpass, depth/stencil attachment>>, via
    <<fragops-ds-state, depth or stencil operations>> or via certain
    <<renderpass-load-store-ops, subpass load and store operations>>.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT or
    ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT pipeline stages.
  * ename:VK_ACCESS_TRANSFER_READ_BIT specifies read access to an image or
    buffer in a <<copies, copy>> operation.
ifdef::VK_KHR_synchronization2[]
    Such access occurs in the ename:VK_PIPELINE_STAGE_2_ALL_TRANSFER_BIT_KHR
    pipeline stage.
endif::VK_KHR_synchronization2[]
  * ename:VK_ACCESS_TRANSFER_WRITE_BIT specifies write access to an image or
    buffer in a <<clears, clear>> or <<copies, copy>> operation.
ifdef::VK_KHR_synchronization2[]
    Such access occurs in the ename:VK_PIPELINE_STAGE_2_ALL_TRANSFER_BIT_KHR
    pipeline stage.
endif::VK_KHR_synchronization2[]
  * ename:VK_ACCESS_HOST_READ_BIT specifies read access by a host operation.
    Accesses of this type are not performed through a resource, but directly
    on memory.
    Such access occurs in the ename:VK_PIPELINE_STAGE_HOST_BIT pipeline
    stage.
  * ename:VK_ACCESS_HOST_WRITE_BIT specifies write access by a host
    operation.
    Accesses of this type are not performed through a resource, but directly
    on memory.
    Such access occurs in the ename:VK_PIPELINE_STAGE_HOST_BIT pipeline
    stage.
ifdef::VK_EXT_conditional_rendering[]
  * ename:VK_ACCESS_CONDITIONAL_RENDERING_READ_BIT_EXT specifies read access
    to a predicate as part of conditional rendering.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_CONDITIONAL_RENDERING_BIT_EXT pipeline stage.
endif::VK_EXT_conditional_rendering[]
ifdef::VK_EXT_transform_feedback[]
  * ename:VK_ACCESS_TRANSFORM_FEEDBACK_WRITE_BIT_EXT specifies write access
    to a transform feedback buffer made when transform feedback is active.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_TRANSFORM_FEEDBACK_BIT_EXT pipeline stage.
  * ename:VK_ACCESS_TRANSFORM_FEEDBACK_COUNTER_READ_BIT_EXT specifies read
    access to a transform feedback counter buffer which is read when
    fname:vkCmdBeginTransformFeedbackEXT executes.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_TRANSFORM_FEEDBACK_BIT_EXT pipeline stage.
  * ename:VK_ACCESS_TRANSFORM_FEEDBACK_COUNTER_WRITE_BIT_EXT specifies write
    access to a transform feedback counter buffer which is written when
    fname:vkCmdEndTransformFeedbackEXT executes.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_TRANSFORM_FEEDBACK_BIT_EXT pipeline stage.
endif::VK_EXT_transform_feedback[]
ifdef::VK_NV_device_generated_commands[]
  * ename:VK_ACCESS_COMMAND_PREPROCESS_READ_BIT_NV specifies reads from
    buffer inputs to flink:vkCmdPreprocessGeneratedCommandsNV.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_COMMAND_PREPROCESS_BIT_NV pipeline stage.
  * ename:VK_ACCESS_COMMAND_PREPROCESS_WRITE_BIT_NV specifies writes to the
    target command buffer:VkBuffer preprocess outputs in
    flink:vkCmdPreprocessGeneratedCommandsNV.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_COMMAND_PREPROCESS_BIT_NV pipeline stage.
endif::VK_NV_device_generated_commands[]
ifdef::VK_EXT_blend_operation_advanced[]
  * ename:VK_ACCESS_COLOR_ATTACHMENT_READ_NONCOHERENT_BIT_EXT specifies read
    access to <<renderpass, color attachments>>, including
    <<framebuffer-blend-advanced,advanced blend operations>>.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT pipeline stage.
endif::VK_EXT_blend_operation_advanced[]
ifdef::VK_KHR_acceleration_structure,VK_NV_ray_tracing[]
ifdef::VK_HUAWEI_invocation_mask[]
  * ename:VK_ACCESS_2_INVOCATION_MASK_READ_BIT_HUAWEI specifies read access
    to a invocation mask image in the
    ename:VK_PIPELINE_STAGE_2_INVOCATION_MASK_BIT_HUAWEI pipeline stage.
endif::VK_HUAWEI_invocation_mask[]
  * ename:VK_ACCESS_ACCELERATION_STRUCTURE_READ_BIT_KHR specifies read
    access to an acceleration structure as part of a trace, build, or copy
    command, or to an <<acceleration-structure-scratch, acceleration
    structure scratch buffer>> as part of a build command.
    Such access occurs in the
ifdef::VK_KHR_ray_tracing_pipeline[]
    ename:VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR pipeline stage or
endif::VK_KHR_ray_tracing_pipeline[]
    ename:VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR pipeline
    stage.
  * ename:VK_ACCESS_ACCELERATION_STRUCTURE_WRITE_BIT_KHR specifies write
    access to an acceleration structure or <<acceleration-structure-scratch,
    acceleration structure scratch buffer>> as part of a build or copy
    command.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR pipeline
    stage.
endif::VK_KHR_acceleration_structure,VK_NV_ray_tracing[]
ifdef::VK_EXT_fragment_density_map[]
  * ename:VK_ACCESS_FRAGMENT_DENSITY_MAP_READ_BIT_EXT specifies read access
    to a <<renderpass-fragmentdensitymapattachment, fragment density map
    attachment>> during dynamic <<fragmentdensitymapops, fragment density
    map operations>> Such access occurs in the
    ename:VK_PIPELINE_STAGE_FRAGMENT_DENSITY_PROCESS_BIT_EXT pipeline stage.
endif::VK_EXT_fragment_density_map[]
ifdef::VK_KHR_fragment_shading_rate[]
  * ename:VK_ACCESS_FRAGMENT_SHADING_RATE_ATTACHMENT_READ_BIT_KHR specifies
    read access to a fragment shading rate attachment during rasterization.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_FRAGMENT_SHADING_RATE_ATTACHMENT_BIT_KHR
    pipeline stage.
endif::VK_KHR_fragment_shading_rate[]
ifdef::VK_NV_shading_rate_image[]
  * ename:VK_ACCESS_SHADING_RATE_IMAGE_READ_BIT_NV specifies read access to
    a shading rate image during rasterization.
    Such access occurs in the
    ename:VK_PIPELINE_STAGE_SHADING_RATE_IMAGE_BIT_NV pipeline stage.
ifdef::VK_KHR_fragment_shading_rate[]
    It is equivalent to
    ename:VK_PIPELINE_STAGE_FRAGMENT_SHADING_RATE_ATTACHMENT_BIT_KHR.
endif::VK_KHR_fragment_shading_rate[]
endif::VK_NV_shading_rate_image[]

Certain access types are only performed by a subset of pipeline stages.
Any synchronization command that takes both stage masks and access masks
uses both to define the <<synchronization-dependencies-access-scopes, access
scopes>> - only the specified access types performed by the specified stages
are included in the access scope.
An application must: not specify an access flag in a synchronization command
if it does not include a pipeline stage in the corresponding stage mask that
is able to perform accesses of that type.
The following table lists, for each access flag, which pipeline stages can:
perform that type of access.

[[synchronization-access-types-supported]]
.Supported access types
[cols="50,50",options="header"]
|====
|Access flag                                                  | Supported pipeline stages
|ename:VK_ACCESS_INDIRECT_COMMAND_READ_BIT                    | ename:VK_PIPELINE_STAGE_DRAW_INDIRECT_BIT
ifdef::VK_KHR_acceleration_structure[]
, ename:VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR
endif::VK_KHR_acceleration_structure[]
|ename:VK_ACCESS_INDEX_READ_BIT                               | ename:VK_PIPELINE_STAGE_VERTEX_INPUT_BIT
|ename:VK_ACCESS_VERTEX_ATTRIBUTE_READ_BIT                    | ename:VK_PIPELINE_STAGE_VERTEX_INPUT_BIT

|ename:VK_ACCESS_UNIFORM_READ_BIT                             |
ifdef::VK_NV_mesh_shader[]
                                                               ename:VK_PIPELINE_STAGE_TASK_SHADER_BIT_NV, ename:VK_PIPELINE_STAGE_MESH_SHADER_BIT_NV,
endif::VK_NV_mesh_shader[]
ifdef::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
                                                               ename:VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR,
endif::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
                                                               ename:VK_PIPELINE_STAGE_VERTEX_SHADER_BIT, ename:VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT, ename:VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT, ename:VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT, ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT, or ename:VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT

|ename:VK_ACCESS_SHADER_READ_BIT                              |
ifdef::VK_KHR_acceleration_structure[]
                                                               ename:VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR,
endif::VK_KHR_acceleration_structure[]
ifdef::VK_NV_mesh_shader[]
                                                               ename:VK_PIPELINE_STAGE_TASK_SHADER_BIT_NV, ename:VK_PIPELINE_STAGE_MESH_SHADER_BIT_NV,
endif::VK_NV_mesh_shader[]
ifdef::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
                                                               ename:VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR,
endif::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
                                                               ename:VK_PIPELINE_STAGE_VERTEX_SHADER_BIT, ename:VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT, ename:VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT, ename:VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT, ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT, or ename:VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT

|ename:VK_ACCESS_SHADER_WRITE_BIT                             |
ifdef::VK_NV_mesh_shader[]
                                                               ename:VK_PIPELINE_STAGE_TASK_SHADER_BIT_NV, ename:VK_PIPELINE_STAGE_MESH_SHADER_BIT_NV,
endif::VK_NV_mesh_shader[]
ifdef::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
                                                               ename:VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR,
endif::VK_NV_ray_tracing,VK_KHR_ray_tracing_pipeline[]
                                                               ename:VK_PIPELINE_STAGE_VERTEX_SHADER_BIT, ename:VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT, ename:VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT, ename:VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT, ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT, or ename:VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT

|ename:VK_ACCESS_INPUT_ATTACHMENT_READ_BIT                    |
ifdef::VK_HUAWEI_subpass_shading[]
                                                               ename:VK_PIPELINE_STAGE_2_SUBPASS_SHADING_BIT_HUAWEI, or
endif::VK_HUAWEI_subpass_shading[]
                                                               ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT
|ename:VK_ACCESS_COLOR_ATTACHMENT_READ_BIT                    | ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT
|ename:VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT                   | ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT
|ename:VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_READ_BIT            | ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT, or ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT
|ename:VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT           | ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT, or ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT
|ename:VK_ACCESS_TRANSFER_READ_BIT                            | ename:VK_PIPELINE_STAGE_TRANSFER_BIT
ifdef::VK_KHR_acceleration_structure[or ename:VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR]
|ename:VK_ACCESS_TRANSFER_WRITE_BIT                           | ename:VK_PIPELINE_STAGE_TRANSFER_BIT
ifdef::VK_KHR_acceleration_structure[or ename:VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR]
|ename:VK_ACCESS_HOST_READ_BIT                                | ename:VK_PIPELINE_STAGE_HOST_BIT
|ename:VK_ACCESS_HOST_WRITE_BIT                               | ename:VK_PIPELINE_STAGE_HOST_BIT
|ename:VK_ACCESS_MEMORY_READ_BIT                              | Any
|ename:VK_ACCESS_MEMORY_WRITE_BIT                             | Any
ifdef::VK_EXT_blend_operation_advanced[]
|ename:VK_ACCESS_COLOR_ATTACHMENT_READ_NONCOHERENT_BIT_EXT    | ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT
endif::VK_EXT_blend_operation_advanced[]
ifdef::VK_NV_device_generated_commands[]
|ename:VK_ACCESS_COMMAND_PREPROCESS_READ_BIT_NV               | ename:VK_PIPELINE_STAGE_COMMAND_PREPROCESS_BIT_NV
|ename:VK_ACCESS_COMMAND_PREPROCESS_WRITE_BIT_NV              | ename:VK_PIPELINE_STAGE_COMMAND_PREPROCESS_BIT_NV
endif::VK_NV_device_generated_commands[]
ifdef::VK_EXT_conditional_rendering[]
|ename:VK_ACCESS_CONDITIONAL_RENDERING_READ_BIT_EXT           | ename:VK_PIPELINE_STAGE_CONDITIONAL_RENDERING_BIT_EXT
endif::VK_EXT_conditional_rendering[]
ifdef::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
|ename:VK_ACCESS_FRAGMENT_SHADING_RATE_ATTACHMENT_READ_BIT_KHR | ename:VK_PIPELINE_STAGE_FRAGMENT_SHADING_RATE_ATTACHMENT_BIT_KHR
endif::VK_KHR_fragment_shading_rate,VK_NV_shading_rate_image[]
ifdef::VK_HUAWEI_invocation_mask[]
|ename:VK_ACCESS_2_INVOCATION_MASK_READ_BIT_HUAWEI                           | ename:VK_PIPELINE_STAGE_2_INVOCATION_MASK_BIT_HUAWEI
endif::VK_HUAWEI_invocation_mask[]
ifdef::VK_EXT_transform_feedback[]
|ename:VK_ACCESS_TRANSFORM_FEEDBACK_WRITE_BIT_EXT             | ename:VK_PIPELINE_STAGE_TRANSFORM_FEEDBACK_BIT_EXT
|ename:VK_ACCESS_TRANSFORM_FEEDBACK_COUNTER_WRITE_BIT_EXT     | ename:VK_PIPELINE_STAGE_TRANSFORM_FEEDBACK_BIT_EXT
|ename:VK_ACCESS_TRANSFORM_FEEDBACK_COUNTER_READ_BIT_EXT      | ename:VK_PIPELINE_STAGE_TRANSFORM_FEEDBACK_BIT_EXT, ename:VK_PIPELINE_STAGE_DRAW_INDIRECT_BIT
endif::VK_EXT_transform_feedback[]
ifdef::VK_NV_ray_tracing,VK_KHR_acceleration_structure[]
|ename:VK_ACCESS_ACCELERATION_STRUCTURE_READ_BIT_KHR          |
ifdef::VK_KHR_ray_query[]
ifdef::VK_NV_mesh_shader[]
                                                               ename:VK_PIPELINE_STAGE_TASK_SHADER_BIT_NV, ename:VK_PIPELINE_STAGE_MESH_SHADER_BIT_NV,
endif::VK_NV_mesh_shader[]
                                                               ename:VK_PIPELINE_STAGE_VERTEX_SHADER_BIT, ename:VK_PIPELINE_STAGE_TESSELLATION_CONTROL_SHADER_BIT, ename:VK_PIPELINE_STAGE_TESSELLATION_EVALUATION_SHADER_BIT, ename:VK_PIPELINE_STAGE_GEOMETRY_SHADER_BIT, ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT, ename:VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT,
endif::VK_KHR_ray_query[]
ifdef::VK_KHR_ray_tracing_pipeline[]
ename:VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR,
endif::VK_KHR_ray_tracing_pipeline[]
ifdef::VK_KHR_ray_tracing_pipeline,VK_KHR_ray_query[]
 or
endif::VK_KHR_ray_tracing_pipeline,VK_KHR_ray_query[]
ename:VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR
|ename:VK_ACCESS_ACCELERATION_STRUCTURE_WRITE_BIT_KHR         | ename:VK_PIPELINE_STAGE_ACCELERATION_STRUCTURE_BUILD_BIT_KHR
endif::VK_NV_ray_tracing,VK_KHR_acceleration_structure[]
ifdef::VK_EXT_fragment_density_map[]
|ename:VK_ACCESS_FRAGMENT_DENSITY_MAP_READ_BIT_EXT            | ename:VK_PIPELINE_STAGE_FRAGMENT_DENSITY_PROCESS_BIT_EXT
endif::VK_EXT_fragment_density_map[]
|====
--

[open,refpage='VkAccessFlags',desc='Bitmask of VkAccessFlagBits',type='flags']
--
include::{generated}/api/flags/VkAccessFlags.txt[]

tname:VkAccessFlags is a bitmask type for setting a mask of zero or more
elink:VkAccessFlagBits.
--


[[synchronization-host-access-types]]
If a memory object does not have the
ename:VK_MEMORY_PROPERTY_HOST_COHERENT_BIT property, then
flink:vkFlushMappedMemoryRanges must: be called in order to guarantee that
writes to the memory object from the host are made available to the host
domain, where they can: be further made available to the device domain via a
domain operation.
Similarly, flink:vkInvalidateMappedMemoryRanges must: be called to guarantee
that writes which are available to the host domain are made visible to host
operations.

If the memory object does have the
ename:VK_MEMORY_PROPERTY_HOST_COHERENT_BIT property flag, writes to the
memory object from the host are automatically made available to the host
domain.
Similarly, writes made available to the host domain are automatically made
visible to the host.

[NOTE]
.Note
====
<<devsandqueues-submission, Queue submission commands>> automatically
perform a <<synchronization-submission-host-writes,domain operation from
host to device>> for all writes performed before the command executes, so in
most cases an explicit memory barrier is not needed for this case.
In the few circumstances where a submit does not occur between the host
write and the device read access, writes can: be made available by using an
explicit memory barrier.
====


[[synchronization-framebuffer-regions]]
=== Framebuffer Region Dependencies

<<synchronization-pipeline-stages, Pipeline stages>> that operate on, or
with respect to, the framebuffer are collectively the _framebuffer-space_
pipeline stages.
These stages are:

  * ename:VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT
  * ename:VK_PIPELINE_STAGE_EARLY_FRAGMENT_TESTS_BIT
  * ename:VK_PIPELINE_STAGE_LATE_FRAGMENT_TESTS_BIT
  * ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT

For these pipeline stages, an execution or memory dependency from the first
set of operations to the second set can: either be a single
_framebuffer-global_ dependency, or split into multiple _framebuffer-local_
dependencies.
A dependency with non-framebuffer-space pipeline stages is neither
framebuffer-global nor framebuffer-local.

ifndef::VK_QCOM_render_pass_shader_resolve[]
A _framebuffer region_ is a set of sample (x, y, layer, sample) coordinates
that is a subset of the entire framebuffer.
endif::VK_QCOM_render_pass_shader_resolve[]
ifdef::VK_QCOM_render_pass_shader_resolve[]
A _framebuffer region_ is a subset of the entire framebuffer, and can:
either be:

 * A _sample region_, which is set of sample (x, y, layer, sample)
   coordinates that is a subset of the entire framebuffer, or

 * A _fragment region_, which is a set of fragment (x, y, layer) coordinates
   that is a subset of the entire framebuffer.
endif::VK_QCOM_render_pass_shader_resolve[]

Both <<synchronization-dependencies-scopes, synchronization scopes>> of a
framebuffer-local dependency include only the operations performed within
corresponding framebuffer regions (as defined below).
No ordering guarantees are made between different framebuffer regions for a
framebuffer-local dependency.

Both <<synchronization-dependencies-scopes, synchronization scopes>> of a
framebuffer-global dependency include operations on all framebuffer-regions.

If the first synchronization scope includes operations on pixels/fragments
with N samples and the second synchronization scope includes operations on
pixels/fragments with M samples, where N does not equal M, then a
framebuffer region containing all samples at a given (x, y, layer)
coordinate in the first synchronization scope corresponds to a region
containing all samples at the same coordinate in the second synchronization
scope.
ifndef::VK_QCOM_render_pass_shader_resolve[]
In other words, it is a pixel granularity dependency.
endif::VK_QCOM_render_pass_shader_resolve[]
ifdef::VK_QCOM_render_pass_shader_resolve[]
In other words, the framebuffer region is a fragment region and it is a
pixel granularity dependency.
endif::VK_QCOM_render_pass_shader_resolve[]
If N equals M,
ifdef::VK_QCOM_render_pass_shader_resolve[]
and if the sname:VkSubpassDescription::pname:flags does not specify the
ename:VK_SUBPASS_DESCRIPTION_FRAGMENT_REGION_BIT_QCOM flag,
endif::VK_QCOM_render_pass_shader_resolve[]
then a framebuffer region containing a single (x, y, layer, sample)
coordinate in the first synchronization scope corresponds to a region
containing the same sample at the same coordinate in the second
synchronization scope.
ifndef::VK_QCOM_render_pass_shader_resolve[]
In other words, it is a sample granularity dependency.
endif::VK_QCOM_render_pass_shader_resolve[]
ifdef::VK_QCOM_render_pass_shader_resolve[]
In other words, the framebuffer region is a sample region and it is a sample
granularity dependency.
endif::VK_QCOM_render_pass_shader_resolve[]

[NOTE]
.Note
====
Since fragment shader invocations are not specified to run in any particular
groupings, the size of a framebuffer region is implementation-dependent, not
known to the application, and must: be assumed to be no larger than
specified above.
====

[NOTE]
.Note
====
Practically, the pixel vs sample granularity dependency means that if an
input attachment has a different number of samples than the pipeline's
pname:rasterizationSamples, then a fragment can: access any sample in the
input attachment's pixel even if it only uses framebuffer-local
dependencies.
If the input attachment has the same number of samples, then the fragment
can: only access the covered samples in its input code:SampleMask (i.e. the
fragment operations happen-after a framebuffer-local dependency for each
sample the fragment covers).
To access samples that are not covered,
ifdef::VK_QCOM_render_pass_shader_resolve[]
either the sname:VkSubpassDescription::pname:flags
ename:VK_SUBPASS_DESCRIPTION_FRAGMENT_REGION_BIT_QCOM flag is required, or
endif::VK_QCOM_render_pass_shader_resolve[]
a framebuffer-global dependency is required.
====

If a synchronization command includes a pname:dependencyFlags parameter, and
specifies the ename:VK_DEPENDENCY_BY_REGION_BIT flag, then it defines
framebuffer-local dependencies for the framebuffer-space pipeline stages in
that synchronization command, for all framebuffer regions.
If no pname:dependencyFlags parameter is included, or the
ename:VK_DEPENDENCY_BY_REGION_BIT flag is not specified, then a
framebuffer-global dependency is specified for those stages.
The ename:VK_DEPENDENCY_BY_REGION_BIT flag does not affect the dependencies
between non-framebuffer-space pipeline stages, nor does it affect the
dependencies between framebuffer-space and non-framebuffer-space pipeline
stages.

[NOTE]
.Note
====
Framebuffer-local dependencies are more efficient for most architectures;
particularly tile-based architectures - which can keep framebuffer-regions
entirely in on-chip registers and thus avoid external bandwidth across such
a dependency.
Including a framebuffer-global dependency in your rendering will usually
force all implementations to flush data to memory, or to a higher level
cache, breaking any potential locality optimizations.
====


ifdef::VK_VERSION_1_1,VK_KHR_multiview[]
[[synchronization-view-local-dependencies]]
=== View-Local Dependencies

In a render pass instance that has <<renderpass-multiview,multiview>>
enabled, dependencies can: be either view-local or view-global.

A view-local dependency only includes operations from a single
<<renderpass-multiview-view-local,source view>> from the source subpass in
the first synchronization scope, and only includes operations from a single
<<renderpass-multiview-view-local,destination view>> from the destination
subpass in the second synchronization scope.
A view-global dependency includes all views in the view mask of the source
and destination subpasses in the corresponding synchronization scopes.

If a synchronization command includes a pname:dependencyFlags parameter and
specifies the ename:VK_DEPENDENCY_VIEW_LOCAL_BIT flag, then it defines
view-local dependencies for that synchronization command, for all views.
If no pname:dependencyFlags parameter is included or the
ename:VK_DEPENDENCY_VIEW_LOCAL_BIT flag is not specified, then a view-global
dependency is specified.
endif::VK_VERSION_1_1,VK_KHR_multiview[]


ifdef::VK_VERSION_1_1,VK_KHR_device_group[]
[[synchronization-device-local-dependencies]]
=== Device-Local Dependencies

Dependencies can: be either device-local or non-device-local.
A device-local dependency acts as multiple separate dependencies, one for
each physical device that executes the synchronization command, where each
dependency only includes operations from that physical device in both
synchronization scopes.
A non-device-local dependency is a single dependency where both
synchronization scopes include operations from all physical devices that
participate in the synchronization command.
For subpass dependencies, all physical devices in the
slink:VkDeviceGroupRenderPassBeginInfo::pname:deviceMask participate in the
dependency, and for pipeline barriers all physical devices that are set in
the command buffer's current device mask participate in the dependency.

If a synchronization command includes a pname:dependencyFlags parameter and
specifies the ename:VK_DEPENDENCY_DEVICE_GROUP_BIT flag, then it defines a
non-device-local dependency for that synchronization command.
If no pname:dependencyFlags parameter is included or the
ename:VK_DEPENDENCY_DEVICE_GROUP_BIT flag is not specified, then it defines
device-local dependencies for that synchronization command, for all
participating physical devices.

Semaphore and event dependencies are device-local and only execute on the
one physical device that performs the dependency.
endif::VK_VERSION_1_1,VK_KHR_device_group[]


[[synchronization-implicit]]
== Implicit Synchronization Guarantees

A small number of implicit ordering guarantees are provided by Vulkan,
ensuring that the order in which commands are submitted is meaningful, and
avoiding unnecessary complexity in common operations.

[[synchronization-submission-order]]
_Submission order_ is a fundamental ordering in Vulkan, giving meaning to
the order in which <<fundamentals-queueoperation-command-types, action and
synchronization commands>> are recorded and submitted to a single queue.
Explicit and implicit ordering guarantees between commands in Vulkan all
work on the premise that this ordering is meaningful.
This order does not itself define any execution or memory dependencies;
synchronization commands and other orderings within the API use this
ordering to define their scopes.

Submission order for any given set of commands is based on the order in
which they were recorded to command buffers and then submitted.
This order is determined as follows:

  . The initial order is determined by the order in which
    flink:vkQueueSubmit
ifdef::VK_KHR_synchronization2[]
    and flink:vkQueueSubmit2KHR
endif::VK_KHR_synchronization2[]
    commands are executed on the host, for a single queue, from first to
    last.
  . The order in which slink:VkSubmitInfo structures are specified in the
    pname:pSubmits parameter of flink:vkQueueSubmit,
ifdef::VK_KHR_synchronization2[]
    or in which slink:VkSubmitInfo2KHR structures are specified in the
    pname:pSubmits parameter of flink:vkQueueSubmit2KHR,
endif::VK_KHR_synchronization2[]
    from lowest index to highest.
  . The order in which command buffers are specified in the
    pname:pCommandBuffers member of slink:VkSubmitInfo
ifdef::VK_KHR_synchronization2[]
    or slink:VkSubmitInfo2KHR
endif::VK_KHR_synchronization2[]
    from lowest index to highest.
  . The order in which commands were recorded to a command buffer on the
    host, from first to last:
  ** For commands recorded outside a render pass, this includes all other
     commands recorded outside a render pass, including
     flink:vkCmdBeginRenderPass and flink:vkCmdEndRenderPass commands; it
     does not directly include commands inside a render pass.
  ** For commands recorded inside a render pass, this includes all other
     commands recorded inside the same subpass, including the
     flink:vkCmdBeginRenderPass and flink:vkCmdEndRenderPass commands that
     delimit the same render pass instance; it does not include commands
     recorded to other subpasses.
<<fundamentals-queueoperation-command-types, State commands>> do not execute
any operations on the device, instead they set the state of the command
buffer when they execute on the host, in the order that they are recorded.
<<fundamentals-queueoperation-command-types, Action commands>> consume the
current state of the command buffer when they are recorded, and will execute
state changes on the device as required to match the recorded state.

<<queries-order, Query commands>>, <<drawing-primitive-order, the order of
primitives passing through the graphics pipeline>> and
<<synchronization-image-barrier-layout-transition-order, image layout
transitions as part of an image memory barrier>> provide additional
guarantees based on submission order.

Execution of <<synchronization-pipeline-stages-order, pipeline stages>>
within a given command also has a loose ordering, dependent only on a single
command.

