1// Copyright 2010 the V8 project authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef V8_PROFILER_CIRCULAR_QUEUE_H_
6#define V8_PROFILER_CIRCULAR_QUEUE_H_
7
8#include "src/base/atomicops.h"
9#include "src/common/globals.h"
10
11namespace v8 {
12namespace internal {
13
14// Lock-free cache-friendly sampling circular queue for large
15// records. Intended for fast transfer of large records between a
16// single producer and a single consumer. If the queue is full,
17// StartEnqueue will return nullptr. The queue is designed with
18// a goal in mind to evade cache lines thrashing by preventing
19// simultaneous reads and writes to adjanced memory locations.
20template<typename T, unsigned Length>
21class SamplingCircularQueue {
22 public:
23  // Executed on the application thread.
24  SamplingCircularQueue();
25  ~SamplingCircularQueue();
26  SamplingCircularQueue(const SamplingCircularQueue&) = delete;
27  SamplingCircularQueue& operator=(const SamplingCircularQueue&) = delete;
28
29  // StartEnqueue returns a pointer to a memory location for storing the next
30  // record or nullptr if all entries are full at the moment.
31  T* StartEnqueue();
32  // Notifies the queue that the producer has complete writing data into the
33  // memory returned by StartEnqueue and it can be passed to the consumer.
34  void FinishEnqueue();
35
36  // Executed on the consumer (analyzer) thread.
37  // Retrieves, but does not remove, the head of this queue, returning nullptr
38  // if this queue is empty. After the record had been read by a consumer,
39  // Remove must be called.
40  T* Peek();
41  void Remove();
42
43 private:
44  // Reserved values for the entry marker.
45  enum {
46    kEmpty,  // Marks clean (processed) entries.
47    kFull    // Marks entries already filled by the producer but not yet
48             // completely processed by the consumer.
49  };
50
51  struct alignas(PROCESSOR_CACHE_LINE_SIZE) Entry {
52    Entry() : marker(kEmpty) {}
53    T record;
54    base::Atomic32 marker;
55  };
56
57  Entry* Next(Entry* entry);
58
59  Entry buffer_[Length];
60  alignas(PROCESSOR_CACHE_LINE_SIZE) Entry* enqueue_pos_;
61  alignas(PROCESSOR_CACHE_LINE_SIZE) Entry* dequeue_pos_;
62};
63
64
65}  // namespace internal
66}  // namespace v8
67
68#endif  // V8_PROFILER_CIRCULAR_QUEUE_H_
69