1// Copyright 2020 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_HEAP_COLLECTION_BARRIER_H_
6#define V8_HEAP_COLLECTION_BARRIER_H_
7
8#include <atomic>
9
10#include "src/base/optional.h"
11#include "src/base/platform/condition-variable.h"
12#include "src/base/platform/elapsed-timer.h"
13#include "src/base/platform/mutex.h"
14#include "src/heap/local-heap.h"
15#include "src/logging/counters.h"
16
17namespace v8 {
18namespace internal {
19
20class Heap;
21
22// This class stops and resumes all background threads waiting for GC.
23class CollectionBarrier {
24 public:
25  explicit CollectionBarrier(Heap* heap) : heap_(heap) {}
26
27  // Returns true when collection was requested.
28  bool WasGCRequested();
29
30  // Requests a GC from the main thread. Returns whether GC was successfully
31  // requested. Requesting a GC can fail when isolate shutdown was already
32  // initiated.
33  bool TryRequestGC();
34
35  // Resumes all threads waiting for GC when tear down starts.
36  void NotifyShutdownRequested();
37
38  // Stops the TimeToCollection timer when starting the GC.
39  void StopTimeToCollectionTimer();
40
41  // Resumes threads waiting for collection.
42  void ResumeThreadsAwaitingCollection();
43
44  // Cancels collection if one was requested and resumes threads waiting for GC.
45  void CancelCollectionAndResumeThreads();
46
47  // This is the method use by background threads to request and wait for GC.
48  // Returns whether a GC was performed.
49  bool AwaitCollectionBackground(LocalHeap* local_heap);
50
51 private:
52  // Activate stack guards and posting a task to perform the GC.
53  void ActivateStackGuardAndPostTask();
54
55  Heap* heap_;
56  base::Mutex mutex_;
57  base::ConditionVariable cv_wakeup_;
58  base::ElapsedTimer timer_;
59
60  // Flag that main thread checks whether a GC was requested from the background
61  // thread.
62  std::atomic<bool> collection_requested_{false};
63
64  // This flag is used to detect whether to block for the GC. Only set if the
65  // main thread was actually running and is unset when GC resumes background
66  // threads.
67  bool block_for_collection_ = false;
68
69  // Set to true when a GC was performed, false in case it was canceled because
70  // the main thread parked itself without running the GC.
71  bool collection_performed_ = false;
72
73  // Will be set as soon as Isolate starts tear down.
74  bool shutdown_requested_ = false;
75};
76
77}  // namespace internal
78}  // namespace v8
79
80#endif  // V8_HEAP_COLLECTION_BARRIER_H_
81