[[synchronization-signal-operation-order]]
_Signal operation order_ is a fundamental ordering in Vulkan, giving meaning
to the order in which semaphore and fence signal operations occur when
submitted to a single queue.
The signal operation order for queue operations is determined as follows:

  . The initial order is determined by the order in which
    flink:vkQueueSubmit
ifdef::VK_KHR_synchronization2[]
    and flink:vkQueueSubmit2KHR
endif::VK_KHR_synchronization2[]
    commands are executed on the host, for a single queue, from first to
    last.
  . The order in which slink:VkSubmitInfo structures are specified in the
    pname:pSubmits parameter of flink:vkQueueSubmit,
ifdef::VK_KHR_synchronization2[]
    or in which slink:VkSubmitInfo2KHR structures are specified in the
    pname:pSubmits parameter of flink:vkQueueSubmit2KHR,
endif::VK_KHR_synchronization2[]
    from lowest index to highest.
  . The fence signal operation defined by the pname:fence parameter of a
    flink:vkQueueSubmit,
ifdef::VK_KHR_synchronization2[]
    flink:vkQueueSubmit2KHR,
endif::VK_KHR_synchronization2[]
    or flink:vkQueueBindSparse command is ordered after all semaphore signal
    operations defined by that command.

Semaphore signal operations defined by a single slink:VkSubmitInfo,
ifdef::VK_KHR_synchronization2[]
slink:VkSubmitInfo2KHR,
endif::VK_KHR_synchronization2[]
or slink:VkBindSparseInfo structure are unordered with respect to other
semaphore signal operations defined within the same structure.

ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
The flink:vkSignalSemaphore command does not execute on a queue but instead
performs the signal operation from the host.
The semaphore signal operation defined by executing a
flink:vkSignalSemaphore command happens-after the flink:vkSignalSemaphore
command is invoked and happens-before the command returns.

[NOTE]
.Note
====
When signaling timeline semaphores, it is the responsibility of the
application to ensure that they are ordered such that the semaphore value is
strictly increasing.
Because the first synchronization scope for a semaphore signal operation
contains all semaphore signal operations which occur earlier in submission
order, all semaphore signal operations contained in any given batch are
guaranteed to happen-after all semaphore signal operations contained in any
previous batches.
However, no ordering guarantee is provided between the semaphore signal
operations defined within a single batch.
This, combined with the requirement that timeline semaphore values strictly
increase, means that it is invalid to signal the same timeline semaphore
twice within a single batch.

If an application wishes to ensure that some semaphore signal operation
happens-after some other semaphore signal operation, it can submit a
separate batch containing only semaphore signal operations, which will
happen-after the semaphore signal operations in any earlier batches.

When signaling a semaphore from the host, the only ordering guarantee is
that the signal operation happens-after when flink:vkSignalSemaphore is
called and happens-before it returns.
Therefore, it is invalid to call fname:vkSignalSemaphore while there are any
outstanding signal operations on that semaphore from any queue submissions
unless those queue submissions have some dependency which ensures that they
happen-after the host signal operation.
One example of this would be if the pending signal operation is, itself,
waiting on the same semaphore at a lower value and the call to
fname:vkSignalSemaphore signals that lower value.
Furthermore, if there are two or more processes or threads signaling the
same timeline semaphore from the host, the application must ensure that the
fname:vkSignalSemaphore with the lower semaphore value returns before
fname:vkSignalSemaphore is called with the higher value.
====
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]


[[synchronization-fences]]
== Fences

[open,refpage='VkFence',desc='Opaque handle to a fence object',type='handles']
--
Fences are a synchronization primitive that can: be used to insert a
dependency from a queue to the host.
Fences have two states - signaled and unsignaled.
A fence can: be signaled as part of the execution of a
<<devsandqueues-submission, queue submission>> command.
Fences can: be unsignaled on the host with flink:vkResetFences.
Fences can: be waited on by the host with the flink:vkWaitForFences command,
and the current state can: be queried with flink:vkGetFenceStatus.

ifdef::VK_VERSION_1_1,VK_KHR_external_fence[]
[[synchronization-fences-payloads]]
The internal data of a fence may: include a reference to any resources and
pending work associated with signal or unsignal operations performed on that
fence object, collectively referred to as the fence's _payload_.
Mechanisms to import and export that internal data to and from fences are
provided <<VkExportFenceCreateInfo, below>>.
These mechanisms indirectly enable applications to share fence state between
two or more fences and other synchronization primitives across process and
API boundaries.

endif::VK_VERSION_1_1,VK_KHR_external_fence[]

Fences are represented by sname:VkFence handles:

include::{generated}/api/handles/VkFence.txt[]
--

[open,refpage='vkCreateFence',desc='Create a new fence object',type='protos']
--
To create a fence, call:

include::{generated}/api/protos/vkCreateFence.txt[]

  * pname:device is the logical device that creates the fence.
  * pname:pCreateInfo is a pointer to a slink:VkFenceCreateInfo structure
    containing information about how the fence is to be created.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.
  * pname:pFence is a pointer to a handle in which the resulting fence
    object is returned.

include::{generated}/validity/protos/vkCreateFence.txt[]
--

[open,refpage='VkFenceCreateInfo',desc='Structure specifying parameters of a newly created fence',type='structs']
--
The sname:VkFenceCreateInfo structure is defined as:

include::{generated}/api/structs/VkFenceCreateInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:flags is a bitmask of elink:VkFenceCreateFlagBits specifying the
    initial state and behavior of the fence.

include::{generated}/validity/structs/VkFenceCreateInfo.txt[]
--

[open,refpage='VkFenceCreateFlagBits',desc='Bitmask specifying initial state and behavior of a fence',type='enums']
--
include::{generated}/api/enums/VkFenceCreateFlagBits.txt[]

  * ename:VK_FENCE_CREATE_SIGNALED_BIT specifies that the fence object is
    created in the signaled state.
    Otherwise, it is created in the unsignaled state.
--

[open,refpage='VkFenceCreateFlags',desc='Bitmask of VkFenceCreateFlagBits',type='flags']
--
include::{generated}/api/flags/VkFenceCreateFlags.txt[]

tname:VkFenceCreateFlags is a bitmask type for setting a mask of zero or
more elink:VkFenceCreateFlagBits.
--

ifdef::VK_VERSION_1_1,VK_KHR_external_fence[]
[open,refpage='VkExportFenceCreateInfo',desc='Structure specifying handle types that can be exported from a fence',type='structs']
--
To create a fence whose payload can: be exported to external handles, add a
slink:VkExportFenceCreateInfo structure to the pname:pNext chain of the
slink:VkFenceCreateInfo structure.
The sname:VkExportFenceCreateInfo structure is defined as:

include::{generated}/api/structs/VkExportFenceCreateInfo.txt[]

ifdef::VK_KHR_external_fence[]
or the equivalent

include::{generated}/api/structs/VkExportFenceCreateInfoKHR.txt[]
endif::VK_KHR_external_fence[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:handleTypes is a bitmask of
    elink:VkExternalFenceHandleTypeFlagBits specifying one or more fence
    handle types the application can: export from the resulting fence.
    The application can: request multiple handle types for the same fence.

.Valid Usage
****
  * [[VUID-VkExportFenceCreateInfo-handleTypes-01446]]
    The bits in pname:handleTypes must: be supported and compatible, as
    reported by slink:VkExternalFenceProperties
****

include::{generated}/validity/structs/VkExportFenceCreateInfo.txt[]
--
endif::VK_VERSION_1_1,VK_KHR_external_fence[]

ifdef::VK_KHR_external_fence_win32[]
[open,refpage='VkExportFenceWin32HandleInfoKHR',desc='Structure specifying additional attributes of Windows handles exported from a fence',type='structs']
--
To specify additional attributes of NT handles exported from a fence, add a
slink:VkExportFenceWin32HandleInfoKHR structure to the pname:pNext chain of
the slink:VkFenceCreateInfo structure.
The sname:VkExportFenceWin32HandleInfoKHR structure is defined as:

include::{generated}/api/structs/VkExportFenceWin32HandleInfoKHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:pAttributes is a pointer to a Windows code:SECURITY_ATTRIBUTES
    structure specifying security attributes of the handle.
  * pname:dwAccess is a code:DWORD specifying access rights of the handle.
  * pname:name is a null-terminated UTF-16 string to associate with the
    underlying synchronization primitive referenced by NT handles exported
    from the created fence.

If slink:VkExportFenceCreateInfo is not inluded in the same pname:pNext
chain, this structure is ignored.

If slink:VkExportFenceCreateInfo is included in the pname:pNext chain of
slink:VkFenceCreateInfo with a Windows pname:handleType, but either
sname:VkExportFenceWin32HandleInfoKHR is not included in the pname:pNext
chain, or if it is but pname:pAttributes is set to `NULL`, default security
descriptor values will be used, and child processes created by the
application will not inherit the handle, as described in the MSDN
documentation for "`Synchronization Object Security and Access Rights`"^1^.
Further, if the structure is not present, the access rights will be

code:DXGI_SHARED_RESOURCE_READ | code:DXGI_SHARED_RESOURCE_WRITE

for handles of the following types:

ename:VK_EXTERNAL_FENCE_HANDLE_TYPE_OPAQUE_WIN32_BIT

1::
    https://docs.microsoft.com/en-us/windows/win32/sync/synchronization-object-security-and-access-rights

.Valid Usage
****
  * [[VUID-VkExportFenceWin32HandleInfoKHR-handleTypes-01447]]
    If slink:VkExportFenceCreateInfo::pname:handleTypes does not include
    ename:VK_EXTERNAL_FENCE_HANDLE_TYPE_OPAQUE_WIN32_BIT, a
    sname:VkExportFenceWin32HandleInfoKHR structure must: not be included in
    the pname:pNext chain of slink:VkFenceCreateInfo
****

include::{generated}/validity/structs/VkExportFenceWin32HandleInfoKHR.txt[]
--

[open,refpage='vkGetFenceWin32HandleKHR',desc='Get a Windows HANDLE for a fence',type='protos']
--
To export a Windows handle representing the state of a fence, call:

include::{generated}/api/protos/vkGetFenceWin32HandleKHR.txt[]

  * pname:device is the logical device that created the fence being
    exported.
  * pname:pGetWin32HandleInfo is a pointer to a
    slink:VkFenceGetWin32HandleInfoKHR structure containing parameters of
    the export operation.
  * pname:pHandle will return the Windows handle representing the fence
    state.

For handle types defined as NT handles, the handles returned by
fname:vkGetFenceWin32HandleKHR are owned by the application.
To avoid leaking resources, the application must: release ownership of them
using the code:CloseHandle system call when they are no longer needed.

Exporting a Windows handle from a fence may: have side effects depending on
the transference of the specified handle type, as described in
<<synchronization-fences-importing,Importing Fence Payloads>>.

include::{generated}/validity/protos/vkGetFenceWin32HandleKHR.txt[]
--

[open,refpage='VkFenceGetWin32HandleInfoKHR',desc='Structure describing a Win32 handle fence export operation',type='structs']
--
The sname:VkFenceGetWin32HandleInfoKHR structure is defined as:

include::{generated}/api/structs/VkFenceGetWin32HandleInfoKHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:fence is the fence from which state will be exported.
  * pname:handleType is a elink:VkExternalFenceHandleTypeFlagBits value
    specifying the type of handle requested.

The properties of the handle returned depend on the value of
pname:handleType.
See elink:VkExternalFenceHandleTypeFlagBits for a description of the
properties of the defined external fence handle types.

.Valid Usage
****
  * [[VUID-VkFenceGetWin32HandleInfoKHR-handleType-01448]]
    pname:handleType must: have been included in
    slink:VkExportFenceCreateInfo::pname:handleTypes when the pname:fence's
    current payload was created
  * [[VUID-VkFenceGetWin32HandleInfoKHR-handleType-01449]]
    If pname:handleType is defined as an NT handle,
    flink:vkGetFenceWin32HandleKHR must: be called no more than once for
    each valid unique combination of pname:fence and pname:handleType
  * [[VUID-VkFenceGetWin32HandleInfoKHR-fence-01450]]
    pname:fence must: not currently have its payload replaced by an imported
    payload as described below in
    <<synchronization-fences-importing,Importing Fence Payloads>> unless
    that imported payload's handle type was included in
    slink:VkExternalFenceProperties::pname:exportFromImportedHandleTypes for
    pname:handleType
  * [[VUID-VkFenceGetWin32HandleInfoKHR-handleType-01451]]
    If pname:handleType refers to a handle type with copy payload
    transference semantics, pname:fence must: be signaled, or have an
    associated <<synchronization-fences-signaling,fence signal operation>>
    pending execution
  * [[VUID-VkFenceGetWin32HandleInfoKHR-handleType-01452]]
    pname:handleType must: be defined as an NT handle or a global share
    handle
****

include::{generated}/validity/structs/VkFenceGetWin32HandleInfoKHR.txt[]
--
endif::VK_KHR_external_fence_win32[]

ifdef::VK_KHR_external_fence_fd[]
[open,refpage='vkGetFenceFdKHR',desc='Get a POSIX file descriptor handle for a fence',type='protos']
--
To export a POSIX file descriptor representing the payload of a fence, call:

include::{generated}/api/protos/vkGetFenceFdKHR.txt[]

  * pname:device is the logical device that created the fence being
    exported.
  * pname:pGetFdInfo is a pointer to a slink:VkFenceGetFdInfoKHR structure
    containing parameters of the export operation.
  * pname:pFd will return the file descriptor representing the fence
    payload.

Each call to fname:vkGetFenceFdKHR must: create a new file descriptor and
transfer ownership of it to the application.
To avoid leaking resources, the application must: release ownership of the
file descriptor when it is no longer needed.

[NOTE]
.Note
====
Ownership can be released in many ways.
For example, the application can call code:close() on the file descriptor,
or transfer ownership back to Vulkan by using the file descriptor to import
a fence payload.
====

If pname:pGetFdInfo->handleType is
ename:VK_EXTERNAL_FENCE_HANDLE_TYPE_SYNC_FD_BIT and the fence is signaled at
the time fname:vkGetFenceFdKHR is called, pname:pFd may: return the value
`-1` instead of a valid file descriptor.

Where supported by the operating system, the implementation must: set the
file descriptor to be closed automatically when an code:execve system call
is made.

Exporting a file descriptor from a fence may: have side effects depending on
the transference of the specified handle type, as described in
<<synchronization-fences-importing,Importing Fence State>>.

include::{generated}/validity/protos/vkGetFenceFdKHR.txt[]
--

[open,refpage='VkFenceGetFdInfoKHR',desc='Structure describing a POSIX FD fence export operation',type='structs']
--
The sname:VkFenceGetFdInfoKHR structure is defined as:

include::{generated}/api/structs/VkFenceGetFdInfoKHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:fence is the fence from which state will be exported.
  * pname:handleType is a elink:VkExternalFenceHandleTypeFlagBits value
    specifying the type of handle requested.

The properties of the file descriptor returned depend on the value of
pname:handleType.
See elink:VkExternalFenceHandleTypeFlagBits for a description of the
properties of the defined external fence handle types.

.Valid Usage
****
  * [[VUID-VkFenceGetFdInfoKHR-handleType-01453]]
    pname:handleType must: have been included in
    slink:VkExportFenceCreateInfo::pname:handleTypes when pname:fence's
    current payload was created
  * [[VUID-VkFenceGetFdInfoKHR-handleType-01454]]
    If pname:handleType refers to a handle type with copy payload
    transference semantics, pname:fence must: be signaled, or have an
    associated <<synchronization-fences-signaling,fence signal operation>>
    pending execution
  * [[VUID-VkFenceGetFdInfoKHR-fence-01455]]
    pname:fence must: not currently have its payload replaced by an imported
    payload as described below in
    <<synchronization-fences-importing,Importing Fence Payloads>> unless
    that imported payload's handle type was included in
    slink:VkExternalFenceProperties::pname:exportFromImportedHandleTypes for
    pname:handleType
  * [[VUID-VkFenceGetFdInfoKHR-handleType-01456]]
    pname:handleType must: be defined as a POSIX file descriptor handle
****

include::{generated}/validity/structs/VkFenceGetFdInfoKHR.txt[]
--
endif::VK_KHR_external_fence_fd[]

[open,refpage='vkDestroyFence',desc='Destroy a fence object',type='protos']
--
To destroy a fence, call:

include::{generated}/api/protos/vkDestroyFence.txt[]

  * pname:device is the logical device that destroys the fence.
  * pname:fence is the handle of the fence to destroy.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.

.Valid Usage
****
  * [[VUID-vkDestroyFence-fence-01120]]
    All <<devsandqueues-submission, queue submission>> commands that refer
    to pname:fence must: have completed execution
  * [[VUID-vkDestroyFence-fence-01121]]
    If sname:VkAllocationCallbacks were provided when pname:fence was
    created, a compatible set of callbacks must: be provided here
  * [[VUID-vkDestroyFence-fence-01122]]
    If no sname:VkAllocationCallbacks were provided when pname:fence was
    created, pname:pAllocator must: be `NULL`
****

include::{generated}/validity/protos/vkDestroyFence.txt[]
--

[open,refpage='vkGetFenceStatus',desc='Return the status of a fence',type='protos']
--
To query the status of a fence from the host, call:

include::{generated}/api/protos/vkGetFenceStatus.txt[]

  * pname:device is the logical device that owns the fence.
  * pname:fence is the handle of the fence to query.

Upon success, fname:vkGetFenceStatus returns the status of the fence object,
with the following return codes:

.Fence Object Status Codes
[width="80%",options="header"]
|====
| Status | Meaning
| ename:VK_SUCCESS | The fence specified by pname:fence is signaled.
| ename:VK_NOT_READY | The fence specified by pname:fence is unsignaled.
| ename:VK_ERROR_DEVICE_LOST | The device has been lost.  See <<devsandqueues-lost-device,Lost Device>>.
|====

If a <<devsandqueues-submission, queue submission>> command is pending
execution, then the value returned by this command may: immediately be out
of date.

If the device has been lost (see <<devsandqueues-lost-device,Lost Device>>),
fname:vkGetFenceStatus may: return any of the above status codes.
If the device has been lost and fname:vkGetFenceStatus is called repeatedly,
it will eventually return either ename:VK_SUCCESS or
ename:VK_ERROR_DEVICE_LOST.

include::{generated}/validity/protos/vkGetFenceStatus.txt[]
--

[[synchronization-fences-unsignaling]]
[open,refpage='vkResetFences',desc='Resets one or more fence objects',type='protos']
--
To set the state of fences to unsignaled from the host, call:

include::{generated}/api/protos/vkResetFences.txt[]

  * pname:device is the logical device that owns the fences.
  * pname:fenceCount is the number of fences to reset.
  * pname:pFences is a pointer to an array of fence handles to reset.

ifdef::VK_VERSION_1_1,VK_KHR_external_fence[]

If any member of pname:pFences currently has its
<<synchronization-fences-importing, payload imported>> with temporary
permanence, that fence's prior permanent payload is first restored.
The remaining operations described therefore operate on the restored
payload.

endif::VK_VERSION_1_1,VK_KHR_external_fence[]

When flink:vkResetFences is executed on the host, it defines a _fence
unsignal operation_ for each fence, which resets the fence to the unsignaled
state.

If any member of pname:pFences is already in the unsignaled state when
flink:vkResetFences is executed, then flink:vkResetFences has no effect on
that fence.

.Valid Usage
****
  * [[VUID-vkResetFences-pFences-01123]]
    Each element of pname:pFences must: not be currently associated with any
    queue command that has not yet completed execution on that queue
****

include::{generated}/validity/protos/vkResetFences.txt[]
--

[[synchronization-fences-signaling]]
When a fence is submitted to a queue as part of a
<<devsandqueues-submission, queue submission>> command, it defines a memory
dependency on the batches that were submitted as part of that command, and
defines a _fence signal operation_ which sets the fence to the signaled
state.

The first <<synchronization-dependencies-scopes, synchronization scope>>
includes every batch submitted in the same <<devsandqueues-submission, queue
submission>> command.
Fence signal operations that are defined by flink:vkQueueSubmit additionally
include in the first synchronization scope all commands that occur earlier
in <<synchronization-submission-order,submission order>>.
Fence signal operations that are defined by flink:vkQueueSubmit or
flink:vkQueueBindSparse additionally include in the first synchronization
scope any semaphore and fence signal operations that occur earlier in
<<synchronization-signal-operation-order,signal operation order>>.

The second <<synchronization-dependencies-scopes, synchronization scope>>
only includes the fence signal operation.

The first <<synchronization-dependencies-access-scopes, access scope>>
includes all memory access performed by the device.

The second <<synchronization-dependencies-access-scopes, access scope>> is
empty.

[open,refpage='vkWaitForFences',desc='Wait for one or more fences to become signaled',type='protos']
--
To wait for one or more fences to enter the signaled state on the host,
call:

include::{generated}/api/protos/vkWaitForFences.txt[]

  * pname:device is the logical device that owns the fences.
  * pname:fenceCount is the number of fences to wait on.
  * pname:pFences is a pointer to an array of pname:fenceCount fence
    handles.
  * pname:waitAll is the condition that must: be satisfied to successfully
    unblock the wait.
    If pname:waitAll is ename:VK_TRUE, then the condition is that all fences
    in pname:pFences are signaled.
    Otherwise, the condition is that at least one fence in pname:pFences is
    signaled.
  * pname:timeout is the timeout period in units of nanoseconds.
    pname:timeout is adjusted to the closest value allowed by the
    implementation-dependent timeout accuracy, which may: be substantially
    longer than one nanosecond, and may: be longer than the requested
    period.

If the condition is satisfied when fname:vkWaitForFences is called, then
fname:vkWaitForFences returns immediately.
If the condition is not satisfied at the time fname:vkWaitForFences is
called, then fname:vkWaitForFences will block and wait until the condition
is satisfied or the pname:timeout has expired, whichever is sooner.

If pname:timeout is zero, then fname:vkWaitForFences does not wait, but
simply returns the current state of the fences.
ename:VK_TIMEOUT will be returned in this case if the condition is not
satisfied, even though no actual wait was performed.

If the condition is satisfied before the pname:timeout has expired,
fname:vkWaitForFences returns ename:VK_SUCCESS.
Otherwise, fname:vkWaitForFences returns ename:VK_TIMEOUT after the
pname:timeout has expired.

If device loss occurs (see <<devsandqueues-lost-device,Lost Device>>) before
the timeout has expired, fname:vkWaitForFences must: return in finite time
with either ename:VK_SUCCESS or ename:VK_ERROR_DEVICE_LOST.

[NOTE]
.Note
====
While we guarantee that fname:vkWaitForFences must: return in finite time,
no guarantees are made that it returns immediately upon device loss.
However, the client can reasonably expect that the delay will be on the
order of seconds and that calling fname:vkWaitForFences will not result in a
permanently (or seemingly permanently) dead process.
====

include::{generated}/validity/protos/vkWaitForFences.txt[]
--

[[synchronization-fences-waiting]]
An execution dependency is defined by waiting for a fence to become
signaled, either via flink:vkWaitForFences or by polling on
flink:vkGetFenceStatus.

The first <<synchronization-dependencies-scopes, synchronization scope>>
includes only the fence signal operation.

The second <<synchronization-dependencies-scopes, synchronization scope>>
includes the host operations of flink:vkWaitForFences or
flink:vkGetFenceStatus indicating that the fence has become signaled.

[NOTE]
.Note
====
Signaling a fence and waiting on the host does not guarantee that the
results of memory accesses will be visible to the host, as the access scope
of a memory dependency defined by a fence only includes device access.
A <<synchronization-memory-barriers, memory barrier>> or other memory
dependency must: be used to guarantee this.
See the description of <<synchronization-host-access-types, host access
types>> for more information.
====

ifdef::VK_EXT_display_control[]
include::{chapters}/VK_EXT_display_control/fence_events.txt[]
endif::VK_EXT_display_control[]


ifdef::VK_VERSION_1_1,VK_KHR_external_fence[]
[[synchronization-fences-importing]]
=== Importing Fence Payloads

Applications can: import a fence payload into an existing fence using an
external fence handle.
The effects of the import operation will be either temporary or permanent,
as specified by the application.
If the import is temporary, the fence will be _restored_ to its permanent
state the next time that fence is passed to flink:vkResetFences.

[NOTE]
.Note
====
Restoring a fence to its prior permanent payload is a distinct operation
from resetting a fence payload.
See flink:vkResetFences for more detail.
====

Performing a subsequent temporary import on a fence before resetting it has
no effect on this requirement; the next unsignal of the fence must: still
restore its last permanent state.
A permanent payload import behaves as if the target fence was destroyed, and
a new fence was created with the same handle but the imported payload.
Because importing a fence payload temporarily or permanently detaches the
existing payload from a fence, similar usage restrictions to those applied
to fname:vkDestroyFence are applied to any command that imports a fence
payload.
Which of these import types is used is referred to as the import operation's
_permanence_.
Each handle type supports either one or both types of permanence.

The implementation must: perform the import operation by either referencing
or copying the payload referred to by the specified external fence handle,
depending on the handle's type.
The import method used is referred to as the handle type's _transference_.
When using handle types with reference transference, importing a payload to
a fence adds the fence to the set of all fences sharing that payload.
This set includes the fence from which the payload was exported.
Fence signaling, waiting, and resetting operations performed on any fence in
the set must: behave as if the set were a single fence.
Importing a payload using handle types with copy transference creates a
duplicate copy of the payload at the time of import, but makes no further
reference to it.
Fence signaling, waiting, and resetting operations performed on the target
of copy imports must: not affect any other fence or payload.

Export operations have the same transference as the specified handle type's
import operations.
Additionally, exporting a fence payload to a handle with copy transference
has the same side effects on the source fence's payload as executing a fence
reset operation.
If the fence was using a temporarily imported payload, the fence's prior
permanent payload will be restored.

ifdef::VK_KHR_external_fence_win32,VK_KHR_external_fence_fd[]
[NOTE]
.Note
====
The
ifdef::VK_KHR_external_fence_win32+VK_KHR_external_fence_fd[tables]
ifndef::VK_KHR_external_fence_win32+VK_KHR_external_fence_fd[table]
ifdef::VK_KHR_external_fence_win32[]
<<synchronization-fence-handletypes-win32,Handle Types Supported by
sname:VkImportFenceWin32HandleInfoKHR>>
endif::VK_KHR_external_fence_win32[]
ifdef::VK_KHR_external_fence_win32+VK_KHR_external_fence_fd[and]
ifdef::VK_KHR_external_fence_fd[]
<<synchronization-fence-handletypes-fd,Handle Types Supported by
sname:VkImportFenceFdInfoKHR>>
endif::VK_KHR_external_fence_fd[]
ifdef::VK_KHR_external_fence_win32+VK_KHR_external_fence_fd[define]
ifndef::VK_KHR_external_fence_win32+VK_KHR_external_fence_fd[defines]
the permanence and transference of each handle type.
====
endif::VK_KHR_external_fence_win32,VK_KHR_external_fence_fd[]

<<fundamentals-threadingbehavior,External synchronization>> allows
implementations to modify an object's internal state, i.e. payload, without
internal synchronization.
However, for fences sharing a payload across processes, satisfying the
external synchronization requirements of sname:VkFence parameters as if all
fences in the set were the same object is sometimes infeasible.
Satisfying valid usage constraints on the state of a fence would similarly
require impractical coordination or levels of trust between processes.
Therefore, these constraints only apply to a specific fence handle, not to
its payload.
For distinct fence objects which share a payload:

  * If multiple commands which queue a signal operation, or which unsignal a
    fence, are called concurrently, behavior will be as if the commands were
    called in an arbitrary sequential order.
  * If a queue submission command is called with a fence that is sharing a
    payload, and the payload is already associated with another queue
    command that has not yet completed execution, either one or both of the
    commands will cause the fence to become signaled when they complete
    execution.
  * If a fence payload is reset while it is associated with a queue command
    that has not yet completed execution, the payload will become
    unsignaled, but may: become signaled again when the command completes
    execution.
  * In the preceding cases, any of the devices associated with the fences
    sharing the payload may: be lost, or any of the queue submission or
    fence reset commands may: return ename:VK_ERROR_INITIALIZATION_FAILED.

Other than these non-deterministic results, behavior is well defined.
In particular:

  * The implementation must: not crash or enter an internally inconsistent
    state where future valid Vulkan commands might cause undefined: results,
  * Timeouts on future wait commands on fences sharing the payload must: be
    effective.

[NOTE]
.Note
====
These rules allow processes to synchronize access to shared memory without
trusting each other.
However, such processes must still be cautious not to use the shared fence
for more than synchronizing access to the shared memory.
For example, a process should not use a fence with shared payload to tell
when commands it submitted to a queue have completed and objects used by
those commands may be destroyed, since the other process can accidentally or
maliciously cause the fence to signal before the commands actually complete.
====

When a fence is using an imported payload, its
slink:VkExportFenceCreateInfo::pname:handleTypes value is specified when
creating the fence from which the payload was exported, rather than
specified when creating the fence.
Additionally,
slink:VkExternalFenceProperties::pname:exportFromImportedHandleTypes
restricts which handle types can: be exported from such a fence based on the
specific handle type used to import the current payload.
ifdef::VK_KHR_swapchain[]
Passing a fence to flink:vkAcquireNextImageKHR is equivalent to temporarily
importing a fence payload to that fence.

[NOTE]
.Note
====
Because the exportable handle types of an imported fence correspond to its
current imported payload, and flink:vkAcquireNextImageKHR behaves the same
as a temporary import operation for which the source fence is opaque to the
application, applications have no way of determining whether any external
handle types can: be exported from a fence in this state.
Therefore, applications must: not attempt to export handles from fences
using a temporarily imported payload from flink:vkAcquireNextImageKHR.
====
endif::VK_KHR_swapchain[]

When importing a fence payload, it is the responsibility of the application
to ensure the external handles meet all valid usage requirements.
However, implementations must: perform sufficient validation of external
handles to ensure that the operation results in a valid fence which will not
cause program termination, device loss, queue stalls, host thread stalls, or
corruption of other resources when used as allowed according to its import
parameters.
If the external handle provided does not meet these requirements, the
implementation must: fail the fence payload import operation with the error
code ename:VK_ERROR_INVALID_EXTERNAL_HANDLE.
endif::VK_VERSION_1_1,VK_KHR_external_fence[]

ifdef::VK_KHR_external_fence_win32[]
[open,refpage='vkImportFenceWin32HandleKHR',desc='Import a fence from a Windows HANDLE',type='protos']
--
To import a fence payload from a Windows handle, call:

include::{generated}/api/protos/vkImportFenceWin32HandleKHR.txt[]

  * pname:device is the logical device that created the fence.
  * pname:pImportFenceWin32HandleInfo is a pointer to a
    slink:VkImportFenceWin32HandleInfoKHR structure specifying the fence and
    import parameters.

Importing a fence payload from Windows handles does not transfer ownership
of the handle to the Vulkan implementation.
For handle types defined as NT handles, the application must: release
ownership using the code:CloseHandle system call when the handle is no
longer needed.

Applications can: import the same fence payload into multiple instances of
Vulkan, into the same instance from which it was exported, and multiple
times into a given Vulkan instance.

.Valid Usage
****
  * [[VUID-vkImportFenceWin32HandleKHR-fence-04448]]
    pname:fence must: not be associated with any queue command that has not
    yet completed execution on that queue
****

include::{generated}/validity/protos/vkImportFenceWin32HandleKHR.txt[]
--

[open,refpage='VkImportFenceWin32HandleInfoKHR',desc='(None)',type='structs']
--
The sname:VkImportFenceWin32HandleInfoKHR structure is defined as:

include::{generated}/api/structs/VkImportFenceWin32HandleInfoKHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:fence is the fence into which the state will be imported.
  * pname:flags is a bitmask of elink:VkFenceImportFlagBits specifying
    additional parameters for the fence payload import operation.
  * pname:handleType is a elink:VkExternalFenceHandleTypeFlagBits value
    specifying the type of pname:handle.
  * pname:handle is `NULL` or the external handle to import.
  * pname:name is `NULL` or a null-terminated UTF-16 string naming the
    underlying synchronization primitive to import.

The handle types supported by pname:handleType are:

[[synchronization-fence-handletypes-win32]]
.Handle Types Supported by sname:VkImportFenceWin32HandleInfoKHR
[width="80%",options="header"]
|====
| Handle Type                                                  | Transference | Permanence Supported
| ename:VK_EXTERNAL_FENCE_HANDLE_TYPE_OPAQUE_WIN32_BIT     | Reference    | Temporary,Permanent
| ename:VK_EXTERNAL_FENCE_HANDLE_TYPE_OPAQUE_WIN32_KMT_BIT | Reference    | Temporary,Permanent
|====

.Valid Usage
****
  * [[VUID-VkImportFenceWin32HandleInfoKHR-handleType-01457]]
    pname:handleType must: be a value included in the
    <<synchronization-fence-handletypes-win32, Handle Types Supported by
    sname:VkImportFenceWin32HandleInfoKHR>> table
  * [[VUID-VkImportFenceWin32HandleInfoKHR-handleType-01459]]
    If pname:handleType is not
    ename:VK_EXTERNAL_FENCE_HANDLE_TYPE_OPAQUE_WIN32_BIT, pname:name must:
    be `NULL`
  * [[VUID-VkImportFenceWin32HandleInfoKHR-handleType-01460]]
    If pname:handle is `NULL`, pname:name must: name a valid synchronization
    primitive of the type specified by pname:handleType
  * [[VUID-VkImportFenceWin32HandleInfoKHR-handleType-01461]]
    If pname:name is `NULL`, pname:handle must: be a valid handle of the
    type specified by pname:handleType
  * [[VUID-VkImportFenceWin32HandleInfoKHR-handle-01462]]
    If pname:handle is not `NULL`, pname:name must: be `NULL`
  * [[VUID-VkImportFenceWin32HandleInfoKHR-handle-01539]]
    If pname:handle is not `NULL`, it must: obey any requirements listed for
    pname:handleType in <<external-fence-handle-types-compatibility,external
    fence handle types compatibility>>
  * [[VUID-VkImportFenceWin32HandleInfoKHR-name-01540]]
    If pname:name is not `NULL`, it must: obey any requirements listed for
    pname:handleType in <<external-fence-handle-types-compatibility,external
    fence handle types compatibility>>
****

include::{generated}/validity/structs/VkImportFenceWin32HandleInfoKHR.txt[]
--
endif::VK_KHR_external_fence_win32[]

ifdef::VK_KHR_external_fence_fd[]
[open,refpage='vkImportFenceFdKHR',desc='Import a fence from a POSIX file descriptor',type='protos']
--
To import a fence payload from a POSIX file descriptor, call:

include::{generated}/api/protos/vkImportFenceFdKHR.txt[]

  * pname:device is the logical device that created the fence.
  * pname:pImportFenceFdInfo is a pointer to a slink:VkImportFenceFdInfoKHR
    structure specifying the fence and import parameters.

Importing a fence payload from a file descriptor transfers ownership of the
file descriptor from the application to the Vulkan implementation.
The application must: not perform any operations on the file descriptor
after a successful import.

Applications can: import the same fence payload into multiple instances of
Vulkan, into the same instance from which it was exported, and multiple
times into a given Vulkan instance.

.Valid Usage
****
  * [[VUID-vkImportFenceFdKHR-fence-01463]]
    pname:fence must: not be associated with any queue command that has not
    yet completed execution on that queue
****

include::{generated}/validity/protos/vkImportFenceFdKHR.txt[]
--

[open,refpage='VkImportFenceFdInfoKHR',desc='(None)',type='structs']
--
The sname:VkImportFenceFdInfoKHR structure is defined as:

include::{generated}/api/structs/VkImportFenceFdInfoKHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:fence is the fence into which the payload will be imported.
  * pname:flags is a bitmask of elink:VkFenceImportFlagBits specifying
    additional parameters for the fence payload import operation.
  * pname:handleType is a elink:VkExternalFenceHandleTypeFlagBits value
    specifying the type of pname:fd.
  * pname:fd is the external handle to import.

The handle types supported by pname:handleType are:

[[synchronization-fence-handletypes-fd]]
.Handle Types Supported by sname:VkImportFenceFdInfoKHR
[width="80%",options="header"]
|====
| Handle Type                                           | Transference | Permanence Supported
| ename:VK_EXTERNAL_FENCE_HANDLE_TYPE_OPAQUE_FD_BIT | Reference    | Temporary,Permanent
| ename:VK_EXTERNAL_FENCE_HANDLE_TYPE_SYNC_FD_BIT   | Copy         | Temporary
|====

.Valid Usage
****
  * [[VUID-VkImportFenceFdInfoKHR-handleType-01464]]
    pname:handleType must: be a value included in the
    <<synchronization-fence-handletypes-fd, Handle Types Supported by
    sname:VkImportFenceFdInfoKHR>> table
  * [[VUID-VkImportFenceFdInfoKHR-fd-01541]]
    pname:fd must: obey any requirements listed for pname:handleType in
    <<external-fence-handle-types-compatibility,external fence handle types
    compatibility>>
****

If pname:handleType is ename:VK_EXTERNAL_FENCE_HANDLE_TYPE_SYNC_FD_BIT, the
special value `-1` for pname:fd is treated like a valid sync file descriptor
referring to an object that has already signaled.
The import operation will succeed and the sname:VkFence will have a
temporarily imported payload as if a valid file descriptor had been
provided.

[NOTE]
.Note
====
This special behavior for importing an invalid sync file descriptor allows
easier interoperability with other system APIs which use the convention that
an invalid sync file descriptor represents work that has already completed
and does not need to be waited for.
It is consistent with the option for implementations to return a `-1` file
descriptor when exporting a ename:VK_EXTERNAL_FENCE_HANDLE_TYPE_SYNC_FD_BIT
from a sname:VkFence which is signaled.
====

include::{generated}/validity/structs/VkImportFenceFdInfoKHR.txt[]
--
endif::VK_KHR_external_fence_fd[]

ifdef::VK_VERSION_1_1,VK_KHR_external_fence[]
ifdef::VK_KHR_external_fence_win32,VK_KHR_external_fence_fd[]
[open,refpage='VkFenceImportFlagBits',desc='Bitmask specifying additional parameters of fence payload import',type='enums']
--
Bits which can: be set in

ifdef::VK_KHR_external_fence_win32[]
  * slink:VkImportFenceWin32HandleInfoKHR::pname:flags
endif::VK_KHR_external_fence_win32[]
ifdef::VK_KHR_external_fence_fd[]
  * slink:VkImportFenceFdInfoKHR::pname:flags
endif::VK_KHR_external_fence_fd[]

specifying additional parameters of a fence import operation are:

include::{generated}/api/enums/VkFenceImportFlagBits.txt[]

ifdef::VK_KHR_external_fence[]
or the equivalent

include::{generated}/api/enums/VkFenceImportFlagBitsKHR.txt[]
endif::VK_KHR_external_fence[]

  * ename:VK_FENCE_IMPORT_TEMPORARY_BIT specifies that the fence payload
    will be imported only temporarily, as described in
    <<synchronization-fences-importing,Importing Fence Payloads>>,
    regardless of the permanence of pname:handleType.
--

[open,refpage='VkFenceImportFlags',desc='Bitmask of VkFenceImportFlagBits',type='flags']
--
include::{generated}/api/flags/VkFenceImportFlags.txt[]

ifdef::VK_KHR_external_fence[]
or the equivalent

include::{generated}/api/flags/VkFenceImportFlagsKHR.txt[]
endif::VK_KHR_external_fence[]

tname:VkFenceImportFlags is a bitmask type for setting a mask of zero or
more elink:VkFenceImportFlagBits.
--
endif::VK_KHR_external_fence_win32,VK_KHR_external_fence_fd[]
endif::VK_VERSION_1_1,VK_KHR_external_fence[]


[[synchronization-semaphores]]
== Semaphores

[open,refpage='VkSemaphore',desc='Opaque handle to a semaphore object',type='handles']
--
Semaphores are a synchronization primitive that can: be used to insert a
dependency
ifndef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
between queue operations.
Semaphores have two states - signaled and unsignaled.
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
between queue operations or between a queue operation and the host.
<<glossary, Binary semaphores>> have two states - signaled and unsignaled.
<<glossary, Timeline semaphores>> have a strictly increasing 64-bit unsigned
integer payload and are signaled with respect to a particular reference
value.
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
A semaphore can: be signaled after execution of a queue operation is
completed, and a queue operation can: wait for a semaphore to become
signaled before it begins execution.
ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
A timeline semaphore can: additionally be signaled from the host with the
flink:vkSignalSemaphore command and waited on from the host with the
flink:vkWaitSemaphores command.
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]

ifdef::VK_VERSION_1_1,VK_KHR_external_semaphore[]
[[synchronization-semaphores-payloads]]
The internal data of a semaphore may: include a reference to any resources
and pending work associated with signal or unsignal operations performed on
that semaphore object, collectively referred to as the semaphore's
_payload_.
Mechanisms to import and export that internal data to and from semaphores
are provided <<VkExportSemaphoreCreateInfo, below>>.
These mechanisms indirectly enable applications to share semaphore state
between two or more semaphores and other synchronization primitives across
process and API boundaries.

endif::VK_VERSION_1_1,VK_KHR_external_semaphore[]

Semaphores are represented by sname:VkSemaphore handles:

include::{generated}/api/handles/VkSemaphore.txt[]
--

[open,refpage='vkCreateSemaphore',desc='Create a new queue semaphore object',type='protos']
--
To create a semaphore, call:

include::{generated}/api/protos/vkCreateSemaphore.txt[]

  * pname:device is the logical device that creates the semaphore.
  * pname:pCreateInfo is a pointer to a slink:VkSemaphoreCreateInfo
    structure containing information about how the semaphore is to be
    created.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.
  * pname:pSemaphore is a pointer to a handle in which the resulting
    semaphore object is returned.

ifndef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
This command creates a _binary semaphore_ that has a boolean payload
indicating whether the semaphore is currently signaled or unsignaled.
When created, the semaphore is in the unsignaled state.
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]

include::{generated}/validity/protos/vkCreateSemaphore.txt[]
--

[open,refpage='VkSemaphoreCreateInfo',desc='Structure specifying parameters of a newly created semaphore',type='structs']
--
The sname:VkSemaphoreCreateInfo structure is defined as:

include::{generated}/api/structs/VkSemaphoreCreateInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:flags is reserved for future use.

include::{generated}/validity/structs/VkSemaphoreCreateInfo.txt[]
--

[open,refpage='VkSemaphoreCreateFlags',desc='Reserved for future use',type='flags']
--
include::{generated}/api/flags/VkSemaphoreCreateFlags.txt[]

tname:VkSemaphoreCreateFlags is a bitmask type for setting a mask, but is
currently reserved for future use.
--

ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
[open,refpage='VkSemaphoreTypeCreateInfo',desc='Structure specifying the type of a newly created semaphore',type='structs',alias='VkSemaphoreTypeCreateInfoKHR']
--
The sname:VkSemaphoreTypeCreateInfo structure is defined as:

include::{generated}/api/structs/VkSemaphoreTypeCreateInfo.txt[]

ifdef::VK_KHR_timeline_semaphore[]
or the equivalent

include::{generated}/api/structs/VkSemaphoreTypeCreateInfoKHR.txt[]
endif::VK_KHR_timeline_semaphore[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:semaphoreType is a elink:VkSemaphoreType value specifying the type
    of the semaphore.
  * pname:initialValue is the initial payload value if pname:semaphoreType
    is ename:VK_SEMAPHORE_TYPE_TIMELINE.

To create a semaphore of a specific type, add a
sname:VkSemaphoreTypeCreateInfo structure to the
slink:VkSemaphoreCreateInfo::pname:pNext chain.

If no sname:VkSemaphoreTypeCreateInfo structure is included in the
pname:pNext chain of slink:VkSemaphoreCreateInfo, then the created semaphore
will have a default elink:VkSemaphoreType of ename:VK_SEMAPHORE_TYPE_BINARY.

.Valid Usage
****
  * [[VUID-VkSemaphoreTypeCreateInfo-timelineSemaphore-03252]]
    If the <<features-timelineSemaphore,pname:timelineSemaphore>> feature is
    not enabled, pname:semaphoreType must: not equal
    ename:VK_SEMAPHORE_TYPE_TIMELINE
  * [[VUID-VkSemaphoreTypeCreateInfo-semaphoreType-03279]]
    If pname:semaphoreType is ename:VK_SEMAPHORE_TYPE_BINARY,
    pname:initialValue must: be zero
****

include::{generated}/validity/structs/VkSemaphoreTypeCreateInfo.txt[]
--

[open,refpage='VkSemaphoreType',desc='Sepcifies the type of a semaphore object',type='enums',alias='VkSemaphoreTypeKHR']
--
Possible values of slink:VkSemaphoreTypeCreateInfo::pname:semaphoreType,
specifying the type of a semaphore, are:

include::{generated}/api/enums/VkSemaphoreType.txt[]

ifdef::VK_KHR_timeline_semaphore[]
or the equivalent

include::{generated}/api/enums/VkSemaphoreTypeKHR.txt[]
endif::VK_KHR_timeline_semaphore[]

  * ename:VK_SEMAPHORE_TYPE_BINARY specifies a _binary semaphore_ type that
    has a boolean payload indicating whether the semaphore is currently
    signaled or unsignaled.
    When created, the semaphore is in the unsignaled state.
  * ename:VK_SEMAPHORE_TYPE_TIMELINE specifies a _timeline semaphore_ type
    that has a strictly increasing 64-bit unsigned integer payload
    indicating whether the semaphore is signaled with respect to a
    particular reference value.
    When created, the semaphore payload has the value given by the
    pname:initialValue field of slink:VkSemaphoreTypeCreateInfo.
--
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]

ifdef::VK_VERSION_1_1,VK_KHR_external_semaphore[]
[open,refpage='VkExportSemaphoreCreateInfo',desc='Structure specifying handle types that can be exported from a semaphore',type='structs']
--
To create a semaphore whose payload can: be exported to external handles,
add a slink:VkExportSemaphoreCreateInfo structure to the pname:pNext chain
of the slink:VkSemaphoreCreateInfo structure.
The sname:VkExportSemaphoreCreateInfo structure is defined as:

include::{generated}/api/structs/VkExportSemaphoreCreateInfo.txt[]

ifdef::VK_KHR_external_semaphore[]
or the equivalent

include::{generated}/api/structs/VkExportSemaphoreCreateInfoKHR.txt[]
endif::VK_KHR_external_semaphore[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:handleTypes is a bitmask of
    elink:VkExternalSemaphoreHandleTypeFlagBits specifying one or more
    semaphore handle types the application can: export from the resulting
    semaphore.
    The application can: request multiple handle types for the same
    semaphore.

.Valid Usage
****
  * [[VUID-VkExportSemaphoreCreateInfo-handleTypes-01124]]
    The bits in pname:handleTypes must: be supported and compatible, as
    reported by slink:VkExternalSemaphoreProperties
****

include::{generated}/validity/structs/VkExportSemaphoreCreateInfo.txt[]
--
endif::VK_VERSION_1_1,VK_KHR_external_semaphore[]

ifdef::VK_KHR_external_semaphore_win32[]
[open,refpage='VkExportSemaphoreWin32HandleInfoKHR',desc='Structure specifying additional attributes of Windows handles exported from a semaphore',type='structs']
--
To specify additional attributes of NT handles exported from a semaphore,
add a sname:VkExportSemaphoreWin32HandleInfoKHR structure to the pname:pNext
chain of the slink:VkSemaphoreCreateInfo structure.
The sname:VkExportSemaphoreWin32HandleInfoKHR structure is defined as:

include::{generated}/api/structs/VkExportSemaphoreWin32HandleInfoKHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:pAttributes is a pointer to a Windows code:SECURITY_ATTRIBUTES
    structure specifying security attributes of the handle.
  * pname:dwAccess is a code:DWORD specifying access rights of the handle.
  * pname:name is a null-terminated UTF-16 string to associate with the
    underlying synchronization primitive referenced by NT handles exported
    from the created semaphore.

If slink:VkExportSemaphoreCreateInfo is not included in the same pname:pNext
chain, this structure is ignored.

If slink:VkExportSemaphoreCreateInfo is included in the pname:pNext chain of
slink:VkSemaphoreCreateInfo with a Windows pname:handleType, but either
sname:VkExportSemaphoreWin32HandleInfoKHR is not included in the pname:pNext
chain, or if it is but pname:pAttributes is set to `NULL`, default security
descriptor values will be used, and child processes created by the
application will not inherit the handle, as described in the MSDN
documentation for "`Synchronization Object Security and Access Rights`"^1^.
Further, if the structure is not present, the access rights used depend on
the handle type.

For handles of the following types:

ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_OPAQUE_WIN32_BIT

The implementation must: ensure the access rights allow both signal and wait
operations on the semaphore.

For handles of the following types:

ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_D3D12_FENCE_BIT

The access rights must: be:

code:GENERIC_ALL

1::
    https://docs.microsoft.com/en-us/windows/win32/sync/synchronization-object-security-and-access-rights

.Valid Usage
****
  * [[VUID-VkExportSemaphoreWin32HandleInfoKHR-handleTypes-01125]]
    If slink:VkExportSemaphoreCreateInfo::pname:handleTypes does not include
    ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_OPAQUE_WIN32_BIT or
    ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_D3D12_FENCE_BIT,
    sname:VkExportSemaphoreWin32HandleInfoKHR must: not be included in the
    pname:pNext chain of slink:VkSemaphoreCreateInfo
****

include::{generated}/validity/structs/VkExportSemaphoreWin32HandleInfoKHR.txt[]
--

[open,refpage='vkGetSemaphoreWin32HandleKHR',desc='Get a Windows HANDLE for a semaphore',type='protos']
--
To export a Windows handle representing the payload of a semaphore, call:

include::{generated}/api/protos/vkGetSemaphoreWin32HandleKHR.txt[]

  * pname:device is the logical device that created the semaphore being
    exported.
  * pname:pGetWin32HandleInfo is a pointer to a
    slink:VkSemaphoreGetWin32HandleInfoKHR structure containing parameters
    of the export operation.
  * pname:pHandle will return the Windows handle representing the semaphore
    state.

For handle types defined as NT handles, the handles returned by
fname:vkGetSemaphoreWin32HandleKHR are owned by the application.
To avoid leaking resources, the application must: release ownership of them
using the code:CloseHandle system call when they are no longer needed.

Exporting a Windows handle from a semaphore may: have side effects depending
on the transference of the specified handle type, as described in
<<synchronization-semaphores-importing,Importing Semaphore Payloads>>.

include::{generated}/validity/protos/vkGetSemaphoreWin32HandleKHR.txt[]
--

[open,refpage='VkSemaphoreGetWin32HandleInfoKHR',desc='Structure describing a Win32 handle semaphore export operation',type='structs']
--
The sname:VkSemaphoreGetWin32HandleInfoKHR structure is defined as:

include::{generated}/api/structs/VkSemaphoreGetWin32HandleInfoKHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:semaphore is the semaphore from which state will be exported.
  * pname:handleType is a elink:VkExternalSemaphoreHandleTypeFlagBits value
    specifying the type of handle requested.

The properties of the handle returned depend on the value of
pname:handleType.
See elink:VkExternalSemaphoreHandleTypeFlagBits for a description of the
properties of the defined external semaphore handle types.

.Valid Usage
****
  * [[VUID-VkSemaphoreGetWin32HandleInfoKHR-handleType-01126]]
    pname:handleType must: have been included in
    slink:VkExportSemaphoreCreateInfo::pname:handleTypes when the
    pname:semaphore's current payload was created
  * [[VUID-VkSemaphoreGetWin32HandleInfoKHR-handleType-01127]]
    If pname:handleType is defined as an NT handle,
    flink:vkGetSemaphoreWin32HandleKHR must: be called no more than once for
    each valid unique combination of pname:semaphore and pname:handleType
  * [[VUID-VkSemaphoreGetWin32HandleInfoKHR-semaphore-01128]]
    pname:semaphore must: not currently have its payload replaced by an
    imported payload as described below in
    <<synchronization-semaphores-importing,Importing Semaphore Payloads>>
    unless that imported payload's handle type was included in
    slink:VkExternalSemaphoreProperties::pname:exportFromImportedHandleTypes
    for pname:handleType
  * [[VUID-VkSemaphoreGetWin32HandleInfoKHR-handleType-01129]]
    If pname:handleType refers to a handle type with copy payload
    transference semantics, as defined below in
    <<synchronization-semaphores-importing,Importing Semaphore Payloads>>,
    there must: be no queue waiting on pname:semaphore
  * [[VUID-VkSemaphoreGetWin32HandleInfoKHR-handleType-01130]]
    If pname:handleType refers to a handle type with copy payload
    transference semantics, pname:semaphore must: be signaled, or have an
    associated <<synchronization-semaphores-signaling,semaphore signal
    operation>> pending execution
  * [[VUID-VkSemaphoreGetWin32HandleInfoKHR-handleType-01131]]
    pname:handleType must: be defined as an NT handle or a global share
    handle
****

include::{generated}/validity/structs/VkSemaphoreGetWin32HandleInfoKHR.txt[]
--
endif::VK_KHR_external_semaphore_win32[]

ifdef::VK_KHR_external_semaphore_fd[]
[open,refpage='vkGetSemaphoreFdKHR',desc='Get a POSIX file descriptor handle for a semaphore',type='protos']
--
To export a POSIX file descriptor representing the payload of a semaphore,
call:

include::{generated}/api/protos/vkGetSemaphoreFdKHR.txt[]

  * pname:device is the logical device that created the semaphore being
    exported.
  * pname:pGetFdInfo is a pointer to a slink:VkSemaphoreGetFdInfoKHR
    structure containing parameters of the export operation.
  * pname:pFd will return the file descriptor representing the semaphore
    payload.

Each call to fname:vkGetSemaphoreFdKHR must: create a new file descriptor
and transfer ownership of it to the application.
To avoid leaking resources, the application must: release ownership of the
file descriptor when it is no longer needed.

[NOTE]
.Note
====
Ownership can be released in many ways.
For example, the application can call code:close() on the file descriptor,
or transfer ownership back to Vulkan by using the file descriptor to import
a semaphore payload.
====
Where supported by the operating system, the implementation must: set the
file descriptor to be closed automatically when an code:execve system call
is made.

Exporting a file descriptor from a semaphore may: have side effects
depending on the transference of the specified handle type, as described in
<<synchronization-semaphores-importing,Importing Semaphore State>>.

include::{generated}/validity/protos/vkGetSemaphoreFdKHR.txt[]
--

[open,refpage='VkSemaphoreGetFdInfoKHR',desc='Structure describing a POSIX FD semaphore export operation',type='structs']
--
The sname:VkSemaphoreGetFdInfoKHR structure is defined as:

include::{generated}/api/structs/VkSemaphoreGetFdInfoKHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:semaphore is the semaphore from which state will be exported.
  * pname:handleType is a elink:VkExternalSemaphoreHandleTypeFlagBits value
    specifying the type of handle requested.

The properties of the file descriptor returned depend on the value of
pname:handleType.
See elink:VkExternalSemaphoreHandleTypeFlagBits for a description of the
properties of the defined external semaphore handle types.

.Valid Usage
****
  * [[VUID-VkSemaphoreGetFdInfoKHR-handleType-01132]]
    pname:handleType must: have been included in
    slink:VkExportSemaphoreCreateInfo::pname:handleTypes when
    pname:semaphore's current payload was created
  * [[VUID-VkSemaphoreGetFdInfoKHR-semaphore-01133]]
    pname:semaphore must: not currently have its payload replaced by an
    imported payload as described below in
    <<synchronization-semaphores-importing,Importing Semaphore Payloads>>
    unless that imported payload's handle type was included in
    slink:VkExternalSemaphoreProperties::pname:exportFromImportedHandleTypes
    for pname:handleType
  * [[VUID-VkSemaphoreGetFdInfoKHR-handleType-01134]]
    If pname:handleType refers to a handle type with copy payload
    transference semantics, as defined below in
    <<synchronization-semaphores-importing,Importing Semaphore Payloads>>,
    there must: be no queue waiting on pname:semaphore
  * [[VUID-VkSemaphoreGetFdInfoKHR-handleType-01135]]
    If pname:handleType refers to a handle type with copy payload
    transference semantics, pname:semaphore must: be signaled, or have an
    associated <<synchronization-semaphores-signaling,semaphore signal
    operation>> pending execution
  * [[VUID-VkSemaphoreGetFdInfoKHR-handleType-01136]]
    pname:handleType must: be defined as a POSIX file descriptor handle
ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
  * [[VUID-VkSemaphoreGetFdInfoKHR-handleType-03253]]
    If pname:handleType refers to a handle type with copy payload
    transference semantics, pname:semaphore must: have been created with a
    elink:VkSemaphoreType of ename:VK_SEMAPHORE_TYPE_BINARY
  * [[VUID-VkSemaphoreGetFdInfoKHR-handleType-03254]]
    If pname:handleType refers to a handle type with copy payload
    transference semantics, pname:semaphore must: have an associated
    semaphore signal operation that has been submitted for execution and any
    semaphore signal operations on which it depends (if any) must: have also
    been submitted for execution
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
****

include::{generated}/validity/structs/VkSemaphoreGetFdInfoKHR.txt[]
--
endif::VK_KHR_external_semaphore_fd[]

ifdef::VK_FUCHSIA_external_semaphore[]
[open,refpage='vkGetSemaphoreZirconHandleFUCHSIA',desc='Get a Zircon event handle for a semaphore',type='protos']
--
To export a Zircon event handle representing the payload of a semaphore,
call:

include::{generated}/api/protos/vkGetSemaphoreZirconHandleFUCHSIA.txt[]

  * pname:device is the logical device that created the semaphore being
    exported.
  * pname:pGetZirconHandleInfo is a pointer to a
    slink:VkSemaphoreGetZirconHandleInfoFUCHSIA structure containing
    parameters of the export operation.
  * pname:pZirconHandle will return the Zircon event handle representing the
    semaphore payload.

Each call to fname:vkGetSemaphoreZirconHandleFUCHSIA must: create a Zircon
event handle and transfer ownership of it to the application.
To avoid leaking resources, the application must: release ownership of the
Zircon event handle when it is no longer needed.

[NOTE]
.Note
====
Ownership can be released in many ways.
For example, the application can call zx_handle_close() on the file
descriptor, or transfer ownership back to Vulkan by using the file
descriptor to import a semaphore payload.
====

Exporting a Zircon event handle from a semaphore may: have side effects
depending on the transference of the specified handle type, as described in
<<synchronization-semaphores-importing,Importing Semaphore State>>.

include::{generated}/validity/protos/vkGetSemaphoreZirconHandleFUCHSIA.txt[]
--

[open,refpage='VkSemaphoreGetZirconHandleInfoFUCHSIA',desc='Structure describing a Zircon event handle semaphore export operation',type='structs']
--
The sname:VkSemaphoreGetZirconHandleInfoFUCHSIA structure is defined as:

include::{generated}/api/structs/VkSemaphoreGetZirconHandleInfoFUCHSIA.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:semaphore is the semaphore from which state will be exported.
  * pname:handleType is a elink:VkExternalSemaphoreHandleTypeFlagBits value
    specifying the type of handle requested.

The properties of the Zircon event handle returned depend on the value of
pname:handleType.
See elink:VkExternalSemaphoreHandleTypeFlagBits for a description of the
properties of the defined external semaphore handle types.

.Valid Usage
****
  * [[VUID-VkSemaphoreGetZirconHandleInfoFUCHSIA-handleType-04758]]
    pname:handleType must: have been included in
    slink:VkExportSemaphoreCreateInfo::pname:handleTypes when
    pname:semaphore's current payload was created
  * [[VUID-VkSemaphoreGetZirconHandleInfoFUCHSIA-semaphore-04759]]
    pname:semaphore must: not currently have its payload replaced by an
    imported payload as described below in
    <<synchronization-semaphores-importing,Importing Semaphore Payloads>>
    unless that imported payload's handle type was included in
    slink:VkExternalSemaphoreProperties::pname:exportFromImportedHandleTypes
    for pname:handleType
  * [[VUID-VkSemaphoreGetZirconHandleInfoFUCHSIA-handleType-04760]]
    If pname:handleType refers to a handle type with copy payload
    transference semantics, as defined below in
    <<synchronization-semaphores-importing,Importing Semaphore Payloads>>,
    there must: be no queue waiting on pname:semaphore
  * [[VUID-VkSemaphoreGetZirconHandleInfoFUCHSIA-handleType-04761]]
    If pname:handleType refers to a handle type with copy payload
    transference semantics, pname:semaphore must: be signaled, or have an
    associated <<synchronization-semaphores-signaling,semaphore signal
    operation>> pending execution
  * [[VUID-VkSemaphoreGetZirconHandleInfoFUCHSIA-handleType-04762]]
    pname:handleType must: be defined as a Zircon event handle
  * [[VUID-VkSemaphoreGetZirconHandleInfoFUCHSIA-semaphore-04763]]
    pname:semaphore must: have been created with a elink:VkSemaphoreType of
    ename:VK_SEMAPHORE_TYPE_BINARY
****

include::{generated}/validity/structs/VkSemaphoreGetZirconHandleInfoFUCHSIA.txt[]
--
endif::VK_FUCHSIA_external_semaphore[]

[open,refpage='vkDestroySemaphore',desc='Destroy a semaphore object',type='protos']
--
To destroy a semaphore, call:

include::{generated}/api/protos/vkDestroySemaphore.txt[]

  * pname:device is the logical device that destroys the semaphore.
  * pname:semaphore is the handle of the semaphore to destroy.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.

.Valid Usage
****
  * [[VUID-vkDestroySemaphore-semaphore-01137]]
    All submitted batches that refer to pname:semaphore must: have completed
    execution
  * [[VUID-vkDestroySemaphore-semaphore-01138]]
    If sname:VkAllocationCallbacks were provided when pname:semaphore was
    created, a compatible set of callbacks must: be provided here
  * [[VUID-vkDestroySemaphore-semaphore-01139]]
    If no sname:VkAllocationCallbacks were provided when pname:semaphore was
    created, pname:pAllocator must: be `NULL`
****

include::{generated}/validity/protos/vkDestroySemaphore.txt[]
--


[[synchronization-semaphores-signaling]]
=== Semaphore Signaling

When a batch is submitted to a queue via a <<devsandqueues-submission, queue
submission>>, and it includes semaphores to be signaled, it defines a memory
dependency on the batch, and defines _semaphore signal operations_ which set
the semaphores to the signaled state.

ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
In case of semaphores created with a elink:VkSemaphoreType of
ename:VK_SEMAPHORE_TYPE_TIMELINE the semaphore is considered signaled with
respect to the counter value set to be signaled as specified in
slink:VkTimelineSemaphoreSubmitInfo or slink:VkSemaphoreSignalInfo.
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]

The first <<synchronization-dependencies-scopes, synchronization scope>>
includes every command submitted in the same batch.
ifdef::VK_KHR_synchronization2[]
In the case of flink:vkQueueSubmit2KHR, the first synchronization scope is
limited to the pipeline stage specified by
slink:VkSemaphoreSubmitInfoKHR::pname:stageMask.
endif::VK_KHR_synchronization2[]
Semaphore signal operations that are defined by flink:vkQueueSubmit
ifdef::VK_KHR_synchronization2[]
or flink:vkQueueSubmit2KHR
endif::VK_KHR_synchronization2[]
additionally include all commands that occur earlier in
<<synchronization-submission-order,submission order>>.
Semaphore signal operations that are defined by flink:vkQueueSubmit or
flink:vkQueueBindSparse additionally include in the first synchronization
scope any semaphore and fence signal operations that occur earlier in
<<synchronization-signal-operation-order,signal operation order>>.

The second <<synchronization-dependencies-scopes, synchronization scope>>
includes only the semaphore signal operation.

The first <<synchronization-dependencies-access-scopes, access scope>>
includes all memory access performed by the device.

The second <<synchronization-dependencies-access-scopes, access scope>> is
empty.


[[synchronization-semaphores-waiting]]
=== Semaphore Waiting

When a batch is submitted to a queue via a <<devsandqueues-submission, queue
submission>>, and it includes semaphores to be waited on, it defines a
memory dependency between prior semaphore signal operations and the batch,
and defines _semaphore wait operations_.

Such semaphore wait operations set the semaphores
ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
created with a elink:VkSemaphoreType of ename:VK_SEMAPHORE_TYPE_BINARY
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
to the unsignaled state.
ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
In case of semaphores created with a elink:VkSemaphoreType of
ename:VK_SEMAPHORE_TYPE_TIMELINE a prior semaphore signal operation defines
a memory dependency with a semaphore wait operation if the value the
semaphore is signaled with is greater than or equal to the value the
semaphore is waited with, thus the semaphore will continue to be considered
signaled with respect to the counter value waited on as specified in
slink:VkTimelineSemaphoreSubmitInfo.
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]

The first synchronization scope includes all semaphore signal operations
that operate on semaphores waited on in the same batch, and that
happen-before the wait completes.

The second <<synchronization-dependencies-scopes, synchronization scope>>
includes every command submitted in the same batch.
In the case of flink:vkQueueSubmit, the second synchronization scope is
limited to operations on the pipeline stages determined by the
<<synchronization-pipeline-stages-masks, destination stage mask>> specified
by the corresponding element of pname:pWaitDstStageMask.
ifdef::VK_KHR_synchronization2[]
In the case of flink:vkQueueSubmit2KHR, the second synchronization scope is
limited to the pipeline stage specified by
slink:VkSemaphoreSubmitInfoKHR::pname:stageMask.
endif::VK_KHR_synchronization2[]
Also, in the case of
ifdef::VK_KHR_synchronization2[]
either flink:vkQueueSubmit2KHR or
endif::VK_KHR_synchronization2[]
flink:vkQueueSubmit, the second synchronization scope additionally includes
all commands that occur later in
<<synchronization-submission-order,submission order>>.

The first <<synchronization-dependencies-access-scopes, access scope>> is
empty.

The second <<synchronization-dependencies-access-scopes, access scope>>
includes all memory access performed by the device.

The semaphore wait operation happens-after the first set of operations in
the execution dependency, and happens-before the second set of operations in
the execution dependency.

[NOTE]
.Note
====
Unlike
ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
timeline semaphores,
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
fences or events, the act of waiting for a binary semaphore also unsignals
that semaphore.
Applications must: ensure that between two such wait operations, the
semaphore is signaled again, with execution dependencies used to ensure
these occur in order.
Binary semaphore waits and signals should thus occur in discrete 1:1 pairs.
====

ifdef::VK_KHR_swapchain[]
[NOTE]
.Note
====
A common scenario for using pname:pWaitDstStageMask with values other than
ename:VK_PIPELINE_STAGE_ALL_COMMANDS_BIT is when synchronizing a window
system presentation operation against subsequent command buffers which
render the next frame.
In this case, a presentation image must: not be overwritten until the
presentation operation completes, but other pipeline stages can: execute
without waiting.
A mask of ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT prevents
subsequent color attachment writes from executing until the semaphore
signals.
Some implementations may: be able to execute transfer operations and/or
pre-rasterization work before the semaphore is signaled.

If an image layout transition needs to be performed on a presentable image
before it is used in a framebuffer, that can: be performed as the first
operation submitted to the queue after acquiring the image, and should: not
prevent other work from overlapping with the presentation operation.
For example, a sname:VkImageMemoryBarrier could use:

  * pname:srcStageMask = ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT
  * pname:srcAccessMask = 0
  * pname:dstStageMask = ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT
  * pname:dstAccessMask = ename:VK_ACCESS_COLOR_ATTACHMENT_READ_BIT |
    ename:VK_ACCESS_COLOR_ATTACHMENT_WRITE_BIT.
  * pname:oldLayout = ename:VK_IMAGE_LAYOUT_PRESENT_SRC_KHR
  * pname:newLayout = ename:VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL

Alternatively, pname:oldLayout can: be ename:VK_IMAGE_LAYOUT_UNDEFINED, if
the image's contents need not be preserved.

This barrier accomplishes a dependency chain between previous presentation
operations and subsequent color attachment output operations, with the
layout transition performed in between, and does not introduce a dependency
between previous work and any
<<pipeline-graphics-subsets-pre-rasterization,pre-rasterization shader
stage>>s.
More precisely, the semaphore signals after the presentation operation
completes, the semaphore wait stalls the
ename:VK_PIPELINE_STAGE_COLOR_ATTACHMENT_OUTPUT_BIT stage, and there is a
dependency from that same stage to itself with the layout transition
performed in between.
====
endif::VK_KHR_swapchain[]


[[synchronization-semaphores-waiting-state]]
=== Semaphore State Requirements For Wait Operations

Before waiting on a semaphore, the application must: ensure the semaphore is
in a valid state for a wait operation.
Specifically, when a <<synchronization-semaphores-waiting,semaphore wait
operation>> is submitted to a queue:

  * A binary semaphore must: be signaled, or have an associated
    <<synchronization-semaphores-signaling,semaphore signal operation>> that
    is pending execution.
  * Any <<synchronization-semaphores-signaling,semaphore signal operations>>
    on which the pending binary semaphore signal operation depends must:
    also be completed or pending execution.
  * There must: be no other queue waiting on the same binary semaphore when
    the operation executes.


ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
[[synchronization-semaphores-hostops]]
=== Host Operations on Semaphores

In addition to <<synchronization-semaphores-signaling,semaphore signal
operations>> and <<synchronization-semaphores-waiting,semaphore wait
operations>> submitted to device queues, timeline semaphores support the
following host operations:

  * Query the current counter value of the semaphore using the
    flink:vkGetSemaphoreCounterValue command.
  * Wait for a set of semaphores to reach particular counter values using
    the flink:vkWaitSemaphores command.
  * Signal the semaphore with a particular counter value from the host using
    the flink:vkSignalSemaphore command.

[open,refpage='vkGetSemaphoreCounterValue',desc='Query the current state of a timeline semaphore',type='protos',alias='vkGetSemaphoreCounterValueKHR']
--
To query the current counter value of a semaphore created with a
elink:VkSemaphoreType of ename:VK_SEMAPHORE_TYPE_TIMELINE from the host,
call:

ifdef::VK_VERSION_1_2[]
include::{generated}/api/protos/vkGetSemaphoreCounterValue.txt[]
endif::VK_VERSION_1_2[]

ifdef::VK_VERSION_1_2+VK_KHR_timeline_semaphore[or the equivalent command]

ifdef::VK_KHR_timeline_semaphore[]
include::{generated}/api/protos/vkGetSemaphoreCounterValueKHR.txt[]
endif::VK_KHR_timeline_semaphore[]

  * pname:device is the logical device that owns the semaphore.
  * pname:semaphore is the handle of the semaphore to query.
  * pname:pValue is a pointer to a 64-bit integer value in which the current
    counter value of the semaphore is returned.

[NOTE]
.Note
====
If a <<devsandqueues-submission, queue submission>> command is pending
execution, then the value returned by this command may: immediately be out
of date.
====

.Valid Usage
****
  * [[VUID-vkGetSemaphoreCounterValue-semaphore-03255]]
    pname:semaphore must: have been created with a elink:VkSemaphoreType of
    ename:VK_SEMAPHORE_TYPE_TIMELINE
****

include::{generated}/validity/protos/vkGetSemaphoreCounterValue.txt[]
--

[open,refpage='vkWaitSemaphores',desc='Wait for timeline semaphores on the host',type='protos',alias='vkWaitSemaphoresKHR']
--
To wait for a set of semaphores created with a elink:VkSemaphoreType of
ename:VK_SEMAPHORE_TYPE_TIMELINE to reach particular counter values on the
host, call:

ifdef::VK_VERSION_1_2[]
include::{generated}/api/protos/vkWaitSemaphores.txt[]
endif::VK_VERSION_1_2[]

ifdef::VK_VERSION_1_2+VK_KHR_timeline_semaphore[or the equivalent command]

ifdef::VK_KHR_timeline_semaphore[]
include::{generated}/api/protos/vkWaitSemaphoresKHR.txt[]
endif::VK_KHR_timeline_semaphore[]

  * pname:device is the logical device that owns the semaphores.
  * pname:pWaitInfo is a pointer to a slink:VkSemaphoreWaitInfo structure
    containing information about the wait condition.
  * pname:timeout is the timeout period in units of nanoseconds.
    pname:timeout is adjusted to the closest value allowed by the
    implementation-dependent timeout accuracy, which may: be substantially
    longer than one nanosecond, and may: be longer than the requested
    period.

If the condition is satisfied when fname:vkWaitSemaphores is called, then
fname:vkWaitSemaphores returns immediately.
If the condition is not satisfied at the time fname:vkWaitSemaphores is
called, then fname:vkWaitSemaphores will block and wait until the condition
is satisfied or the pname:timeout has expired, whichever is sooner.

If pname:timeout is zero, then fname:vkWaitSemaphores does not wait, but
simply returns information about the current state of the semaphores.
ename:VK_TIMEOUT will be returned in this case if the condition is not
satisfied, even though no actual wait was performed.

If the condition is satisfied before the pname:timeout has expired,
fname:vkWaitSemaphores returns ename:VK_SUCCESS.
Otherwise, fname:vkWaitSemaphores returns ename:VK_TIMEOUT after the
pname:timeout has expired.

If device loss occurs (see <<devsandqueues-lost-device,Lost Device>>) before
the timeout has expired, fname:vkWaitSemaphores must: return in finite time
with either ename:VK_SUCCESS or ename:VK_ERROR_DEVICE_LOST.

include::{generated}/validity/protos/vkWaitSemaphores.txt[]
--

[open,refpage='VkSemaphoreWaitInfo',desc='Structure containing information about the semaphore wait condition',type='structs',alias='VkSemaphoreWaitInfoKHR']
--
The sname:VkSemaphoreWaitInfo structure is defined as:

include::{generated}/api/structs/VkSemaphoreWaitInfo.txt[]

ifdef::VK_KHR_timeline_semaphore[]
or the equivalent

include::{generated}/api/structs/VkSemaphoreWaitInfoKHR.txt[]
endif::VK_KHR_timeline_semaphore[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:flags is a bitmask of elink:VkSemaphoreWaitFlagBits specifying
    additional parameters for the semaphore wait operation.
  * pname:semaphoreCount is the number of semaphores to wait on.
  * pname:pSemaphores is a pointer to an array of pname:semaphoreCount
    semaphore handles to wait on.
  * pname:pValues is a pointer to an array of pname:semaphoreCount timeline
    semaphore values.

.Valid Usage
****
  * [[VUID-VkSemaphoreWaitInfo-pSemaphores-03256]]
    All of the elements of pname:pSemaphores must: reference a semaphore
    that was created with a elink:VkSemaphoreType of
    ename:VK_SEMAPHORE_TYPE_TIMELINE
****

include::{generated}/validity/structs/VkSemaphoreWaitInfo.txt[]
--

[open,refpage='VkSemaphoreWaitFlagBits',desc='Bitmask specifying additional parameters of a semaphore wait operation',type='enums',alias='VkSemaphoreWaitFlagBitsKHR']
--
Bits which can: be set in slink:VkSemaphoreWaitInfo::pname:flags, specifying
additional parameters of a semaphore wait operation, are:

include::{generated}/api/enums/VkSemaphoreWaitFlagBits.txt[]

ifdef::VK_KHR_timeline_semaphore[]
or the equivalent

include::{generated}/api/enums/VkSemaphoreWaitFlagBitsKHR.txt[]
endif::VK_KHR_timeline_semaphore[]

  * ename:VK_SEMAPHORE_WAIT_ANY_BIT specifies that the semaphore wait
    condition is that at least one of the semaphores in
    sname:VkSemaphoreWaitInfo::pname:pSemaphores has reached the value
    specified by the corresponding element of
    sname:VkSemaphoreWaitInfo::pname:pValues.
    If ename:VK_SEMAPHORE_WAIT_ANY_BIT is not set, the semaphore wait
    condition is that all of the semaphores in
    sname:VkSemaphoreWaitInfo::pname:pSemaphores have reached the value
    specified by the corresponding element of
    sname:VkSemaphoreWaitInfo::pname:pValues.
--

[open,refpage='VkSemaphoreWaitFlags',desc='Bitmask of VkSemaphoreWaitFlagBits',type='flags',alias='VkSemaphoreWaitFlagsKHR']
--
include::{generated}/api/flags/VkSemaphoreWaitFlags.txt[]

ifdef::VK_KHR_timeline_semaphore[]
or the equivalent

include::{generated}/api/flags/VkSemaphoreWaitFlagsKHR.txt[]
endif::VK_KHR_timeline_semaphore[]

tname:VkSemaphoreWaitFlags is a bitmask type for setting a mask of zero or
more elink:VkSemaphoreWaitFlagBits.
--

[open,refpage='vkSignalSemaphore',desc='Signal a timeline semaphore on the host',type='protos',alias='vkSignalSemaphoreKHR']
--
To signal a semaphore created with a elink:VkSemaphoreType of
ename:VK_SEMAPHORE_TYPE_TIMELINE with a particular counter value, on the
host, call:

ifdef::VK_VERSION_1_2[]
include::{generated}/api/protos/vkSignalSemaphore.txt[]
endif::VK_VERSION_1_2[]

ifdef::VK_VERSION_1_2+VK_KHR_timeline_semaphore[or the equivalent command]

ifdef::VK_KHR_timeline_semaphore[]
include::{generated}/api/protos/vkSignalSemaphoreKHR.txt[]
endif::VK_KHR_timeline_semaphore[]

  * pname:device is the logical device that owns the semaphore.
  * pname:pSignalInfo is a pointer to a slink:VkSemaphoreSignalInfo
    structure containing information about the signal operation.

When fname:vkSignalSemaphore is executed on the host, it defines and
immediately executes a <<synchronization-semaphores-signaling,_semaphore
signal operation_>> which sets the timeline semaphore to the given value.

The first synchronization scope is defined by the host execution model, but
includes execution of fname:vkSignalSemaphore on the host and anything that
happened-before it.

The second synchronization scope is empty.

include::{generated}/validity/protos/vkSignalSemaphore.txt[]
--

[open,refpage='VkSemaphoreSignalInfo',desc='Structure containing information about a semaphore signal operation',type='structs',alias='VkSemaphoreSignalInfoKHR']
--
The sname:VkSemaphoreSignalInfo structure is defined as:

include::{generated}/api/structs/VkSemaphoreSignalInfo.txt[]

ifdef::VK_KHR_timeline_semaphore[]
or the equivalent

include::{generated}/api/structs/VkSemaphoreSignalInfoKHR.txt[]
endif::VK_KHR_timeline_semaphore[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:semaphore is the handle of the semaphore to signal.
  * pname:value is the value to signal.

.Valid Usage
****
  * [[VUID-VkSemaphoreSignalInfo-semaphore-03257]]
    pname:semaphore must: have been created with a elink:VkSemaphoreType of
    ename:VK_SEMAPHORE_TYPE_TIMELINE
  * [[VUID-VkSemaphoreSignalInfo-value-03258]]
    pname:value must: have a value greater than the current value of the
    semaphore
  * [[VUID-VkSemaphoreSignalInfo-value-03259]]
    pname:value must: be less than the value of any pending semaphore signal
    operations
  * [[VUID-VkSemaphoreSignalInfo-value-03260]]
    pname:value must: have a value which does not differ from the current
    value of the semaphore or the value of any outstanding semaphore wait or
    signal operation on pname:semaphore by more than
    <<limits-maxTimelineSemaphoreValueDifference,
    pname:maxTimelineSemaphoreValueDifference>>
****

include::{generated}/validity/structs/VkSemaphoreSignalInfo.txt[]
--
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]


ifdef::VK_VERSION_1_1,VK_KHR_external_semaphore[]
[[synchronization-semaphores-importing]]
=== Importing Semaphore Payloads

Applications can: import a semaphore payload into an existing semaphore
using an external semaphore handle.
The effects of the import operation will be either temporary or permanent,
as specified by the application.
If the import is temporary, the implementation must: restore the semaphore
to its prior permanent state after submitting the next semaphore wait
operation.
Performing a subsequent temporary import on a semaphore before performing a
semaphore wait has no effect on this requirement; the next wait submitted on
the semaphore must: still restore its last permanent state.
A permanent payload import behaves as if the target semaphore was destroyed,
and a new semaphore was created with the same handle but the imported
payload.
Because importing a semaphore payload temporarily or permanently detaches
the existing payload from a semaphore, similar usage restrictions to those
applied to fname:vkDestroySemaphore are applied to any command that imports
a semaphore payload.
Which of these import types is used is referred to as the import operation's
_permanence_.
Each handle type supports either one or both types of permanence.

The implementation must: perform the import operation by either referencing
or copying the payload referred to by the specified external semaphore
handle, depending on the handle's type.
The import method used is referred to as the handle type's _transference_.
When using handle types with reference transference, importing a payload to
a semaphore adds the semaphore to the set of all semaphores sharing that
payload.
This set includes the semaphore from which the payload was exported.
Semaphore signaling and waiting operations performed on any semaphore in the
set must: behave as if the set were a single semaphore.
Importing a payload using handle types with copy transference creates a
duplicate copy of the payload at the time of import, but makes no further
reference to it.
Semaphore signaling and waiting operations performed on the target of copy
imports must: not affect any other semaphore or payload.

Export operations have the same transference as the specified handle type's
import operations.
Additionally, exporting a semaphore payload to a handle with copy
transference has the same side effects on the source semaphore's payload as
executing a semaphore wait operation.
If the semaphore was using a temporarily imported payload, the semaphore's
prior permanent payload will be restored.

ifdef::VK_KHR_external_semaphore_win32,VK_KHR_external_semaphore_fd,VK_FUCHSIA_external_semaphore[]
[NOTE]
.Note
====
The permanence and transference of handle types can be found in:

ifdef::VK_KHR_external_semaphore_win32[]
  * <<synchronization-semaphore-handletypes-win32,Handle Types Supported by
    sname:VkImportSemaphoreWin32HandleInfoKHR>>
endif::VK_KHR_external_semaphore_win32[]
ifdef::VK_KHR_external_semaphore_fd[]
  * <<synchronization-semaphore-handletypes-fd,Handle Types Supported by
    sname:VkImportSemaphoreFdInfoKHR>>
endif::VK_KHR_external_semaphore_fd[]
ifdef::VK_FUCHSIA_external_semaphore[]
  * <<synchronization-semaphore-handletypes-fuchsia,Handle Types Supported
    by sname:VkImportSemaphoreZirconHandleInfoFUCHSIA>>
endif::VK_FUCHSIA_external_semaphore[]
====
endif::VK_KHR_external_semaphore_win32,VK_KHR_external_semaphore_fd,VK_FUCHSIA_external_semaphore[]

<<fundamentals-threadingbehavior,External synchronization>> allows
implementations to modify an object's internal state, i.e. payload, without
internal synchronization.
However, for semaphores sharing a payload across processes, satisfying the
external synchronization requirements of sname:VkSemaphore parameters as if
all semaphores in the set were the same object is sometimes infeasible.
Satisfying the <<synchronization-semaphores-waiting-state,wait operation
state requirements>> would similarly require impractical coordination or
levels of trust between processes.
Therefore, these constraints only apply to a specific semaphore handle, not
to its payload.
For distinct semaphore objects which share a payload, if the semaphores are
passed to separate queue submission commands concurrently, behavior will be
as if the commands were called in an arbitrary sequential order.
If the <<synchronization-semaphores-waiting-state,wait operation state
requirements>> are violated for the shared payload by a queue submission
command, or if a signal operation is queued for a shared payload that is
already signaled or has a pending signal operation, effects must: be limited
to one or more of the following:

  * Returning ename:VK_ERROR_INITIALIZATION_FAILED from the command which
    resulted in the violation.
  * Losing the logical device on which the violation occurred immediately or
    at a future time, resulting in a ename:VK_ERROR_DEVICE_LOST error from
    subsequent commands, including the one causing the violation.
  * Continuing execution of the violating command or operation as if the
    semaphore wait completed successfully after an implementation-dependent
    timeout.
    In this case, the state of the payload becomes undefined:, and future
    operations on semaphores sharing the payload will be subject to these
    same rules.
    The semaphore must: be destroyed or have its payload replaced by an
    import operation to again have a well-defined state.

[NOTE]
.Note
====
These rules allow processes to synchronize access to shared memory without
trusting each other.
However, such processes must still be cautious not to use the shared
semaphore for more than synchronizing access to the shared memory.
For example, a process should not use a shared semaphore as part of an
execution dependency chain that, when complete, leads to objects being
destroyed, if it does not trust other processes sharing the semaphore
payload.
====

When a semaphore is using an imported payload, its
slink:VkExportSemaphoreCreateInfo::pname:handleTypes value is specified when
creating the semaphore from which the payload was exported, rather than
specified when creating the semaphore.
Additionally,
slink:VkExternalSemaphoreProperties::pname:exportFromImportedHandleTypes
restricts which handle types can: be exported from such a semaphore based on
the specific handle type used to import the current payload.
ifdef::VK_KHR_swapchain[]
Passing a semaphore to flink:vkAcquireNextImageKHR is equivalent to
temporarily importing a semaphore payload to that semaphore.

[NOTE]
.Note
====
Because the exportable handle types of an imported semaphore correspond to
its current imported payload, and flink:vkAcquireNextImageKHR behaves the
same as a temporary import operation for which the source semaphore is
opaque to the application, applications have no way of determining whether
any external handle types can: be exported from a semaphore in this state.
Therefore, applications must: not attempt to export external handles from
semaphores using a temporarily imported payload from
flink:vkAcquireNextImageKHR.
====
endif::VK_KHR_swapchain[]

When importing a semaphore payload, it is the responsibility of the
application to ensure the external handles meet all valid usage
requirements.
However, implementations must: perform sufficient validation of external
handles to ensure that the operation results in a valid semaphore which will
not cause program termination, device loss, queue stalls, or corruption of
other resources when used as allowed according to its import parameters, and
excepting those side effects allowed for violations of the
<<synchronization-semaphores-waiting-state,valid semaphore state for wait
operations>> rules.
If the external handle provided does not meet these requirements, the
implementation must: fail the semaphore payload import operation with the
error code ename:VK_ERROR_INVALID_EXTERNAL_HANDLE.

ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
In addition, when importing a semaphore payload that is not compatible with
the payload type corresponding to the elink:VkSemaphoreType the semaphore
was created with, the implementation may: fail the semaphore payload import
operation with the error code ename:VK_ERROR_INVALID_EXTERNAL_HANDLE.

[NOTE]
.Note
====
As the introduction of the external semaphore handle type
ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_D3D12_FENCE_BIT predates that of
timeline semaphores, support for importing semaphore payloads from external
handles of that type into semaphores created (implicitly or explicitly) with
a elink:VkSemaphoreType of ename:VK_SEMAPHORE_TYPE_BINARY is preserved for
backwards compatibility.
However, applications should: prefer importing such handle types into
semaphores created with a elink:VkSemaphoreType of
ename:VK_SEMAPHORE_TYPE_TIMELINE.
====
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
endif::VK_VERSION_1_1,VK_KHR_external_semaphore[]

ifdef::VK_KHR_external_semaphore_win32[]
[open,refpage='vkImportSemaphoreWin32HandleKHR',desc='Import a semaphore from a Windows HANDLE',type='protos']
--
To import a semaphore payload from a Windows handle, call:

include::{generated}/api/protos/vkImportSemaphoreWin32HandleKHR.txt[]

  * pname:device is the logical device that created the semaphore.
  * pname:pImportSemaphoreWin32HandleInfo is a pointer to a
    slink:VkImportSemaphoreWin32HandleInfoKHR structure specifying the
    semaphore and import parameters.

Importing a semaphore payload from Windows handles does not transfer
ownership of the handle to the Vulkan implementation.
For handle types defined as NT handles, the application must: release
ownership using the code:CloseHandle system call when the handle is no
longer needed.

Applications can: import the same semaphore payload into multiple instances
of Vulkan, into the same instance from which it was exported, and multiple
times into a given Vulkan instance.

include::{generated}/validity/protos/vkImportSemaphoreWin32HandleKHR.txt[]
--

[open,refpage='VkImportSemaphoreWin32HandleInfoKHR',desc='Structure specifying Windows handle to import to a semaphore',type='structs']
--
The sname:VkImportSemaphoreWin32HandleInfoKHR structure is defined as:

include::{generated}/api/structs/VkImportSemaphoreWin32HandleInfoKHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:semaphore is the semaphore into which the payload will be
    imported.
  * pname:flags is a bitmask of elink:VkSemaphoreImportFlagBits specifying
    additional parameters for the semaphore payload import operation.
  * pname:handleType is a elink:VkExternalSemaphoreHandleTypeFlagBits value
    specifying the type of pname:handle.
  * pname:handle is `NULL` or the external handle to import.
  * pname:name is `NULL` or a null-terminated UTF-16 string naming the
    underlying synchronization primitive to import.

The handle types supported by pname:handleType are:

[[synchronization-semaphore-handletypes-win32]]
.Handle Types Supported by sname:VkImportSemaphoreWin32HandleInfoKHR
[width="80%",options="header"]
|====
| Handle Type                                                      | Transference | Permanence Supported
| ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_OPAQUE_WIN32_BIT     | Reference    | Temporary,Permanent
| ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_OPAQUE_WIN32_KMT_BIT | Reference    | Temporary,Permanent
| ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_D3D12_FENCE_BIT      | Reference    | Temporary,Permanent
|====

.Valid Usage
****
  * [[VUID-VkImportSemaphoreWin32HandleInfoKHR-handleType-01140]]
    pname:handleType must: be a value included in the
    <<synchronization-semaphore-handletypes-win32,Handle Types Supported by
    sname:VkImportSemaphoreWin32HandleInfoKHR>> table
  * [[VUID-VkImportSemaphoreWin32HandleInfoKHR-handleType-01466]]
    If pname:handleType is not
    ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_OPAQUE_WIN32_BIT or
    ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_D3D12_FENCE_BIT, pname:name
    must: be `NULL`
  * [[VUID-VkImportSemaphoreWin32HandleInfoKHR-handleType-01467]]
    If pname:handle is `NULL`, pname:name must: name a valid synchronization
    primitive of the type specified by pname:handleType
  * [[VUID-VkImportSemaphoreWin32HandleInfoKHR-handleType-01468]]
    If pname:name is `NULL`, pname:handle must: be a valid handle of the
    type specified by pname:handleType
  * [[VUID-VkImportSemaphoreWin32HandleInfoKHR-handle-01469]]
    If pname:handle is not `NULL`, pname:name must: be `NULL`
  * [[VUID-VkImportSemaphoreWin32HandleInfoKHR-handle-01542]]
    If pname:handle is not `NULL`, it must: obey any requirements listed for
    pname:handleType in
    <<external-semaphore-handle-types-compatibility,external semaphore
    handle types compatibility>>
  * [[VUID-VkImportSemaphoreWin32HandleInfoKHR-name-01543]]
    If pname:name is not `NULL`, it must: obey any requirements listed for
    pname:handleType in
    <<external-semaphore-handle-types-compatibility,external semaphore
    handle types compatibility>>
  * [[VUID-VkImportSemaphoreWin32HandleInfoKHR-handleType-03261]]
    If pname:handleType is
    ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_OPAQUE_WIN32_BIT or
    ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_OPAQUE_WIN32_KMT_BIT, the
    slink:VkSemaphoreCreateInfo::pname:flags field must: match that of the
    semaphore from which pname:handle or pname:name was exported
ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
  * [[VUID-VkImportSemaphoreWin32HandleInfoKHR-handleType-03262]]
    If pname:handleType is
    ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_OPAQUE_WIN32_BIT or
    ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_OPAQUE_WIN32_KMT_BIT, the
    slink:VkSemaphoreTypeCreateInfo::pname:semaphoreType field must: match
    that of the semaphore from which pname:handle or pname:name was exported
  * [[VUID-VkImportSemaphoreWin32HandleInfoKHR-flags-03322]]
    If pname:flags contains ename:VK_SEMAPHORE_IMPORT_TEMPORARY_BIT, the
    slink:VkSemaphoreTypeCreateInfo::pname:semaphoreType field of the
    semaphore from which pname:handle or pname:name was exported must: not
    be ename:VK_SEMAPHORE_TYPE_TIMELINE
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
****

include::{generated}/validity/structs/VkImportSemaphoreWin32HandleInfoKHR.txt[]
--
endif::VK_KHR_external_semaphore_win32[]

ifdef::VK_KHR_external_semaphore_fd[]
[open,refpage='vkImportSemaphoreFdKHR',desc='Import a semaphore from a POSIX file descriptor',type='protos']
--
To import a semaphore payload from a POSIX file descriptor, call:

include::{generated}/api/protos/vkImportSemaphoreFdKHR.txt[]

  * pname:device is the logical device that created the semaphore.
  * pname:pImportSemaphoreFdInfo is a pointer to a
    slink:VkImportSemaphoreFdInfoKHR structure specifying the semaphore and
    import parameters.

Importing a semaphore payload from a file descriptor transfers ownership of
the file descriptor from the application to the Vulkan implementation.
The application must: not perform any operations on the file descriptor
after a successful import.

Applications can: import the same semaphore payload into multiple instances
of Vulkan, into the same instance from which it was exported, and multiple
times into a given Vulkan instance.

.Valid Usage
****
  * [[VUID-vkImportSemaphoreFdKHR-semaphore-01142]]
    pname:semaphore must: not be associated with any queue command that has
    not yet completed execution on that queue
****

include::{generated}/validity/protos/vkImportSemaphoreFdKHR.txt[]
--

[open,refpage='VkImportSemaphoreFdInfoKHR',desc='Structure specifying POSIX file descriptor to import to a semaphore',type='structs']
--
The sname:VkImportSemaphoreFdInfoKHR structure is defined as:

include::{generated}/api/structs/VkImportSemaphoreFdInfoKHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:semaphore is the semaphore into which the payload will be
    imported.
  * pname:flags is a bitmask of elink:VkSemaphoreImportFlagBits specifying
    additional parameters for the semaphore payload import operation.
  * pname:handleType is a elink:VkExternalSemaphoreHandleTypeFlagBits value
    specifying the type of pname:fd.
  * pname:fd is the external handle to import.

The handle types supported by pname:handleType are:

[[synchronization-semaphore-handletypes-fd]]
.Handle Types Supported by sname:VkImportSemaphoreFdInfoKHR
[width="80%",options="header"]
|====
| Handle Type                                               | Transference | Permanence Supported
| ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_OPAQUE_FD_BIT | Reference    | Temporary,Permanent
| ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_SYNC_FD_BIT   | Copy         | Temporary
|====

.Valid Usage
****
  * [[VUID-VkImportSemaphoreFdInfoKHR-handleType-01143]]
    pname:handleType must: be a value included in the
    <<synchronization-semaphore-handletypes-fd,Handle Types Supported by
    sname:VkImportSemaphoreFdInfoKHR>> table
  * [[VUID-VkImportSemaphoreFdInfoKHR-fd-01544]]
    pname:fd must: obey any requirements listed for pname:handleType in
    <<external-semaphore-handle-types-compatibility,external semaphore
    handle types compatibility>>
  * [[VUID-VkImportSemaphoreFdInfoKHR-handleType-03263]]
    If pname:handleType is
    ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_OPAQUE_FD_BIT, the
    slink:VkSemaphoreCreateInfo::pname:flags field must: match that of the
    semaphore from which pname:fd was exported
ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
  * [[VUID-VkImportSemaphoreFdInfoKHR-handleType-03264]]
    If pname:handleType is
    ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_OPAQUE_FD_BIT, the
    slink:VkSemaphoreTypeCreateInfo::pname:semaphoreType field must: match
    that of the semaphore from which pname:fd was exported
  * [[VUID-VkImportSemaphoreFdInfoKHR-flags-03323]]
    If pname:flags contains ename:VK_SEMAPHORE_IMPORT_TEMPORARY_BIT, the
    slink:VkSemaphoreTypeCreateInfo::pname:semaphoreType field of the
    semaphore from which pname:fd was exported must: not be
    ename:VK_SEMAPHORE_TYPE_TIMELINE
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
****

If pname:handleType is ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_SYNC_FD_BIT,
the special value `-1` for pname:fd is treated like a valid sync file
descriptor referring to an object that has already signaled.
The import operation will succeed and the sname:VkSemaphore will have a
temporarily imported payload as if a valid file descriptor had been
provided.

[NOTE]
.Note
====
This special behavior for importing an invalid sync file descriptor allows
easier interoperability with other system APIs which use the convention that
an invalid sync file descriptor represents work that has already completed
and does not need to be waited for.
It is consistent with the option for implementations to return a `-1` file
descriptor when exporting a
ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_SYNC_FD_BIT from a sname:VkSemaphore
which is signaled.
====

include::{generated}/validity/structs/VkImportSemaphoreFdInfoKHR.txt[]
--
endif::VK_KHR_external_semaphore_fd[]

ifdef::VK_FUCHSIA_external_semaphore[]
[open,refpage='vkImportSemaphoreZirconHandleFUCHSIA',desc='Import a semaphore from a Zircon event handle',type='protos']
--
To import a semaphore payload from a Zircon event handle, call:

include::{generated}/api/protos/vkImportSemaphoreZirconHandleFUCHSIA.txt[]

  * pname:device is the logical device that created the semaphore.
  * pname:pImportSemaphoreZirconHandleInfo is a pointer to a
    slink:VkImportSemaphoreZirconHandleInfoFUCHSIA structure specifying the
    semaphore and import parameters.

Importing a semaphore payload from a Zircon event handle transfers ownership
of the handle from the application to the Vulkan implementation.
The application must: not perform any operations on the handle after a
successful import.

Applications can: import the same semaphore payload into multiple instances
of Vulkan, into the same instance from which it was exported, and multiple
times into a given Vulkan instance.

.Valid Usage
****
  * [[VUID-vkImportSemaphoreZirconHandleFUCHSIA-semaphore-04764]]
    pname:semaphore must: not be associated with any queue command that has
    not yet completed execution on that queue
****

include::{generated}/validity/protos/vkImportSemaphoreZirconHandleFUCHSIA.txt[]
--

[open,refpage='VkImportSemaphoreZirconHandleInfoFUCHSIA',desc='Structure specifying Zircon event handle to import to a semaphore',type='structs']
--
The sname:VkImportSemaphoreZirconHandleInfoFUCHSIA structure is defined as:

include::{generated}/api/structs/VkImportSemaphoreZirconHandleInfoFUCHSIA.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:semaphore is the semaphore into which the payload will be
    imported.
  * pname:flags is a bitmask of elink:VkSemaphoreImportFlagBits specifying
    additional parameters for the semaphore payload import operation.
  * pname:handleType is a elink:VkExternalSemaphoreHandleTypeFlagBits value
    specifying the type of pname:zirconHandle.
  * pname:zirconHandle is the external handle to import.

The handle types supported by pname:handleType are:

[[synchronization-semaphore-handletypes-fuchsia]]
.Handle Types Supported by sname:VkImportSemaphoreZirconHandleInfoFUCHSIA
[width="80%",options="header"]
|====
| Handle Type                                               | Transference | Permanence Supported
| ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_ZIRCON_EVENT_BIT_FUCHSIA   | Reference         | Temporary,Permanent
|====

.Valid Usage
****
  * [[VUID-VkImportSemaphoreZirconHandleInfoFUCHSIA-handleType-04765]]
    pname:handleType must: be a value included in the
    <<synchronization-semaphore-handletypes-fuchsia,Handle Types Supported
    by sname:VkImportSemaphoreZirconHandleInfoFUCHSIA>> table
  * [[VUID-VkImportSemaphoreZirconHandleInfoFUCHSIA-zirconHandle-04766]]
    pname:zirconHandle must: obey any requirements listed for
    pname:handleType in
    <<external-semaphore-handle-types-compatibility,external semaphore
    handle types compatibility>>
  * [[VUID-VkImportSemaphoreZirconHandleInfoFUCHSIA-zirconHandle-04767]]
    pname:zirconHandle must: have code:ZX_RIGHTS_BASIC and
    code:ZX_RIGHTS_SIGNAL rights
ifdef::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
  * [[VUID-VkImportSemaphoreZirconHandleInfoFUCHSIA-semaphoreType-04768]]
    The slink:VkSemaphoreTypeCreateInfo::pname:semaphoreType field must: not
    be ename:VK_SEMAPHORE_TYPE_TIMELINE
endif::VK_VERSION_1_2,VK_KHR_timeline_semaphore[]
****

include::{generated}/validity/structs/VkImportSemaphoreZirconHandleInfoFUCHSIA.txt[]
--
endif::VK_FUCHSIA_external_semaphore[]

ifdef::VK_VERSION_1_1,VK_KHR_external_semaphore[]
ifdef::VK_KHR_external_semaphore_win32,VK_KHR_external_semaphore_fd,VK_FUCHSIA_external_semaphore[]
[open,refpage='VkSemaphoreImportFlagBits',desc='Bitmask specifying additional parameters of semaphore payload import',type='enums']
--
Bits which can: be set in

ifdef::VK_KHR_external_semaphore_win32[]
  * slink:VkImportSemaphoreWin32HandleInfoKHR::pname:flags
endif::VK_KHR_external_semaphore_win32[]
ifdef::VK_KHR_external_semaphore_fd[]
  * slink:VkImportSemaphoreFdInfoKHR::pname:flags
endif::VK_KHR_external_semaphore_fd[]
ifdef::VK_FUCHSIA_external_semaphore[]
  * slink:VkImportSemaphoreZirconHandleInfoFUCHSIA::pname:flags
endif::VK_FUCHSIA_external_semaphore[]

specifying additional parameters of a semaphore import operation are:

include::{generated}/api/enums/VkSemaphoreImportFlagBits.txt[]

ifdef::VK_KHR_external_semaphore[]
or the equivalent

include::{generated}/api/enums/VkSemaphoreImportFlagBitsKHR.txt[]
endif::VK_KHR_external_semaphore[]

These bits have the following meanings:

  * ename:VK_SEMAPHORE_IMPORT_TEMPORARY_BIT specifies that the semaphore
    payload will be imported only temporarily, as described in
    <<synchronization-semaphores-importing,Importing Semaphore Payloads>>,
    regardless of the permanence of pname:handleType.
--

[open,refpage='VkSemaphoreImportFlags',desc='Bitmask of VkSemaphoreImportFlagBits',type='flags']
--
include::{generated}/api/flags/VkSemaphoreImportFlags.txt[]

ifdef::VK_KHR_external_semaphore[]
or the equivalent

include::{generated}/api/flags/VkSemaphoreImportFlagsKHR.txt[]
endif::VK_KHR_external_semaphore[]

tname:VkSemaphoreImportFlags is a bitmask type for setting a mask of zero or
more elink:VkSemaphoreImportFlagBits.
--
endif::VK_KHR_external_semaphore_win32,VK_KHR_external_semaphore_fd,VK_FUCHSIA_external_semaphore[]
endif::VK_VERSION_1_1,VK_KHR_external_semaphore[]


[[synchronization-events]]
== Events

[open,refpage='VkEvent',desc='Opaque handle to an event object',type='handles']
--
Events are a synchronization primitive that can: be used to insert a
fine-grained dependency between commands submitted to the same queue, or
between the host and a queue.
Events must: not be used to insert a dependency between commands submitted
to different queues.
Events have two states - signaled and unsignaled.
An application can: signal or unsignal an event either on the host or on the
device.
A device can: be made to wait for an event to become signaled before
executing further operations.
No command exists to wait for an event to become signaled on the host, but
the current state of an event can: be queried.

Events are represented by sname:VkEvent handles:

include::{generated}/api/handles/VkEvent.txt[]
--

[open,refpage='vkCreateEvent',desc='Create a new event object',type='protos']
--
To create an event, call:

include::{generated}/api/protos/vkCreateEvent.txt[]

  * pname:device is the logical device that creates the event.
  * pname:pCreateInfo is a pointer to a slink:VkEventCreateInfo structure
    containing information about how the event is to be created.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.
  * pname:pEvent is a pointer to a handle in which the resulting event
    object is returned.

When created, the event object is in the unsignaled state.

ifdef::VK_KHR_portability_subset[]
.Valid Usage
****
  * [[VUID-vkCreateEvent-events-04468]]
    If the `apiext:VK_KHR_portability_subset` extension is enabled, and
    slink:VkPhysicalDevicePortabilitySubsetFeaturesKHR::pname:events is
    ename:VK_FALSE, then the implementation does not support
    <<synchronization-events, events>>, and flink:vkCreateEvent must: not be
    used
****
endif::VK_KHR_portability_subset[]

include::{generated}/validity/protos/vkCreateEvent.txt[]
--

[open,refpage='VkEventCreateInfo',desc='Structure specifying parameters of a newly created event',type='structs']
--
The sname:VkEventCreateInfo structure is defined as:

include::{generated}/api/structs/VkEventCreateInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:flags is a bitmask of elink:VkEventCreateFlagBits defining
    additional creation parameters.

include::{generated}/validity/structs/VkEventCreateInfo.txt[]
--

[open,refpage='VkEventCreateFlagBits',desc='Event creation flag bits',type='enums']
--
include::{generated}/api/enums/VkEventCreateFlagBits.txt[]

ifndef::VK_KHR_synchronization2[]
All values for this enum are defined by extensions.
endif::VK_KHR_synchronization2[]
ifdef::VK_KHR_synchronization2[]
  * ename:VK_EVENT_CREATE_DEVICE_ONLY_BIT_KHR specifies that host event
    commands will not be used with this event.
endif::VK_KHR_synchronization2[]
--

[open,refpage='VkEventCreateFlags',desc='Bitmask of event creation flag bits',type='flags']
--
include::{generated}/api/flags/VkEventCreateFlags.txt[]

tname:VkEventCreateFlags is a bitmask type for setting a mask of
elink:VkEventCreateFlagBits.
--

[open,refpage='vkDestroyEvent',desc='Destroy an event object',type='protos']
--
To destroy an event, call:

include::{generated}/api/protos/vkDestroyEvent.txt[]

  * pname:device is the logical device that destroys the event.
  * pname:event is the handle of the event to destroy.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.

.Valid Usage
****
  * [[VUID-vkDestroyEvent-event-01145]]
    All submitted commands that refer to pname:event must: have completed
    execution
  * [[VUID-vkDestroyEvent-event-01146]]
    If sname:VkAllocationCallbacks were provided when pname:event was
    created, a compatible set of callbacks must: be provided here
  * [[VUID-vkDestroyEvent-event-01147]]
    If no sname:VkAllocationCallbacks were provided when pname:event was
    created, pname:pAllocator must: be `NULL`
****

include::{generated}/validity/protos/vkDestroyEvent.txt[]
--

[open,refpage='vkGetEventStatus',desc='Retrieve the status of an event object',type='protos']
--
To query the state of an event from the host, call:

include::{generated}/api/protos/vkGetEventStatus.txt[]

  * pname:device is the logical device that owns the event.
  * pname:event is the handle of the event to query.

Upon success, fname:vkGetEventStatus returns the state of the event object
with the following return codes:

.Event Object Status Codes
[width="80%",options="header"]
|====
| Status | Meaning
| ename:VK_EVENT_SET | The event specified by pname:event is signaled.
| ename:VK_EVENT_RESET | The event specified by pname:event is unsignaled.
|====

If a fname:vkCmdSetEvent or fname:vkCmdResetEvent command is in a command
buffer that is in the <<commandbuffers-lifecycle, pending state>>, then the
value returned by this command may: immediately be out of date.

The state of an event can: be updated by the host.
The state of the event is immediately changed, and subsequent calls to
fname:vkGetEventStatus will return the new state.
If an event is already in the requested state, then updating it to the same
state has no effect.

ifdef::VK_KHR_synchronization2[]
.Valid Usage
****
 * [[VUID-vkGetEventStatus-event-03940]]
    pname:event must: not have been created with
    ename:VK_EVENT_CREATE_DEVICE_ONLY_BIT_KHR
****
endif::VK_KHR_synchronization2[]

include::{generated}/validity/protos/vkGetEventStatus.txt[]
--

[[synchronization-events-signaling-host]]
[open,refpage='vkSetEvent',desc='Set an event to signaled state',type='protos']
--
To set the state of an event to signaled from the host, call:

include::{generated}/api/protos/vkSetEvent.txt[]

  * pname:device is the logical device that owns the event.
  * pname:event is the event to set.

When flink:vkSetEvent is executed on the host, it defines an _event signal
operation_ which sets the event to the signaled state.

If pname:event is already in the signaled state when flink:vkSetEvent is
executed, then flink:vkSetEvent has no effect, and no event signal operation
occurs.

ifdef::VK_KHR_synchronization2[]
.Valid Usage
****
 * [[VUID-vkSetEvent-event-03941]]
   pname:event must: not have been created with
   ename:VK_EVENT_CREATE_DEVICE_ONLY_BIT_KHR
****
endif::VK_KHR_synchronization2[]

include::{generated}/validity/protos/vkSetEvent.txt[]
--

[[synchronization-events-unsignaling-host]]
[open,refpage='vkResetEvent',desc='Reset an event to non-signaled state',type='protos']
--
To set the state of an event to unsignaled from the host, call:

include::{generated}/api/protos/vkResetEvent.txt[]

  * pname:device is the logical device that owns the event.
  * pname:event is the event to reset.

When flink:vkResetEvent is executed on the host, it defines an _event
unsignal operation_ which resets the event to the unsignaled state.

If pname:event is already in the unsignaled state when flink:vkResetEvent is
executed, then flink:vkResetEvent has no effect, and no event unsignal
operation occurs.

.Valid Usage
****
  * [[VUID-vkResetEvent-event-03821]]
    There must: be an execution dependency between fname:vkResetEvent and
    the execution of any flink:vkCmdWaitEvents that includes pname:event in
    its pname:pEvents parameter
ifdef::VK_KHR_synchronization2[]
  * [[VUID-vkResetEvent-event-03822]]
    There must: be an execution dependency between fname:vkResetEvent and
    the execution of any flink:vkCmdWaitEvents2KHR that includes pname:event
    in its pname:pEvents parameter
endif::VK_KHR_synchronization2[]
ifdef::VK_KHR_synchronization2[]
  * [[VUID-vkResetEvent-event-03823]]
    pname:event must: not have been created with
    ename:VK_EVENT_CREATE_DEVICE_ONLY_BIT_KHR
endif::VK_KHR_synchronization2[]
****

include::{generated}/validity/protos/vkResetEvent.txt[]
--

The state of an event can: also be updated on the device by commands
inserted in command buffers.

[[synchronization-events-signaling-device]]
ifdef::VK_KHR_synchronization2[]
[open,refpage='vkCmdSetEvent2KHR',desc='Set an event object to signaled state',type='protos']
--
To signal an event from a device, call:

include::{generated}/api/protos/vkCmdSetEvent2KHR.txt[]

  * pname:commandBuffer is the command buffer into which the command is
    recorded.
  * pname:event is the event that will be signaled.
  * pname:pDependencyInfo is a pointer to a slink:VkDependencyInfoKHR
    structure defining the first scopes of this operation.

When flink:vkCmdSetEvent2KHR is submitted to a queue, it defines the first
half of memory dependencies defined by pname:pDependencyInfo, as well as an
event signal operation which sets the event to the signaled state.
A memory dependency is defined between the event signal operation and
commands that occur earlier in submission order.

The first <<synchronization-dependencies-scopes, synchronization scope>> and
<<synchronization-dependencies-access-scopes, access scope>> are defined by
the union of all the memory dependencies defined by pname:pDependencyInfo,
and are applied to all operations that occur earlier in
<<synchronization-submission-order,submission order>>.
<<synchronization-queue-transfers, Queue family ownership transfers>> and
<<synchronization-image-layout-transitions, image layout transitions>>
defined by pname:pDependencyInfo are also included in the first scopes.

The second <<synchronization-dependencies-scopes, synchronization scope>>
includes only the event signal operation, and any
<<synchronization-queue-transfers, queue family ownership transfers>> and
<<synchronization-image-layout-transitions, image layout transitions>>
defined by pname:pDependencyInfo.

The second <<synchronization-dependencies-access-scopes, access scope>>
includes only <<synchronization-queue-transfers, queue family ownership
transfers>> and <<synchronization-image-layout-transitions, image layout
transitions>>.

Future flink:vkCmdWaitEvents2KHR commands rely on all values of each element
in pname:pDependencyInfo matching exactly with those used to signal the
corresponding event.
flink:vkCmdWaitEvents must: not be used to wait on the result of a signal
operation defined by fname:vkCmdSetEvent2KHR.

[NOTE]
.Note
====
The extra information provided by flink:vkCmdSetEvent2KHR compared to
flink:vkCmdSetEvent allows implementations to more efficiently schedule the
operations required to satisfy the requested dependencies.
With flink:vkCmdSetEvent, the full dependency information is not known until
flink:vkCmdWaitEvents is recorded, forcing implementations to insert the
required operations at that point and not before.
====

If pname:event is already in the signaled state when flink:vkCmdSetEvent2KHR
is executed on the device, then flink:vkCmdSetEvent2KHR has no effect, no
event signal operation occurs, and no dependency is generated.

.Valid Usage
****
  * [[VUID-vkCmdSetEvent2KHR-synchronization2-03824]]
    The <<features-synchronization2, pname:synchronization2>> feature must:
    be enabled
  * [[VUID-vkCmdSetEvent2KHR-dependencyFlags-03825]]
    The pname:dependencyFlags member of pname:pDependencyInfo must: be `0`
ifdef::VK_VERSION_1_1,VK_KHR_device_group[]
  * [[VUID-vkCmdSetEvent2KHR-commandBuffer-03826]]
    The current device mask of pname:commandBuffer must: include exactly one
    physical device
endif::VK_VERSION_1_1,VK_KHR_device_group[]
  * [[VUID-vkCmdSetEvent2KHR-srcStageMask-03827]]
    The pname:srcStageMask member of any element of the
    pname:pMemoryBarriers, pname:pBufferMemoryBarriers, or
    pname:pImageMemoryBarriers members of pname:pDependencyInfo must: only
    include pipeline stages valid for the queue family that was used to
    create the command pool that pname:commandBuffer was allocated from
  * [[VUID-vkCmdSetEvent2KHR-dstStageMask-03828]]
    The pname:dstStageMask member of any element of the
    pname:pMemoryBarriers, pname:pBufferMemoryBarriers, or
    pname:pImageMemoryBarriers members of pname:pDependencyInfo must: only
    include pipeline stages valid for the queue family that was used to
    create the command pool that pname:commandBuffer was allocated from
****

include::{generated}/validity/protos/vkCmdSetEvent2KHR.txt[]
--

[open,refpage='VkDependencyInfoKHR',desc='Structure specifying dependency information for a synchronization command',type='structs']
--
The sname:VkDependencyInfoKHR structure is defined as:

include::{generated}/api/structs/VkDependencyInfoKHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:dependencyFlags is a bitmask of elink:VkDependencyFlagBits
    specifying how execution and memory dependencies are formed.
  * pname:memoryBarrierCount is the length of the pname:pMemoryBarriers
    array.
  * pname:pMemoryBarriers is a pointer to an array of
    slink:VkMemoryBarrier2KHR structures defining memory dependencies
    between any memory accesses.
  * pname:bufferMemoryBarrierCount is the length of the
    pname:pBufferMemoryBarriers array.
  * pname:pBufferMemoryBarriers is a pointer to an array of
    slink:VkBufferMemoryBarrier2KHR structures defining memory dependencies
    between buffer ranges.
  * pname:imageMemoryBarrierCount is the length of the
    pname:pImageMemoryBarriers array.
  * pname:pImageMemoryBarriers is a pointer to an array of
    slink:VkImageMemoryBarrier2KHR structures defining memory dependencies
    between image subresources.

This structure defines a set of <<synchronization-dependencies-memory,
memory dependencies>>, as well as <<synchronization-queue-transfers, queue
family transfer operations>> and <<synchronization-image-layout-transitions,
image layout transitions>>.

Each member of pname:pMemoryBarriers, pname:pBufferMemoryBarriers, and
pname:pImageMemoryBarriers defines a separate
<<synchronization-dependencies-memory, memory dependency>>.

include::{generated}/validity/structs/VkDependencyInfoKHR.txt[]
--
endif::VK_KHR_synchronization2[]

[open,refpage='vkCmdSetEvent',desc='Set an event object to signaled state',type='protos']
--
:refpage: vkCmdSetEvent

To set the state of an event to signaled from a device, call:

include::{generated}/api/protos/vkCmdSetEvent.txt[]

  * pname:commandBuffer is the command buffer into which the command is
    recorded.
  * pname:event is the event that will be signaled.
  * pname:stageMask specifies the <<synchronization-pipeline-stages,source
    stage mask>> used to determine the first
    <<synchronization-dependencies-scopes, synchronization scope>>.


ifdef::VK_KHR_synchronization2[]
fname:vkCmdSetEvent behaves identically to flink:vkCmdSetEvent2KHR, except
that it does not define an access scope, and must: only be used with
flink:vkCmdWaitEvents, not flink:vkCmdWaitEvents2KHR.
endif::VK_KHR_synchronization2[]

ifndef::VK_KHR_synchronization2[]
When flink:vkCmdSetEvent is submitted to a queue, it defines an execution
dependency on commands that were submitted before it, and defines an event
signal operation which sets the event to the signaled state.

The first <<synchronization-dependencies-scopes, synchronization scope>>
includes all commands that occur earlier in
<<synchronization-submission-order,submission order>>.
The synchronization scope is limited to operations on the pipeline stages
determined by the <<synchronization-pipeline-stages-masks, source stage
mask>> specified by pname:stageMask.

The second <<synchronization-dependencies-scopes, synchronization scope>>
includes only the event signal operation.

If pname:event is already in the signaled state when flink:vkCmdSetEvent is
executed on the device, then flink:vkCmdSetEvent has no effect, no event
signal operation occurs, and no execution dependency is generated.
endif::VK_KHR_synchronization2[]

.Valid Usage
****
:stageMaskName: stageMask
include::{chapters}/commonvalidity/stage_mask_common.txt[]
  * [[VUID-vkCmdSetEvent-stageMask-06457]]
    Any pipeline stage included in pname:stageMask must: be supported by the
    capabilities of the queue family specified by the pname:queueFamilyIndex
    member of the slink:VkCommandPoolCreateInfo structure that was used to
    create the sname:VkCommandPool that pname:commandBuffer was allocated
    from, as specified in the <<synchronization-pipeline-stages-supported,
    table of supported pipeline stages>>
  * [[VUID-vkCmdSetEvent-stageMask-01149]]
    pname:stageMask must: not include ename:VK_PIPELINE_STAGE_HOST_BIT
ifdef::VK_VERSION_1_1,VK_KHR_device_group[]
  * [[VUID-vkCmdSetEvent-commandBuffer-01152]]
    pname:commandBuffer's current device mask must: include exactly one
    physical device
endif::VK_VERSION_1_1,VK_KHR_device_group[]
****

include::{generated}/validity/protos/vkCmdSetEvent.txt[]
--

[[synchronization-events-unsignaling-device]]
ifdef::VK_KHR_synchronization2[]
[open,refpage='vkCmdResetEvent2KHR',desc='Reset an event object to non-signaled state',type='protos']
--
:refpage: vkCmdResetEvent2KHR

To unsignal the event from a device, call:

include::{generated}/api/protos/vkCmdResetEvent2KHR.txt[]

  * pname:commandBuffer is the command buffer into which the command is
    recorded.
  * pname:event is the event that will be unsignaled.
  * pname:stageMask is a tlink:VkPipelineStageFlags2KHR mask of pipeline
    stages used to determine the first
    <<synchronization-dependencies-scopes, synchronization scope>>.

When flink:vkCmdResetEvent2KHR is submitted to a queue, it defines an
execution dependency on commands that were submitted before it, and defines
an event unsignal operation which resets the event to the unsignaled state.

The first <<synchronization-dependencies-scopes, synchronization scope>>
includes all commands that occur earlier in
<<synchronization-submission-order,submission order>>.
The synchronization scope is limited to operations by pname:stageMask or
stages that are <<synchronization-pipeline-stages-order,logically earlier>>
than pname:stageMask.

The second <<synchronization-dependencies-scopes, synchronization scope>>
includes only the event unsignal operation.

If pname:event is already in the unsignaled state when
flink:vkCmdResetEvent2KHR is executed on the device, then this command has
no effect, no event unsignal operation occurs, and no execution dependency
is generated.

.Valid Usage
****
:stageMaskName: stageMask
include::{chapters}/commonvalidity/stage_mask_2_common.txt[]
  * [[VUID-vkCmdResetEvent2KHR-synchronization2-03829]]
    The <<features-synchronization2, pname:synchronization2>> feature must:
    be enabled
  * [[VUID-vkCmdResetEvent2KHR-stageMask-03830]]
    pname:stageMask must: not include ename:VK_PIPELINE_STAGE_2_HOST_BIT_KHR
  * [[VUID-vkCmdResetEvent2KHR-event-03831]]
    There must: be an execution dependency between fname:vkCmdResetEvent2KHR
    and the execution of any flink:vkCmdWaitEvents that includes pname:event
    in its pname:pEvents parameter
  * [[VUID-vkCmdResetEvent2KHR-event-03832]]
    There must: be an execution dependency between fname:vkCmdResetEvent2KHR
    and the execution of any flink:vkCmdWaitEvents2KHR that includes
    pname:event in its pname:pEvents parameter
ifdef::VK_VERSION_1_1,VK_KHR_device_group[]
  * [[VUID-vkCmdResetEvent2KHR-commandBuffer-03833]]
    pname:commandBuffer's current device mask must: include exactly one
    physical device
endif::VK_VERSION_1_1,VK_KHR_device_group[]
****

include::{generated}/validity/protos/vkCmdResetEvent2KHR.txt[]
--
endif::VK_KHR_synchronization2[]

[open,refpage='vkCmdResetEvent',desc='Reset an event object to non-signaled state',type='protos']
--
:refpage: vkCmdResetEvent

To set the state of an event to unsignaled from a device, call:

include::{generated}/api/protos/vkCmdResetEvent.txt[]

  * pname:commandBuffer is the command buffer into which the command is
    recorded.
  * pname:event is the event that will be unsignaled.
  * pname:stageMask is a bitmask of elink:VkPipelineStageFlagBits specifying
    the <<synchronization-pipeline-stages, source stage mask>> used to
    determine when the pname:event is unsignaled.

ifdef::VK_KHR_synchronization2[]
fname:vkCmdResetEvent behaves identically to flink:vkCmdResetEvent2KHR.
endif::VK_KHR_synchronization2[]

ifndef::VK_KHR_synchronization2[]
When flink:vkCmdResetEvent is submitted to a queue, it defines an execution
dependency on commands that were submitted before it, and defines an event
unsignal operation which resets the event to the unsignaled state.

The first <<synchronization-dependencies-scopes, synchronization scope>>
includes all commands that occur earlier in
<<synchronization-submission-order,submission order>>.
The synchronization scope is limited to operations on the pipeline stages
determined by the <<synchronization-pipeline-stages-masks, source stage
mask>> specified by pname:stageMask.

The second <<synchronization-dependencies-scopes, synchronization scope>>
includes only the event unsignal operation.

If pname:event is already in the unsignaled state when flink:vkCmdResetEvent
is executed on the device, then flink:vkCmdResetEvent has no effect, no
event unsignal operation occurs, and no execution dependency is generated.
endif::VK_KHR_synchronization2[]

.Valid Usage
****
:stageMaskName: stageMask
include::{chapters}/commonvalidity/stage_mask_common.txt[]
  * [[VUID-vkCmdResetEvent-stageMask-06458]]
    Any pipeline stage included in pname:stageMask must: be supported by the
    capabilities of the queue family specified by the pname:queueFamilyIndex
    member of the slink:VkCommandPoolCreateInfo structure that was used to
    create the sname:VkCommandPool that pname:commandBuffer was allocated
    from, as specified in the <<synchronization-pipeline-stages-supported,
    table of supported pipeline stages>>
  * [[VUID-vkCmdResetEvent-stageMask-01153]]
    pname:stageMask must: not include ename:VK_PIPELINE_STAGE_HOST_BIT
  * [[VUID-vkCmdResetEvent-event-03834]]
    There must: be an execution dependency between fname:vkCmdResetEvent and
    the execution of any flink:vkCmdWaitEvents that includes pname:event in
    its pname:pEvents parameter
ifdef::VK_KHR_synchronization2[]
  * [[VUID-vkCmdResetEvent-event-03835]]
    There must: be an execution dependency between fname:vkCmdResetEvent and
    the execution of any flink:vkCmdWaitEvents2KHR that includes pname:event
    in its pname:pEvents parameter
endif::VK_KHR_synchronization2[]
ifdef::VK_VERSION_1_1,VK_KHR_device_group[]
  * [[VUID-vkCmdResetEvent-commandBuffer-01157]]
    pname:commandBuffer's current device mask must: include exactly one
    physical device
endif::VK_VERSION_1_1,VK_KHR_device_group[]
****

include::{generated}/validity/protos/vkCmdResetEvent.txt[]
--

ifdef::VK_KHR_synchronization2[]
[open,refpage='vkCmdWaitEvents2KHR',desc='Wait for one or more events',type='protos']
--
To wait for one or more events to enter the signaled state on a device,
call:

[[synchronization-events-waiting-device]]
include::{generated}/api/protos/vkCmdWaitEvents2KHR.txt[]

  * pname:commandBuffer is the command buffer into which the command is
    recorded.
  * pname:eventCount is the length of the pname:pEvents array.
  * pname:pEvents is a pointer to an array of pname:eventCount events to
    wait on.
  * pname:pDependencyInfos is a pointer to an array of pname:eventCount
    slink:VkDependencyInfoKHR structures, defining the second
    <<synchronization-dependencies-scopes, synchronization scope>>.

When fname:vkCmdWaitEvents2KHR is submitted to a queue, it inserts memory
dependencies according to the elements of pname:pDependencyInfos and each
corresponding element of pname:pEvents.
fname:vkCmdWaitEvents2KHR must: not be used to wait on event signal
operations occurring on other queues, or signal operations execyted by
flink:vkCmdSetEvent.

The first <<synchronization-dependencies-scopes, synchronization scope>> and
<<synchronization-dependencies-access-scopes, access scope>> of each memory
dependency defined by any element [eq]#i# of pname:pDependencyInfos are
applied to operations that occurred earlier in
<<synchronization-submission-order,submission order>> than the last event
signal operation on element [eq]#i# of pname:pEvents.

Signal operations for an event at index [eq]#i# are only included if:

  * The event was signaled by a flink:vkCmdSetEvent2KHR command that
    occurred earlier in <<synchronization-submission-order,submission
    order>> with a pname:dependencyInfo parameter exactly equal to the
    element of pname:pDependencyInfos at index [eq]#i# ; or
  * The event was created without ename:VK_EVENT_CREATE_DEVICE_ONLY_BIT_KHR,
    and the first <<synchronization-dependencies-scopes, synchronization
    scope>> defined by the element of pname:pDependencyInfos at index
    [eq]#i# only includes host operations
    (ename:VK_PIPELINE_STAGE_2_HOST_BIT_KHR).

The second <<synchronization-dependencies-scopes, synchronization scope>>
and <<synchronization-dependencies-access-scopes, access scope>> of each
memory dependency defined by any element [eq]#i# of pname:pDependencyInfos
are applied to operations that occurred later in
<<synchronization-submission-order,submission order>> than
fname:vkCmdWaitEvents2KHR.

[NOTE]
.Note
====
flink:vkCmdWaitEvents2KHR is used with flink:vkCmdSetEvent2KHR to define a
memory dependency between two sets of action commands, roughly in the same
way as pipeline barriers, but split into two commands such that work between
the two may: execute unhindered.
====

[NOTE]
.Note
====
Applications should be careful to avoid race conditions when using events.
There is no direct ordering guarantee between fname:vkCmdSetEvent2KHR and
flink:vkCmdResetEvent2KHR, flink:vkCmdResetEvent, or flink:vkCmdSetEvent.
Another execution dependency (e.g. a pipeline barrier or semaphore with
ename:VK_PIPELINE_STAGE_2_ALL_COMMANDS_BIT_KHR) is needed to prevent such a
race condition.
====

.Valid Usage
****
  * [[VUID-vkCmdWaitEvents2KHR-synchronization2-03836]]
    The <<features-synchronization2, pname:synchronization2>> feature must:
    be enabled
  * [[VUID-vkCmdWaitEvents2KHR-pEvents-03837]]
    Members of pname:pEvents must: not have been signaled by
    flink:vkCmdSetEvent
  * [[VUID-vkCmdWaitEvents2KHR-pEvents-03838]]
    For any element [eq]#i# of pname:pEvents, if that event is signaled by
    flink:vkCmdSetEvent2KHR, that command's pname:dependencyInfo parameter
    must: be exactly equal to the [eq]##i##th element of
    pname:pDependencyInfos
  * [[VUID-vkCmdWaitEvents2KHR-pEvents-03839]]
    For any element [eq]#i# of pname:pEvents, if that event is signaled by
    flink:vkSetEvent, barriers in the [eq]##i##th element of
    pname:pDependencyInfos must: include only host operations in their first
    <<synchronization-dependencies-scopes, synchronization scope>>
  * [[VUID-vkCmdWaitEvents2KHR-pEvents-03840]]
    For any element [eq]#i# of pname:pEvents, if barriers in the [eq]##i##th
    element of pname:pDependencyInfos include only host operations, the
    [eq]##i##th element of pname:pEvents must: be signaled before
    flink:vkCmdWaitEvents2KHR is executed
  * [[VUID-vkCmdWaitEvents2KHR-pEvents-03841]]
    For any element [eq]#i# of pname:pEvents, if barriers in the [eq]##i##th
    element of pname:pDependencyInfos do not include host operations, the
    [eq]##i##th element of pname:pEvents must: be signaled by a
    corresponding flink:vkCmdSetEvent2KHR that occurred earlier in
    <<synchronization-submission-order,submission order>>
  * [[VUID-vkCmdWaitEvents2KHR-srcStageMask-03842]]
    The pname:srcStageMask member of any element of the
    pname:pMemoryBarriers, pname:pBufferMemoryBarriers, or
    pname:pImageMemoryBarriers members of pname:pDependencyInfos must:
    either include only pipeline stages valid for the queue family that was
    used to create the command pool that pname:commandBuffer was allocated
    from, or include only ename:VK_PIPELINE_STAGE_2_HOST_BIT_KHR
  * [[VUID-vkCmdWaitEvents2KHR-dstStageMask-03843]]
    The pname:dstStageMask member of any element of the
    pname:pMemoryBarriers, pname:pBufferMemoryBarriers, or
    pname:pImageMemoryBarriers members of pname:pDependencyInfos must: only
    include pipeline stages valid for the queue family that was used to
    create the command pool that pname:commandBuffer was allocated from
  * [[VUID-vkCmdWaitEvents2KHR-dependencyFlags-03844]]
    The pname:dependencyFlags member of any element of pname:pDependencyInfo
    must: be `0`
  * [[VUID-vkCmdWaitEvents2KHR-pEvents-03845]]
    If pname:pEvents includes one or more events that will be signaled by
    flink:vkSetEvent after pname:commandBuffer has been submitted to a
    queue, then fname:vkCmdWaitEvents2KHR must: not be called inside a
    render pass instance
  * [[VUID-vkCmdWaitEvents2KHR-commandBuffer-03846]]
    pname:commandBuffer's current device mask must: include exactly one
    physical device
****

include::{generated}/validity/protos/vkCmdWaitEvents2KHR.txt[]
--
endif::VK_KHR_synchronization2[]

[open,refpage='vkCmdWaitEvents',desc='Wait for one or more events and insert a set of memory',type='protos']
--
:refpage: vkCmdWaitEvents

To wait for one or more events to enter the signaled state on a device,
call:

[[synchronization-events-waiting-device]]
include::{generated}/api/protos/vkCmdWaitEvents.txt[]

  * pname:commandBuffer is the command buffer into which the command is
    recorded.
  * pname:eventCount is the length of the pname:pEvents array.
  * pname:pEvents is a pointer to an array of event object handles to wait
    on.
  * pname:srcStageMask is a bitmask of elink:VkPipelineStageFlagBits
    specifying the <<synchronization-pipeline-stages, source stage mask>>.
  * pname:dstStageMask is a bitmask of elink:VkPipelineStageFlagBits
    specifying the <<synchronization-pipeline-stages, destination stage
    mask>>.
  * pname:memoryBarrierCount is the length of the pname:pMemoryBarriers
    array.
  * pname:pMemoryBarriers is a pointer to an array of slink:VkMemoryBarrier
    structures.
  * pname:bufferMemoryBarrierCount is the length of the
    pname:pBufferMemoryBarriers array.
  * pname:pBufferMemoryBarriers is a pointer to an array of
    slink:VkBufferMemoryBarrier structures.
  * pname:imageMemoryBarrierCount is the length of the
    pname:pImageMemoryBarriers array.
  * pname:pImageMemoryBarriers is a pointer to an array of
    slink:VkImageMemoryBarrier structures.

ifdef::VK_KHR_synchronization2[]
fname:vkCmdWaitEvents is largely similar to flink:vkCmdWaitEvents2KHR, but
can: only wait on signal operations defined by flink:vkCmdSetEvent.
As flink:vkCmdSetEvent does not define any access scopes,
fname:vkCmdWaitEvents defines the first access scope for each event signal
operation in addition to its own access scopes.

[NOTE]
.Note
====
Since flink:vkCmdSetEvent does not have any dependency information beyond a
stage mask, implementations do not have the same opportunity to perform
<<synchronization-dependencies-available-and-visible, availability and
visibility operations>> or <<synchronization-image-layout-transitions, image
layout transitions>> in advance as they do with flink:vkCmdSetEvent2KHR and
flink:vkCmdWaitEvents2KHR.
====
endif::VK_KHR_synchronization2[]

When fname:vkCmdWaitEvents is submitted to a queue, it defines a memory
dependency between prior event signal operations on the same queue or the
host, and subsequent commands.
fname:vkCmdWaitEvents must: not be used to wait on event signal operations
occurring on other queues.

The first synchronization scope only includes event signal operations that
operate on members of pname:pEvents, and the operations that happened-before
the event signal operations.
Event signal operations performed by flink:vkCmdSetEvent that occur earlier
in <<synchronization-submission-order,submission order>> are included in the
first synchronization scope, if the <<synchronization-pipeline-stages-order,
logically latest>> pipeline stage in their pname:stageMask parameter is
<<synchronization-pipeline-stages-order, logically earlier>> than or equal
to the <<synchronization-pipeline-stages-order, logically latest>> pipeline
stage in pname:srcStageMask.
Event signal operations performed by flink:vkSetEvent are only included in
the first synchronization scope if ename:VK_PIPELINE_STAGE_HOST_BIT is
included in pname:srcStageMask.

The second <<synchronization-dependencies-scopes, synchronization scope>>
includes all commands that occur later in
<<synchronization-submission-order,submission order>>.
The second synchronization scope is limited to operations on the pipeline
stages determined by the <<synchronization-pipeline-stages-masks,
destination stage mask>> specified by pname:dstStageMask.

The first <<synchronization-dependencies-access-scopes, access scope>> is
limited to accesses in the pipeline stages determined by the
<<synchronization-pipeline-stages-masks, source stage mask>> specified by
pname:srcStageMask.
Within that, the first access scope only includes the first access scopes
defined by elements of the pname:pMemoryBarriers,
pname:pBufferMemoryBarriers and pname:pImageMemoryBarriers arrays, which
each define a set of <<synchronization-memory-barriers, memory barriers>>.
If no memory barriers are specified, then the first access scope includes no
accesses.

The second <<synchronization-dependencies-access-scopes, access scope>> is
limited to accesses in the pipeline stages determined by the
<<synchronization-pipeline-stages-masks, destination stage mask>> specified
by pname:dstStageMask.
Within that, the second access scope only includes the second access scopes
defined by elements of the pname:pMemoryBarriers,
pname:pBufferMemoryBarriers and pname:pImageMemoryBarriers arrays, which
each define a set of <<synchronization-memory-barriers, memory barriers>>.
If no memory barriers are specified, then the second access scope includes
no accesses.

ifndef::VK_KHR_synchronization2[]
[NOTE]
.Note
====
flink:vkCmdWaitEvents is used with flink:vkCmdSetEvent to define a memory
dependency between two sets of action commands, roughly in the same way as
pipeline barriers, but split into two commands such that work between the
two may: execute unhindered.

Unlike flink:vkCmdPipelineBarrier, a <<synchronization-queue-transfers,
queue family ownership transfer>> cannot: be performed using
flink:vkCmdWaitEvents.
====

[NOTE]
.Note
====
Applications should be careful to avoid race conditions when using events.
There is no direct ordering guarantee between flink:vkCmdWaitEvents and
ifdef::VK_KHR_synchronization2[flink:vkCmdResetEvent2KHR,]
flink:vkCmdResetEvent, or flink:vkCmdSetEvent.
Another execution dependency (e.g. a pipeline barrier or semaphore with
ename:VK_PIPELINE_STAGE_ALL_COMMANDS_BIT) is needed to prevent such a race
condition.
====
endif::VK_KHR_synchronization2[]

.Valid Usage
****
:stageMaskName: srcStageMask
include::{chapters}/commonvalidity/stage_mask_common.txt[]

:stageMaskName: dstStageMask
include::{chapters}/commonvalidity/stage_mask_common.txt[]
include::{chapters}/commonvalidity/fine_sync_commands_common.txt[]
  * [[VUID-vkCmdWaitEvents-srcStageMask-06459]]
    Any pipeline stage included in pname:srcStageMask must: be supported by
    the capabilities of the queue family specified by the
    pname:queueFamilyIndex member of the slink:VkCommandPoolCreateInfo
    structure that was used to create the sname:VkCommandPool that
    pname:commandBuffer was allocated from, as specified in the
    <<synchronization-pipeline-stages-supported, table of supported pipeline
    stages>>
  * [[VUID-vkCmdWaitEvents-dstStageMask-06460]]
    Any pipeline stage included in pname:dstStageMask must: be supported by
    the capabilities of the queue family specified by the
    pname:queueFamilyIndex member of the slink:VkCommandPoolCreateInfo
    structure that was used to create the sname:VkCommandPool that
    pname:commandBuffer was allocated from, as specified in the
    <<synchronization-pipeline-stages-supported, table of supported pipeline
    stages>>
  * [[VUID-vkCmdWaitEvents-srcStageMask-01158]]
    pname:srcStageMask must: be the bitwise OR of the pname:stageMask
    parameter used in previous calls to fname:vkCmdSetEvent with any of the
    elements of pname:pEvents and ename:VK_PIPELINE_STAGE_HOST_BIT if any of
    the elements of pname:pEvents was set using fname:vkSetEvent
  * [[VUID-vkCmdWaitEvents-pEvents-01163]]
    If pname:pEvents includes one or more events that will be signaled by
    fname:vkSetEvent after pname:commandBuffer has been submitted to a
    queue, then fname:vkCmdWaitEvents must: not be called inside a render
    pass instance
  * [[VUID-vkCmdWaitEvents-srcQueueFamilyIndex-02803]]
    The pname:srcQueueFamilyIndex and pname:dstQueueFamilyIndex members of
    any element of pname:pBufferMemoryBarriers or pname:pImageMemoryBarriers
    must: be equal
ifdef::VK_VERSION_1_1,VK_KHR_device_group[]
  * [[VUID-vkCmdWaitEvents-commandBuffer-01167]]
    pname:commandBuffer's current device mask must: include exactly one
    physical device
endif::VK_VERSION_1_1,VK_KHR_device_group[]
ifdef::VK_KHR_synchronization2[]
  * [[VUID-vkCmdWaitEvents-pEvents-03847]]
    Elements of pname:pEvents must: not have been signaled by
    flink:vkCmdSetEvent2KHR
endif::VK_KHR_synchronization2[]
****

include::{generated}/validity/protos/vkCmdWaitEvents.txt[]
--


[[synchronization-pipeline-barriers]]
== Pipeline Barriers

ifdef::VK_KHR_synchronization2[]
[open,refpage='vkCmdPipelineBarrier2KHR',desc='Insert a memory dependency',type='protos']
--
:refpage: vkCmdPipelineBarrier2KHR

To record a pipeline barrier, call:

include::{generated}/api/protos/vkCmdPipelineBarrier2KHR.txt[]

  * pname:commandBuffer is the command buffer into which the command is
    recorded.
  * pname:pDependencyInfo is a pointer to a slink:VkDependencyInfoKHR
    structure defining the scopes of this operation.

When flink:vkCmdPipelineBarrier2KHR is submitted to a queue, it defines
memory dependencies between commands that were submitted before it, and
those submitted after it.

The first <<synchronization-dependencies-scopes, synchronization scope>> and
<<synchronization-dependencies-access-scopes, access scope>> of each memory
dependency defined by pname:pDependencyInfo are applied to operations that
occurred earlier in <<synchronization-submission-order,submission order>>.

The second <<synchronization-dependencies-scopes, synchronization scope>>
and <<synchronization-dependencies-access-scopes, access scope>> of each
memory dependency defined by pname:pDependencyInfo are applied to operations
that occurred later in <<synchronization-submission-order,submission
order>>.

If fname:vkCmdPipelineBarrier2KHR is recorded within a render pass instance,
the synchronization scopes are
<<synchronization-pipeline-barriers-subpass-self-dependencies, limited to
operations within the same subpass>>.

.Valid Usage
****
include::{chapters}/commonvalidity/pipeline_barrier_common.txt[]
  * [[VUID-vkCmdPipelineBarrier2KHR-synchronization2-03848]]
    The <<features-synchronization2, pname:synchronization2>> feature must:
    be enabled
  * [[VUID-vkCmdPipelineBarrier2KHR-srcStageMask-03849]]
    The pname:srcStageMask member of any element of the
    pname:pMemoryBarriers, pname:pBufferMemoryBarriers, or
    pname:pImageMemoryBarriers members of pname:pDependencyInfo must: only
    include pipeline stages valid for the queue family that was used to
    create the command pool that pname:commandBuffer was allocated from
  * [[VUID-vkCmdPipelineBarrier2KHR-dstStageMask-03850]]
    The pname:dstStageMask member of any element of the
    pname:pMemoryBarriers, pname:pBufferMemoryBarriers, or
    pname:pImageMemoryBarriers members of pname:pDependencyInfo must: only
    include pipeline stages valid for the queue family that was used to
    create the command pool that pname:commandBuffer was allocated from
****

include::{generated}/validity/protos/vkCmdPipelineBarrier2KHR.txt[]
--
endif::VK_KHR_synchronization2[]

[open,refpage='vkCmdPipelineBarrier',desc='Insert a memory dependency',type='protos']
--
:refpage: vkCmdPipelineBarrier

To record a pipeline barrier, call:

include::{generated}/api/protos/vkCmdPipelineBarrier.txt[]

  * pname:commandBuffer is the command buffer into which the command is
    recorded.
  * pname:srcStageMask is a bitmask of elink:VkPipelineStageFlagBits
    specifying the <<synchronization-pipeline-stages-masks,source stages>>.
  * pname:dstStageMask is a bitmask of elink:VkPipelineStageFlagBits
    specifying the <<synchronization-pipeline-stages-masks,destination
    stages>>.
  * pname:dependencyFlags is a bitmask of elink:VkDependencyFlagBits
    specifying how execution and memory dependencies are formed.
  * pname:memoryBarrierCount is the length of the pname:pMemoryBarriers
    array.
  * pname:pMemoryBarriers is a pointer to an array of slink:VkMemoryBarrier
    structures.
  * pname:bufferMemoryBarrierCount is the length of the
    pname:pBufferMemoryBarriers array.
  * pname:pBufferMemoryBarriers is a pointer to an array of
    slink:VkBufferMemoryBarrier structures.
  * pname:imageMemoryBarrierCount is the length of the
    pname:pImageMemoryBarriers array.
  * pname:pImageMemoryBarriers is a pointer to an array of
    slink:VkImageMemoryBarrier structures.

ifdef::VK_KHR_synchronization2[]
fname:vkCmdPipelineBarrier operates almost identically to
flink:vkCmdPipelineBarrier2KHR, except that the scopes and barriers are
defined as direct parameters rather than being defined by an
slink:VkDependencyInfoKHR.
endif::VK_KHR_synchronization2[]

When flink:vkCmdPipelineBarrier is submitted to a queue, it defines a memory
dependency between commands that were submitted before it, and those
submitted after it.

If flink:vkCmdPipelineBarrier was recorded outside a render pass instance,
the first <<synchronization-dependencies-scopes, synchronization scope>>
includes all commands that occur earlier in
<<synchronization-submission-order,submission order>>.
If flink:vkCmdPipelineBarrier was recorded inside a render pass instance,
the first synchronization scope includes only commands that occur earlier in
<<synchronization-submission-order,submission order>> within the same
subpass.
In either case, the first synchronization scope is limited to operations on
the pipeline stages determined by the
<<synchronization-pipeline-stages-masks, source stage mask>> specified by
pname:srcStageMask.

If flink:vkCmdPipelineBarrier was recorded outside a render pass instance,
the second <<synchronization-dependencies-scopes, synchronization scope>>
includes all commands that occur later in
<<synchronization-submission-order,submission order>>.
If flink:vkCmdPipelineBarrier was recorded inside a render pass instance,
the second synchronization scope includes only commands that occur later in
<<synchronization-submission-order,submission order>> within the same
subpass.
In either case, the second synchronization scope is limited to operations on
the pipeline stages determined by the
<<synchronization-pipeline-stages-masks, destination stage mask>> specified
by pname:dstStageMask.

The first <<synchronization-dependencies-access-scopes, access scope>> is
limited to accesses in the pipeline stages determined by the
<<synchronization-pipeline-stages-masks, source stage mask>> specified by
pname:srcStageMask.
Within that, the first access scope only includes the first access scopes
defined by elements of the pname:pMemoryBarriers,
pname:pBufferMemoryBarriers and pname:pImageMemoryBarriers arrays, which
each define a set of <<synchronization-memory-barriers, memory barriers>>.
If no memory barriers are specified, then the first access scope includes no
accesses.

The second <<synchronization-dependencies-access-scopes, access scope>> is
limited to accesses in the pipeline stages determined by the
<<synchronization-pipeline-stages-masks, destination stage mask>> specified
by pname:dstStageMask.
Within that, the second access scope only includes the second access scopes
defined by elements of the pname:pMemoryBarriers,
pname:pBufferMemoryBarriers and pname:pImageMemoryBarriers arrays, which
each define a set of <<synchronization-memory-barriers, memory barriers>>.
If no memory barriers are specified, then the second access scope includes
no accesses.

If pname:dependencyFlags includes ename:VK_DEPENDENCY_BY_REGION_BIT, then
any dependency between <<synchronization-framebuffer-regions,
framebuffer-space>> pipeline stages is
<<synchronization-framebuffer-regions, framebuffer-local>> - otherwise it is
<<synchronization-framebuffer-regions, framebuffer-global>>.

.Valid Usage
****
:stageMaskName: srcStageMask
include::{chapters}/commonvalidity/stage_mask_common.txt[]

:stageMaskName: dstStageMask
include::{chapters}/commonvalidity/stage_mask_common.txt[]
include::{chapters}/commonvalidity/fine_sync_commands_common.txt[]
include::{chapters}/commonvalidity/pipeline_barrier_common.txt[]
  * [[VUID-vkCmdPipelineBarrier-srcStageMask-06461]]
    Any pipeline stage included in pname:srcStageMask must: be supported by
    the capabilities of the queue family specified by the
    pname:queueFamilyIndex member of the slink:VkCommandPoolCreateInfo
    structure that was used to create the sname:VkCommandPool that
    pname:commandBuffer was allocated from, as specified in the
    <<synchronization-pipeline-stages-supported, table of supported pipeline
    stages>>
  * [[VUID-vkCmdPipelineBarrier-dstStageMask-06462]]
    Any pipeline stage included in pname:dstStageMask must: be supported by
    the capabilities of the queue family specified by the
    pname:queueFamilyIndex member of the slink:VkCommandPoolCreateInfo
    structure that was used to create the sname:VkCommandPool that
    pname:commandBuffer was allocated from, as specified in the
    <<synchronization-pipeline-stages-supported, table of supported pipeline
    stages>>
****

include::{generated}/validity/protos/vkCmdPipelineBarrier.txt[]
--

[open,refpage='VkDependencyFlagBits',desc='Bitmask specifying how execution and memory dependencies are formed',type='enums']
--
Bits which can: be set in fname:vkCmdPipelineBarrier::pname:dependencyFlags,
specifying how execution and memory dependencies are formed, are:

include::{generated}/api/enums/VkDependencyFlagBits.txt[]

  * ename:VK_DEPENDENCY_BY_REGION_BIT specifies that dependencies will be
    <<synchronization-framebuffer-regions, framebuffer-local>>.
ifdef::VK_VERSION_1_1,VK_KHR_multiview[]
  * ename:VK_DEPENDENCY_VIEW_LOCAL_BIT specifies that a
    <<synchronization-pipeline-barriers-subpass-self-dependencies, subpass
    has more than one view>>.
endif::VK_VERSION_1_1,VK_KHR_multiview[]
ifdef::VK_VERSION_1_1,VK_KHR_device_group[]
  * ename:VK_DEPENDENCY_DEVICE_GROUP_BIT specifies that dependencies are
    <<synchronization-device-local-dependencies, non-device-local>>.
endif::VK_VERSION_1_1,VK_KHR_device_group[]
--

[open,refpage='VkDependencyFlags',desc='Bitmask of VkDependencyFlagBits',type='flags']
--
include::{generated}/api/flags/VkDependencyFlags.txt[]

tname:VkDependencyFlags is a bitmask type for setting a mask of zero or more
elink:VkDependencyFlagBits.
--


[[synchronization-pipeline-barriers-subpass-self-dependencies]]
=== Subpass Self-dependency

ifdef::VK_KHR_dynamic_rendering[]
flink:vkCmdPipelineBarrier
ifdef::VK_KHR_synchronization2[]
or flink:vkCmdPipelineBarrier2KHR
endif::VK_KHR_synchronization2[]
must: not be called within a render pass instance started with
flink:vkCmdBeginRenderingKHR.
endif::VK_KHR_dynamic_rendering[]

If flink:vkCmdPipelineBarrier
ifdef::VK_KHR_synchronization2[]
or flink:vkCmdPipelineBarrier2KHR
endif::VK_KHR_synchronization2[]
is called inside a render pass instance, the following restrictions apply.
For a given subpass to allow a pipeline barrier, the render pass must:
declare a _self-dependency_ from that subpass to itself.
That is, there must: exist a subpass dependency with pname:srcSubpass and
pname:dstSubpass both equal to that subpass index.
More than one self-dependency can: be declared for each subpass.

Self-dependencies must: only include pipeline stage bits that are graphics
stages.
If any of the stages in pname:srcStageMask are
<<synchronization-framebuffer-regions,framebuffer-space stages>>,
pname:dstStageMask must: only contain
<<synchronization-framebuffer-regions,framebuffer-space stages>>.
This means that pseudo-stages like ename:VK_PIPELINE_STAGE_ALL_COMMANDS_BIT
which include the execution of both framebuffer-space stages and
non-framebuffer-space stages must: not be used.

If the source and destination stage masks both include framebuffer-space
stages, then pname:dependencyFlags must: include
ename:VK_DEPENDENCY_BY_REGION_BIT.
ifdef::VK_VERSION_1_1,VK_KHR_multiview[]
If the subpass has more than one view, then pname:dependencyFlags must:
include ename:VK_DEPENDENCY_VIEW_LOCAL_BIT.
endif::VK_VERSION_1_1,VK_KHR_multiview[]

Each of the <<synchronization-dependencies-scopes, synchronization scopes>>
and <<synchronization-dependencies-access-scopes, access scopes>> of a
ifdef::VK_KHR_synchronization2[]
flink:vkCmdPipelineBarrier2KHR or
endif::VK_KHR_synchronization2[]
flink:vkCmdPipelineBarrier command inside a render pass instance must: be a
subset of the scopes of one of the self-dependencies for the current
subpass.

If the self-dependency has ename:VK_DEPENDENCY_BY_REGION_BIT
ifdef::VK_VERSION_1_1,VK_KHR_multiview[]
or ename:VK_DEPENDENCY_VIEW_LOCAL_BIT
endif::VK_VERSION_1_1,VK_KHR_multiview[]
set, then so must: the pipeline barrier.
Pipeline barriers within a render pass instance must: not include buffer
memory barriers.
Image memory barriers must: only specify image subresources that are used as
attachments within the subpass, and must: not define an
<<synchronization-image-layout-transitions, image layout transition>> or
<<synchronization-queue-transfers, queue family ownership transfer>>.


[[synchronization-memory-barriers]]
== Memory Barriers

_Memory barriers_ are used to explicitly control access to buffer and image
subresource ranges.
Memory barriers are used to <<synchronization-queue-transfers, transfer
ownership between queue families>>,
<<synchronization-image-layout-transitions, change image layouts>>, and
define <<synchronization-dependencies-available-and-visible, availability
and visibility operations>>.
They explicitly define the <<synchronization-access-types, access types>>
and buffer and image subresource ranges that are included in the
<<synchronization-dependencies-access-scopes, access scopes>> of a memory
dependency that is created by a synchronization command that includes them.


[[synchronization-global-memory-barriers]]
=== Global Memory Barriers

Global memory barriers apply to memory accesses involving all memory objects
that exist at the time of its execution.

ifdef::VK_KHR_synchronization2[]
[open,refpage='VkMemoryBarrier2KHR',desc='Structure specifying a global memory barrier',type='structs']
--
:refpage: VkMemoryBarrier2KHR

The sname:VkMemoryBarrier2KHR structure is defined as:

include::{generated}/api/structs/VkMemoryBarrier2KHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:srcStageMask is a tlink:VkPipelineStageFlags2KHR mask of pipeline
    stages to be included in the <<synchronization-dependencies-scopes,
    first synchronization scope>>.
  * pname:srcAccessMask is a tlink:VkAccessFlags2KHR mask of access flags to
    be included in the <<synchronization-dependencies-access-scopes, first
    access scope>>.
  * pname:dstStageMask is a tlink:VkPipelineStageFlags2KHR mask of pipeline
    stages to be included in the <<synchronization-dependencies-scopes,
    second synchronization scope>>.
  * pname:dstAccessMask is a tlink:VkAccessFlags2KHR mask of access flags to
    be included in the <<synchronization-dependencies-access-scopes, second
    access scope>>.

This structure defines a <<synchronization-dependencies-memory, memory
dependency>> affecting all device memory.

The first <<synchronization-dependencies-scopes, synchronization scope>> and
<<synchronization-dependencies-access-scopes, access scope>> described by
this structure include only operations and memory accesses specified by
pname:srcStageMask and pname:srcAccessMask.

The second <<synchronization-dependencies-scopes, synchronization scope>>
and <<synchronization-dependencies-access-scopes, access scope>> described
by this structure include only operations and memory accesses specified by
pname:dstStageMask and pname:dstAccessMask.

.Valid Usage
****
:stageMaskName: srcStageMask
:accessMaskName: srcAccessMask
include::{chapters}/commonvalidity/stage_mask_2_common.txt[]
include::{chapters}/commonvalidity/access_mask_2_common.txt[]

:stageMaskName: dstStageMask
:accessMaskName: dstAccessMask
include::{chapters}/commonvalidity/stage_mask_2_common.txt[]
include::{chapters}/commonvalidity/access_mask_2_common.txt[]
****

include::{generated}/validity/structs/VkMemoryBarrier2KHR.txt[]
--
endif::VK_KHR_synchronization2[]

[open,refpage='VkMemoryBarrier',desc='Structure specifying a global memory barrier',type='structs']
--
The sname:VkMemoryBarrier structure is defined as:

include::{generated}/api/structs/VkMemoryBarrier.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:srcAccessMask is a bitmask of elink:VkAccessFlagBits specifying a
    <<synchronization-access-masks, source access mask>>.
  * pname:dstAccessMask is a bitmask of elink:VkAccessFlagBits specifying a
    <<synchronization-access-masks, destination access mask>>.

The first <<synchronization-dependencies-access-scopes, access scope>> is
limited to access types in the <<synchronization-access-masks, source access
mask>> specified by pname:srcAccessMask.

The second <<synchronization-dependencies-access-scopes, access scope>> is
limited to access types in the <<synchronization-access-masks, destination
access mask>> specified by pname:dstAccessMask.

include::{generated}/validity/structs/VkMemoryBarrier.txt[]
--


[[synchronization-buffer-memory-barriers]]
=== Buffer Memory Barriers

Buffer memory barriers only apply to memory accesses involving a specific
buffer range.
That is, a memory dependency formed from a buffer memory barrier is
<<synchronization-dependencies-access-scopes, scoped>> to access via the
specified buffer range.
Buffer memory barriers can: also be used to define a
<<synchronization-queue-transfers, queue family ownership transfer>> for the
specified buffer range.

ifdef::VK_KHR_synchronization2[]
[open,refpage='VkBufferMemoryBarrier2KHR',desc='Structure specifying a buffer memory barrier',type='structs']
--
:refpage: VkBufferMemoryBarrier2KHR

The sname:VkBufferMemoryBarrier2KHR structure is defined as:

include::{generated}/api/structs/VkBufferMemoryBarrier2KHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:srcStageMask is a tlink:VkPipelineStageFlags2KHR mask of pipeline
    stages to be included in the <<synchronization-dependencies-scopes,
    first synchronization scope>>.
  * pname:srcAccessMask is a tlink:VkAccessFlags2KHR mask of access flags to
    be included in the <<synchronization-dependencies-access-scopes, first
    access scope>>.
  * pname:dstStageMask is a tlink:VkPipelineStageFlags2KHR mask of pipeline
    stages to be included in the <<synchronization-dependencies-scopes,
    second synchronization scope>>.
  * pname:dstAccessMask is a tlink:VkAccessFlags2KHR mask of access flags to
    be included in the <<synchronization-dependencies-access-scopes, second
    access scope>>.
  * pname:srcQueueFamilyIndex is the source queue family for a
    <<synchronization-queue-transfers, queue family ownership transfer>>.
  * pname:dstQueueFamilyIndex is the destination queue family for a
    <<synchronization-queue-transfers, queue family ownership transfer>>.
  * pname:buffer is a handle to the buffer whose backing memory is affected
    by the barrier.
  * pname:offset is an offset in bytes into the backing memory for
    pname:buffer; this is relative to the base offset as bound to the buffer
    (see flink:vkBindBufferMemory).
  * pname:size is a size in bytes of the affected area of backing memory for
    pname:buffer, or ename:VK_WHOLE_SIZE to use the range from pname:offset
    to the end of the buffer.

This structure defines a <<synchronization-dependencies-memory, memory
dependency>> limited to a range of a buffer, and can: define a
<<synchronization-queue-transfers, queue family transfer operation>> for
that range.

The first <<synchronization-dependencies-scopes, synchronization scope>> and
<<synchronization-dependencies-access-scopes, access scope>> described by
this structure include only operations and memory accesses specified by
pname:srcStageMask and pname:srcAccessMask.

The second <<synchronization-dependencies-scopes, synchronization scope>>
and <<synchronization-dependencies-access-scopes, access scope>> described
by this structure include only operations and memory accesses specified by
pname:dstStageMask and pname:dstAccessMask.

Both <<synchronization-dependencies-access-scopes, access scopes>> are
limited to only memory accesses to pname:buffer in the range defined by
pname:offset and pname:size.

If pname:buffer was created with ename:VK_SHARING_MODE_EXCLUSIVE, and
pname:srcQueueFamilyIndex is not equal to pname:dstQueueFamilyIndex, this
memory barrier defines a <<synchronization-queue-transfers, queue family
transfer operation>>.
When executed on a queue in the family identified by
pname:srcQueueFamilyIndex, this barrier defines a
<<synchronization-queue-transfers-release, queue family release operation>>
for the specified buffer range, and the second synchronization and access
scopes do not synchronize operations on that queue.
When executed on a queue in the family identified by
pname:dstQueueFamilyIndex, this barrier defines a
<<synchronization-queue-transfers-acquire, queue family acquire operation>>
for the specified buffer range, and the first synchronization and access
scopes do not synchronize operations on that queue.

ifdef::VK_VERSION_1_1,VK_KHR_external_memory[]
A <<synchronization-queue-transfers, queue family transfer operation>> is
also defined if the values are not equal, and either is one of the special
queue family values reserved for external memory ownership transfers, as
described in <<synchronization-queue-transfers>>.
A <<synchronization-queue-transfers-release, queue family release
operation>> is defined when pname:dstQueueFamilyIndex is one of those
values, and a <<synchronization-queue-transfers-acquire, queue family
acquire operation>> is defined when pname:srcQueueFamilyIndex is one of
those values.
endif::VK_VERSION_1_1,VK_KHR_external_memory[]


.Valid Usage
****

:stageMaskName: srcStageMask
:accessMaskName: srcAccessMask
include::{chapters}/commonvalidity/stage_mask_2_common.txt[]
include::{chapters}/commonvalidity/access_mask_2_common.txt[]

:stageMaskName: dstStageMask
:accessMaskName: dstAccessMask
include::{chapters}/commonvalidity/stage_mask_2_common.txt[]
include::{chapters}/commonvalidity/access_mask_2_common.txt[]
include::{chapters}/commonvalidity/buffer_memory_barrier_common.txt[]
  * [[VUID-VkBufferMemoryBarrier2KHR-srcStageMask-03851]]
    If either pname:srcStageMask or pname:dstStageMask includes
    ename:VK_PIPELINE_STAGE_2_HOST_BIT_KHR, pname:srcQueueFamilyIndex and
    pname:dstQueueFamilyIndex must: be equal
****

include::{generated}/validity/structs/VkBufferMemoryBarrier2KHR.txt[]
--
endif::VK_KHR_synchronization2[]

[open,refpage='VkBufferMemoryBarrier',desc='Structure specifying a buffer memory barrier',type='structs']
--
:refpage: VkBufferMemoryBarrier

The sname:VkBufferMemoryBarrier structure is defined as:

include::{generated}/api/structs/VkBufferMemoryBarrier.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:srcAccessMask is a bitmask of elink:VkAccessFlagBits specifying a
    <<synchronization-access-masks, source access mask>>.
  * pname:dstAccessMask is a bitmask of elink:VkAccessFlagBits specifying a
    <<synchronization-access-masks, destination access mask>>.
  * pname:srcQueueFamilyIndex is the source queue family for a
    <<synchronization-queue-transfers, queue family ownership transfer>>.
  * pname:dstQueueFamilyIndex is the destination queue family for a
    <<synchronization-queue-transfers, queue family ownership transfer>>.
  * pname:buffer is a handle to the buffer whose backing memory is affected
    by the barrier.
  * pname:offset is an offset in bytes into the backing memory for
    pname:buffer; this is relative to the base offset as bound to the buffer
    (see flink:vkBindBufferMemory).
  * pname:size is a size in bytes of the affected area of backing memory for
    pname:buffer, or ename:VK_WHOLE_SIZE to use the range from pname:offset
    to the end of the buffer.

The first <<synchronization-dependencies-access-scopes, access scope>> is
limited to access to memory through the specified buffer range, via access
types in the <<synchronization-access-masks, source access mask>> specified
by pname:srcAccessMask.
If pname:srcAccessMask includes ename:VK_ACCESS_HOST_WRITE_BIT, memory
writes performed by that access type are also made visible, as that access
type is not performed through a resource.

The second <<synchronization-dependencies-access-scopes, access scope>> is
limited to access to memory through the specified buffer range, via access
types in the <<synchronization-access-masks, destination access mask>>
specified by pname:dstAccessMask.
If pname:dstAccessMask includes ename:VK_ACCESS_HOST_WRITE_BIT or
ename:VK_ACCESS_HOST_READ_BIT, available memory writes are also made visible
to accesses of those types, as those access types are not performed through
a resource.

If pname:srcQueueFamilyIndex is not equal to pname:dstQueueFamilyIndex, and
pname:srcQueueFamilyIndex is equal to the current queue family, then the
memory barrier defines a <<synchronization-queue-transfers-release, queue
family release operation>> for the specified buffer range, and the second
access scope includes no access, as if pname:dstAccessMask was `0`.

If pname:dstQueueFamilyIndex is not equal to pname:srcQueueFamilyIndex, and
pname:dstQueueFamilyIndex is equal to the current queue family, then the
memory barrier defines a <<synchronization-queue-transfers-acquire, queue
family acquire operation>> for the specified buffer range, and the first
access scope includes no access, as if pname:srcAccessMask was `0`.

.Valid Usage
****
include::{chapters}/commonvalidity/buffer_memory_barrier_common.txt[]
ifndef::VK_VERSION_1_1,VK_KHR_external_memory[]
  * [[VUID-VkBufferMemoryBarrier-synchronization2-03852]]
    If the <<features-synchronization2,pname:synchronization2 feature>> is
    not enabled, and pname:buffer was created with a sharing mode of
    ename:VK_SHARING_MODE_CONCURRENT, pname:srcQueueFamilyIndex and
    pname:dstQueueFamilyIndex must: both be ename:VK_QUEUE_FAMILY_IGNORED
endif::VK_VERSION_1_1,VK_KHR_external_memory[]
ifdef::VK_VERSION_1_1,VK_KHR_external_memory[]
  * [[VUID-VkBufferMemoryBarrier-synchronization2-03853]]
    If the <<features-synchronization2,pname:synchronization2 feature>> is
    not enabled, and pname:buffer was created with a sharing mode of
    ename:VK_SHARING_MODE_CONCURRENT, at least one of
    pname:srcQueueFamilyIndex and pname:dstQueueFamilyIndex must: be
    ename:VK_QUEUE_FAMILY_IGNORED
endif::VK_VERSION_1_1,VK_KHR_external_memory[]
****

include::{generated}/validity/structs/VkBufferMemoryBarrier.txt[]
--

[open,refpage='VK_WHOLE_SIZE',desc='Sentinel value to use entire remaining array length',type='consts']
--
ename:VK_WHOLE_SIZE is a special value indicating that the entire remaining
length of a buffer following a given pname:offset should be used.
It can: be specified for slink:VkBufferMemoryBarrier::pname:size and other
structures.

include::{generated}/api/enums/VK_WHOLE_SIZE.txt[]
--


[[synchronization-image-memory-barriers]]
=== Image Memory Barriers

Image memory barriers only apply to memory accesses involving a specific
image subresource range.
That is, a memory dependency formed from an image memory barrier is
<<synchronization-dependencies-access-scopes, scoped>> to access via the
specified image subresource range.
Image memory barriers can: also be used to define
<<synchronization-image-layout-transitions, image layout transitions>> or a
<<synchronization-queue-transfers, queue family ownership transfer>> for the
specified image subresource range.

ifdef::VK_KHR_synchronization2[]
[open,refpage='VkImageMemoryBarrier2KHR',desc='Structure specifying an image memory barrier',type='structs']
--
:refpage: VkImageMemoryBarrier2KHR

The sname:VkImageMemoryBarrier2KHR structure is defined as:

include::{generated}/api/structs/VkImageMemoryBarrier2KHR.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:srcStageMask is a tlink:VkPipelineStageFlags2KHR mask of pipeline
    stages to be included in the <<synchronization-dependencies-scopes,
    first synchronization scope>>.
  * pname:srcAccessMask is a tlink:VkAccessFlags2KHR mask of access flags to
    be included in the <<synchronization-dependencies-access-scopes, first
    access scope>>.
  * pname:dstStageMask is a tlink:VkPipelineStageFlags2KHR mask of pipeline
    stages to be included in the <<synchronization-dependencies-scopes,
    second synchronization scope>>.
  * pname:dstAccessMask is a tlink:VkAccessFlags2KHR mask of access flags to
    be included in the <<synchronization-dependencies-access-scopes, second
    access scope>>.
  * pname:oldLayout is the old layout in an
    <<synchronization-image-layout-transitions, image layout transition>>.
  * pname:newLayout is the new layout in an
    <<synchronization-image-layout-transitions, image layout transition>>.
  * pname:srcQueueFamilyIndex is the source queue family for a
    <<synchronization-queue-transfers, queue family ownership transfer>>.
  * pname:dstQueueFamilyIndex is the destination queue family for a
    <<synchronization-queue-transfers, queue family ownership transfer>>.
  * pname:image is a handle to the image affected by this barrier.
  * pname:subresourceRange describes the <<resources-image-views, image
    subresource range>> within pname:image that is affected by this barrier.

This structure defines a <<synchronization-dependencies-memory, memory
dependency>> limited to an image subresource range, and can: define a
<<synchronization-queue-transfers, queue family transfer operation>> and
<<synchronization-image-layout-transitions, image layout transition>> for
that subresource range.

The first <<synchronization-dependencies-scopes, synchronization scope>> and
<<synchronization-dependencies-access-scopes, access scope>> described by
this structure include only operations and memory accesses specified by
pname:srcStageMask and pname:srcAccessMask.

The second <<synchronization-dependencies-scopes, synchronization scope>>
and <<synchronization-dependencies-access-scopes, access scope>> described
by this structure include only operations and memory accesses specified by
pname:dstStageMask and pname:dstAccessMask.

Both <<synchronization-dependencies-access-scopes, access scopes>> are
limited to only memory accesses to pname:image in the subresource range
defined by pname:subresourceRange.

If pname:image was created with ename:VK_SHARING_MODE_EXCLUSIVE, and
pname:srcQueueFamilyIndex is not equal to pname:dstQueueFamilyIndex, this
memory barrier defines a <<synchronization-queue-transfers, queue family
transfer operation>>.
When executed on a queue in the family identified by
pname:srcQueueFamilyIndex, this barrier defines a
<<synchronization-queue-transfers-release, queue family release operation>>
for the specified image subresource range, and the second synchronization
and access scopes do not synchronize operations on that queue.
When executed on a queue in the family identified by
pname:dstQueueFamilyIndex, this barrier defines a
<<synchronization-queue-transfers-acquire, queue family acquire operation>>
for the specified image subresource range, and the first synchronization and
access scopes do not synchronize operations on that queue.

ifdef::VK_VERSION_1_1,VK_KHR_external_memory[]
A <<synchronization-queue-transfers, queue family transfer operation>> is
also defined if the values are not equal, and either is one of the special
queue family values reserved for external memory ownership transfers, as
described in <<synchronization-queue-transfers>>.
A <<synchronization-queue-transfers-release, queue family release
operation>> is defined when pname:dstQueueFamilyIndex is one of those
values, and a <<synchronization-queue-transfers-acquire, queue family
acquire operation>> is defined when pname:srcQueueFamilyIndex is one of
those values.
endif::VK_VERSION_1_1,VK_KHR_external_memory[]

If pname:oldLayout is not equal to pname:newLayout, then the memory barrier
defines an <<synchronization-image-layout-transitions, image layout
transition>> for the specified image subresource range.
If this memory barrier defines a <<synchronization-queue-transfers, queue
family transfer operation>>, the layout transition is only executed once
between the queues.

[NOTE]
.Note
====
When the old and new layout are equal, the layout values are ignored - data
is preserved no matter what values are specified, or what layout the image
is currently in.
====

ifdef::VK_VERSION_1_1,VK_KHR_sampler_ycbcr_conversion[]

If pname:image has a multi-planar format and the image is _disjoint_, then
including ename:VK_IMAGE_ASPECT_COLOR_BIT in the pname:aspectMask member of
pname:subresourceRange is equivalent to including
ename:VK_IMAGE_ASPECT_PLANE_0_BIT, ename:VK_IMAGE_ASPECT_PLANE_1_BIT, and
(for three-plane formats only) ename:VK_IMAGE_ASPECT_PLANE_2_BIT.

endif::VK_VERSION_1_1,VK_KHR_sampler_ycbcr_conversion[]

.Valid Usage
****

:stageMaskName: srcStageMask
:accessMaskName: srcAccessMask
include::{chapters}/commonvalidity/stage_mask_2_common.txt[]
include::{chapters}/commonvalidity/access_mask_2_common.txt[]

:stageMaskName: dstStageMask
:accessMaskName: dstAccessMask
include::{chapters}/commonvalidity/stage_mask_2_common.txt[]
include::{chapters}/commonvalidity/access_mask_2_common.txt[]
include::{chapters}/commonvalidity/image_memory_barrier_common.txt[]
  * [[VUID-VkImageMemoryBarrier2KHR-srcStageMask-03854]]
    If either pname:srcStageMask or pname:dstStageMask includes
    ename:VK_PIPELINE_STAGE_2_HOST_BIT_KHR, pname:srcQueueFamilyIndex and
    pname:dstQueueFamilyIndex must: be equal
  * [[VUID-VkImageMemoryBarrier2KHR-srcStageMask-03855]]
    If pname:srcStageMask includes ename:VK_PIPELINE_STAGE_2_HOST_BIT_KHR,
    and pname:srcQueueFamilyIndex and pname:dstQueueFamilyIndex define a
    <<synchronization-queue-transfers, queue family ownership transfer>> or
    pname:oldLayout and pname:newLayout define an
    <<synchronization-image-layout-transitions, image layout transition>>,
    pname:oldLayout must: be one of ename:VK_IMAGE_LAYOUT_PREINITIALIZED,
    ename:VK_IMAGE_LAYOUT_UNDEFINED, or ename:VK_IMAGE_LAYOUT_GENERAL
****

include::{generated}/validity/structs/VkImageMemoryBarrier2KHR.txt[]
--
endif::VK_KHR_synchronization2[]

[open,refpage='VkImageMemoryBarrier',desc='Structure specifying the parameters of an image memory barrier',type='structs']
--
:refpage: VkImageMemoryBarrier

The sname:VkImageMemoryBarrier structure is defined as:

include::{generated}/api/structs/VkImageMemoryBarrier.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:srcAccessMask is a bitmask of elink:VkAccessFlagBits specifying a
    <<synchronization-access-masks, source access mask>>.
  * pname:dstAccessMask is a bitmask of elink:VkAccessFlagBits specifying a
    <<synchronization-access-masks, destination access mask>>.
  * pname:oldLayout is the old layout in an
    <<synchronization-image-layout-transitions, image layout transition>>.
  * pname:newLayout is the new layout in an
    <<synchronization-image-layout-transitions, image layout transition>>.
  * pname:srcQueueFamilyIndex is the source queue family for a
    <<synchronization-queue-transfers, queue family ownership transfer>>.
  * pname:dstQueueFamilyIndex is the destination queue family for a
    <<synchronization-queue-transfers, queue family ownership transfer>>.
  * pname:image is a handle to the image affected by this barrier.
  * pname:subresourceRange describes the <<resources-image-views, image
    subresource range>> within pname:image that is affected by this barrier.

The first <<synchronization-dependencies-access-scopes, access scope>> is
limited to access to memory through the specified image subresource range,
via access types in the <<synchronization-access-masks, source access mask>>
specified by pname:srcAccessMask.
If pname:srcAccessMask includes ename:VK_ACCESS_HOST_WRITE_BIT, memory
writes performed by that access type are also made visible, as that access
type is not performed through a resource.

The second <<synchronization-dependencies-access-scopes, access scope>> is
limited to access to memory through the specified image subresource range,
via access types in the <<synchronization-access-masks, destination access
mask>> specified by pname:dstAccessMask.
If pname:dstAccessMask includes ename:VK_ACCESS_HOST_WRITE_BIT or
ename:VK_ACCESS_HOST_READ_BIT, available memory writes are also made visible
to accesses of those types, as those access types are not performed through
a resource.

If pname:srcQueueFamilyIndex is not equal to pname:dstQueueFamilyIndex, and
pname:srcQueueFamilyIndex is equal to the current queue family, then the
memory barrier defines a <<synchronization-queue-transfers-release, queue
family release operation>> for the specified image subresource range, and
the second access scope includes no access, as if pname:dstAccessMask was
`0`.

If pname:dstQueueFamilyIndex is not equal to pname:srcQueueFamilyIndex, and
pname:dstQueueFamilyIndex is equal to the current queue family, then the
memory barrier defines a <<synchronization-queue-transfers-acquire, queue
family acquire operation>> for the specified image subresource range, and
the first access scope includes no access, as if pname:srcAccessMask was
`0`.

ifdef::VK_KHR_synchronization2[]
If the <<features-synchronization2,pname:synchronization2 feature>> is not
enabled or pname:oldLayout is not equal to pname:newLayout,
endif::VK_KHR_synchronization2[]
pname:oldLayout and pname:newLayout define an
<<synchronization-image-layout-transitions, image layout transition>> for
the specified image subresource range.

ifdef::VK_KHR_synchronization2[]
[NOTE]
.Note
====
If the <<features-synchronization2,pname:synchronization2 feature>> is
enabled, when the old and new layout are equal, the layout values are
ignored - data is preserved no matter what values are specified, or what
layout the image is currently in.
====
endif::VK_KHR_synchronization2[]

ifdef::VK_VERSION_1_1,VK_KHR_sampler_ycbcr_conversion[]

If pname:image has a multi-planar format and the image is _disjoint_, then
including ename:VK_IMAGE_ASPECT_COLOR_BIT in the pname:aspectMask member of
pname:subresourceRange is equivalent to including
ename:VK_IMAGE_ASPECT_PLANE_0_BIT, ename:VK_IMAGE_ASPECT_PLANE_1_BIT, and
(for three-plane formats only) ename:VK_IMAGE_ASPECT_PLANE_2_BIT.

endif::VK_VERSION_1_1,VK_KHR_sampler_ycbcr_conversion[]

.Valid Usage
****
include::{chapters}/commonvalidity/image_memory_barrier_common.txt[]
ifndef::VK_VERSION_1_1,VK_KHR_external_memory[]
  * [[VUID-VkImageMemoryBarrier-synchronization2-03856]]
    If the <<features-synchronization2,pname:synchronization2 feature>> is
    not enabled, and pname:image was created with a sharing mode of
    ename:VK_SHARING_MODE_CONCURRENT, pname:srcQueueFamilyIndex and
    pname:dstQueueFamilyIndex must: both be ename:VK_QUEUE_FAMILY_IGNORED
endif::VK_VERSION_1_1,VK_KHR_external_memory[]
ifdef::VK_VERSION_1_1,VK_KHR_external_memory[]
  * [[VUID-VkImageMemoryBarrier-synchronization2-03857]]
    If the <<features-synchronization2,pname:synchronization2 feature>> is
    not enabled, and pname:image was created with a sharing mode of
    ename:VK_SHARING_MODE_CONCURRENT, at least one of
    pname:srcQueueFamilyIndex and pname:dstQueueFamilyIndex must: be
    ename:VK_QUEUE_FAMILY_IGNORED
endif::VK_VERSION_1_1,VK_KHR_external_memory[]
****

include::{generated}/validity/structs/VkImageMemoryBarrier.txt[]
--


[[synchronization-queue-transfers]]
=== Queue Family Ownership Transfer

Resources created with a elink:VkSharingMode of
ename:VK_SHARING_MODE_EXCLUSIVE must: have their ownership explicitly
transferred from one queue family to another in order to access their
content in a well-defined manner on a queue in a different queue family.

[open,refpage='VK_QUEUE_FAMILY_IGNORED',desc='Ignored queue family index sentinel',type='consts']
--
The special queue family index ename:VK_QUEUE_FAMILY_IGNORED indicates that
a queue family parameter or member is ignored.

include::{generated}/api/enums/VK_QUEUE_FAMILY_IGNORED.txt[]
--

ifdef::VK_VERSION_1_1,VK_KHR_external_memory[]
Resources shared with external APIs or instances using external memory must:
also explicitly manage ownership transfers between local and external queues
(or equivalent constructs in external APIs) regardless of the
elink:VkSharingMode specified when creating them.

[open,refpage='VK_QUEUE_FAMILY_EXTERNAL',desc='External queue family index sentinel',type='consts',alias='VK_QUEUE_FAMILY_EXTERNAL_KHR']
--
The special queue family index ename:VK_QUEUE_FAMILY_EXTERNAL represents any
queue external to the resource's current Vulkan instance, as long as the
queue uses the same underlying
ifdef::VK_VERSION_1_1,VK_KHR_device_group[device group or]
physical device, and the same driver version as the resource's
slink:VkDevice, as indicated by
slink:VkPhysicalDeviceIDProperties::pname:deviceUUID and
slink:VkPhysicalDeviceIDProperties::pname:driverUUID.

include::{generated}/api/enums/VK_QUEUE_FAMILY_EXTERNAL.txt[]

ifdef::VK_KHR_external_memory[]
or the equivalent

include::{generated}/api/enums/VK_QUEUE_FAMILY_EXTERNAL_KHR.txt[]
endif::VK_KHR_external_memory[]
--

ifdef::VK_EXT_queue_family_foreign[]
[open,refpage='VK_QUEUE_FAMILY_FOREIGN_EXT',desc='Foreign queue family index sentinel',type='consts']
--
The special queue family index ename:VK_QUEUE_FAMILY_FOREIGN_EXT represents
any queue external to the resource's current Vulkan instance, regardless of
the queue's underlying physical device or driver version.
This includes, for example, queues for fixed-function image processing
devices, media codec devices, and display devices, as well as all queues
that use the same underlying
ifdef::VK_VERSION_1_1,VK_KHR_device_group[device group or]
physical device, and the same driver version as the resource's
slink:VkDevice.

include::{generated}/api/enums/VK_QUEUE_FAMILY_FOREIGN_EXT.txt[]
--
endif::VK_EXT_queue_family_foreign[]
endif::VK_VERSION_1_1,VK_KHR_external_memory[]

If memory dependencies are correctly expressed between uses of such a
resource between two queues in different families, but no ownership transfer
is defined, the contents of that resource are undefined: for any read
accesses performed by the second queue family.

[NOTE]
.Note
====
If an application does not need the contents of a resource to remain valid
when transferring from one queue family to another, then the ownership
transfer should: be skipped.
====

ifdef::VK_EXT_queue_family_foreign[]
[NOTE]
.Note
====
Applications should expect transfers to/from
ename:VK_QUEUE_FAMILY_FOREIGN_EXT to be more expensive than transfers
to/from ename:VK_QUEUE_FAMILY_EXTERNAL_KHR.
====
endif::VK_EXT_queue_family_foreign[]

A queue family ownership transfer consists of two distinct parts:

  . Release exclusive ownership from the source queue family
  . Acquire exclusive ownership for the destination queue family

An application must: ensure that these operations occur in the correct order
by defining an execution dependency between them, e.g. using a semaphore.

[[synchronization-queue-transfers-release]] A _release operation_ is used to
release exclusive ownership of a range of a buffer or image subresource
range.
A release operation is defined by executing a
<<synchronization-buffer-memory-barriers, buffer memory barrier>> (for a
buffer range) or an <<synchronization-image-memory-barriers, image memory
barrier>> (for an image subresource range) using a pipeline barrier command,
on a queue from the source queue family.
The pname:srcQueueFamilyIndex parameter of the barrier must: be set to the
source queue family index, and the pname:dstQueueFamilyIndex parameter to
the destination queue family index.
pname:dstAccessMask is ignored for such a barrier, such that no visibility
operation is executed - the value of this mask does not affect the validity
of the barrier.
The release operation happens-after the availability operation, and
happens-before operations specified in the second synchronization scope of
the calling command.

[[synchronization-queue-transfers-acquire]] An _acquire operation_ is used
to acquire exclusive ownership of a range of a buffer or image subresource
range.
An acquire operation is defined by executing a
<<synchronization-buffer-memory-barriers, buffer memory barrier>> (for a
buffer range) or an <<synchronization-image-memory-barriers, image memory
barrier>> (for an image subresource range) using a pipeline barrier command,
on a queue from the destination queue family.
The buffer range or image subresource range specified in an acquire
operation must: match exactly that of a previous release operation.
The pname:srcQueueFamilyIndex parameter of the barrier must: be set to the
source queue family index, and the pname:dstQueueFamilyIndex parameter to
the destination queue family index.
pname:srcAccessMask is ignored for such a barrier, such that no availability
operation is executed - the value of this mask does not affect the validity
of the barrier.
The acquire operation happens-after operations in the first synchronization
scope of the calling command, and happens-before the visibility operation.

[NOTE]
.Note
====
Whilst it is not invalid to provide destination or source access masks for
memory barriers used for release or acquire operations, respectively, they
have no practical effect.
Access after a release operation has undefined: results, and so visibility
for those accesses has no practical effect.
Similarly, write access before an acquire operation will produce undefined:
results for future access, so availability of those writes has no practical
use.
In an earlier version of the specification, these were required to match on
both sides - but this was subsequently relaxed.
These masks should: be set to 0.
====

If the transfer is via an image memory barrier, and an
<<synchronization-image-layout-transitions, image layout transition>> is
desired, then the values of pname:oldLayout and pname:newLayout in the
_release operation_'s memory barrier must: be equal to values of
pname:oldLayout and pname:newLayout in the _acquire operation_'s memory
barrier.
Although the image layout transition is submitted twice, it will only be
executed once.
A layout transition specified in this way happens-after the _release
operation_ and happens-before the _acquire operation_.

If the values of pname:srcQueueFamilyIndex and pname:dstQueueFamilyIndex are
equal, no ownership transfer is performed, and the barrier operates as if
they were both set to ename:VK_QUEUE_FAMILY_IGNORED.

Queue family ownership transfers may: perform read and write accesses on all
memory bound to the image subresource or buffer range, so applications must:
ensure that all memory writes have been made
<<synchronization-dependencies-available-and-visible, available>> before a
queue family ownership transfer is executed.
Available memory is automatically made visible to queue family release and
acquire operations, and writes performed by those operations are
automatically made available.

Once a queue family has acquired ownership of a buffer range or image
subresource range of a ename:VK_SHARING_MODE_EXCLUSIVE resource, its
contents are undefined: to other queue families unless ownership is
transferred.
The contents of any portion of another resource which aliases memory that is
bound to the transferred buffer or image subresource range are undefined:
after a release or acquire operation.

[NOTE]
.Note
====
Because <<synchronization-events, events>> cannot: be used directly for
inter-queue synchronization, and because flink:vkCmdSetEvent does not have
the queue family index or memory barrier parameters needed by a _release
operation_, the release and acquire operations of a queue family ownership
transfer can: only be performed using flink:vkCmdPipelineBarrier.
====


[[synchronization-wait-idle]]
== Wait Idle Operations

[open,refpage='vkQueueWaitIdle',desc='Wait for a queue to become idle',type='protos']
--
To wait on the host for the completion of outstanding queue operations for a
given queue, call:

include::{generated}/api/protos/vkQueueWaitIdle.txt[]

  * pname:queue is the queue on which to wait.

fname:vkQueueWaitIdle is equivalent to having submitted a valid fence to
every previously executed <<devsandqueues-submission,queue submission
command>> that accepts a fence, then waiting for all of those fences to
signal using flink:vkWaitForFences with an infinite timeout and
pname:waitAll set to ename:VK_TRUE.

include::{generated}/validity/protos/vkQueueWaitIdle.txt[]
--

[open,refpage='vkDeviceWaitIdle',desc='Wait for a device to become idle',type='protos']
--
To wait on the host for the completion of outstanding queue operations for
all queues on a given logical device, call:

include::{generated}/api/protos/vkDeviceWaitIdle.txt[]

  * pname:device is the logical device to idle.

fname:vkDeviceWaitIdle is equivalent to calling fname:vkQueueWaitIdle for
all queues owned by pname:device.

include::{generated}/validity/protos/vkDeviceWaitIdle.txt[]
--


[[synchronization-submission-host-writes]]
== Host Write Ordering Guarantees

When batches of command buffers are submitted to a queue via a
<<devsandqueues-submission, queue submission command>>, it defines a memory
dependency with prior host operations, and execution of command buffers
submitted to the queue.

The first <<synchronization-dependencies-scopes, synchronization scope>> is
defined by the host execution model, but includes execution of
flink:vkQueueSubmit on the host and anything that happened-before it.

The second <<synchronization-dependencies-scopes, synchronization scope>>
includes all commands submitted in the same <<devsandqueues-submission,
queue submission>>, and all commands that occur later in
<<synchronization-submission-order,submission order>>.

The first <<synchronization-dependencies-access-scopes, access scope>>
includes all host writes to mappable device memory that are available to the
host memory domain.

The second <<synchronization-dependencies-access-scopes, access scope>>
includes all memory access performed by the device.


ifdef::VK_VERSION_1_1,VK_KHR_device_group[]
[[synchronization-device-group]]
== Synchronization and Multiple Physical Devices

If a logical device includes more than one physical device, then fences,
semaphores, and events all still have a single instance of the signaled
state.

A fence becomes signaled when all physical devices complete the necessary
queue operations.

Semaphore wait and signal operations all include a device index that is the
sole physical device that performs the operation.
These indices are provided in the slink:VkDeviceGroupSubmitInfo and
slink:VkDeviceGroupBindSparseInfo structures.
Semaphores are not exclusively owned by any physical device.
For example, a semaphore can be signaled by one physical device and then
waited on by a different physical device.

An event can: only be waited on by the same physical device that signaled it
(or the host).
endif::VK_VERSION_1_1,VK_KHR_device_group[]


ifdef::VK_EXT_calibrated_timestamps[]
[[calibrated-timestamps]]
== Calibrated timestamps

[open,refpage='vkGetCalibratedTimestampsEXT',desc='Query calibrated timestamps',type='protos']
--
In order to be able to correlate the time a particular operation took place
at on timelines of different time domains (e.g. a device operation vs a host
operation), Vulkan allows querying calibrated timestamps from multiple time
domains.

To query calibrated timestamps from a set of time domains, call:

include::{generated}/api/protos/vkGetCalibratedTimestampsEXT.txt[]

  * pname:device is the logical device used to perform the query.
  * pname:timestampCount is the number of timestamps to query.
  * pname:pTimestampInfos is a pointer to an array of pname:timestampCount
    slink:VkCalibratedTimestampInfoEXT structures, describing the time
    domains the calibrated timestamps should be captured from.
  * pname:pTimestamps is a pointer to an array of pname:timestampCount
    64-bit unsigned integer values in which the requested calibrated
    timestamp values are returned.
  * pname:pMaxDeviation is a pointer to a 64-bit unsigned integer value in
    which the strictly positive maximum deviation, in nanoseconds, of the
    calibrated timestamp values is returned.

[NOTE]
.Note
====
The maximum deviation may: vary between calls to
fname:vkGetCalibratedTimestampsEXT even for the same set of time domains due
to implementation and platform specific reasons.
It is the application's responsibility to assess whether the returned
maximum deviation makes the timestamp values suitable for any particular
purpose and can: choose to re-issue the timestamp calibration call pursuing
a lower devation value.
====

Calibrated timestamp values can: be extrapolated to estimate future
coinciding timestamp values, however, depending on the nature of the time
domains and other properties of the platform extrapolating values over a
sufficiently long period of time may: no longer be accurate enough to fit
any particular purpose, so applications are expected to re-calibrate the
timestamps on a regular basis.

include::{generated}/validity/protos/vkGetCalibratedTimestampsEXT.txt[]
--

[open,refpage='VkCalibratedTimestampInfoEXT',desc='Structure specifying the input parameters of a calibrated timestamp query',type='structs']
--
The sname:VkCalibratedTimestampInfoEXT structure is defined as:

include::{generated}/api/structs/VkCalibratedTimestampInfoEXT.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:timeDomain is a elink:VkTimeDomainEXT value specifying the time
    domain from which the calibrated timestamp value should be returned.

.Valid Usage
****
  * [[VUID-VkCalibratedTimestampInfoEXT-timeDomain-02354]]
    pname:timeDomain must: be one of the elink:VkTimeDomainEXT values
    returned by flink:vkGetPhysicalDeviceCalibrateableTimeDomainsEXT
****
include::{generated}/validity/structs/VkCalibratedTimestampInfoEXT.txt[]
--

[open,refpage='VkTimeDomainEXT',desc='Supported time domains',type='enums']
--
The set of supported time domains consists of:

include::{generated}/api/enums/VkTimeDomainEXT.txt[]

  * ename:VK_TIME_DOMAIN_DEVICE_EXT specifies the device time domain.
    Timestamp values in this time domain use the same units and are
    comparable with device timestamp values captured using
    flink:vkCmdWriteTimestamp
ifdef::VK_KHR_synchronization2[]
    or flink:vkCmdWriteTimestamp2KHR
endif::VK_KHR_synchronization2[]
    and are defined to be incrementing according to the
    <<limits-timestampPeriod,timestampPeriod>> of the device.

  * ename:VK_TIME_DOMAIN_CLOCK_MONOTONIC_EXT specifies the CLOCK_MONOTONIC
    time domain available on POSIX platforms.
    Timestamp values in this time domain are in units of nanoseconds and are
    comparable with platform timestamp values captured using the POSIX
    clock_gettime API as computed by this example:

[NOTE]
.Note
====
An implementation supporting `apiext:VK_EXT_calibrated_timestamps` will use
the same time domain for all its slink:VkQueue so that timestamp values
reported for ename:VK_TIME_DOMAIN_DEVICE_EXT can be matched to any timestamp
captured through flink:vkCmdWriteTimestamp
ifdef::VK_KHR_synchronization2[]
or flink:vkCmdWriteTimestamp2KHR
endif::VK_KHR_synchronization2[]
.
====

[source,c]
~~~~
struct timespec tv;
clock_gettime(CLOCK_MONOTONIC, &tv);
return tv.tv_nsec + tv.tv_sec*1000000000ull;
~~~~

  * ename:VK_TIME_DOMAIN_CLOCK_MONOTONIC_RAW_EXT specifies the
    CLOCK_MONOTONIC_RAW time domain available on POSIX platforms.
    Timestamp values in this time domain are in units of nanoseconds and are
    comparable with platform timestamp values captured using the POSIX
    clock_gettime API as computed by this example:

[source,c]
~~~~
struct timespec tv;
clock_gettime(CLOCK_MONOTONIC_RAW, &tv);
return tv.tv_nsec + tv.tv_sec*1000000000ull;
~~~~

  * ename:VK_TIME_DOMAIN_QUERY_PERFORMANCE_COUNTER_EXT specifies the
    performance counter (QPC) time domain available on Windows.
    Timestamp values in this time domain are in the same units as those
    provided by the Windows QueryPerformanceCounter API and are comparable
    with platform timestamp values captured using that API as computed by
    this example:

[source,c]
~~~~
LARGE_INTEGER counter;
QueryPerformanceCounter(&counter);
return counter.QuadPart;
~~~~
--
endif::VK_EXT_calibrated_timestamps[]