1// Copyright (c) 2011 The Chromium 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 BASE_SYNCHRONIZATION_ATOMIC_FLAG_H_
6#define BASE_SYNCHRONIZATION_ATOMIC_FLAG_H_
7
8#include "base/atomicops.h"
9#include "base/base_export.h"
10#include "base/macros.h"
11#include "base/sequence_checker.h"
12
13namespace base {
14
15// A flag that can safely be set from one thread and read from other threads.
16//
17// This class IS NOT intended for synchronization between threads.
18class BASE_EXPORT AtomicFlag {
19 public:
20  AtomicFlag();
21  ~AtomicFlag() = default;
22
23  // Set the flag. Must always be called from the same sequence.
24  void Set();
25
26  // Returns true iff the flag was set. If this returns true, the current thread
27  // is guaranteed to be synchronized with all memory operations on the sequence
28  // which invoked Set() up until at least the first call to Set() on it.
29  bool IsSet() const;
30
31  // Resets the flag. Be careful when using this: callers might not expect
32  // IsSet() to return false after returning true once.
33  void UnsafeResetForTesting();
34
35 private:
36  base::subtle::Atomic32 flag_ = 0;
37  SequenceChecker set_sequence_checker_;
38
39  DISALLOW_COPY_AND_ASSIGN(AtomicFlag);
40};
41
42}  // namespace base
43
44#endif  // BASE_SYNCHRONIZATION_ATOMIC_FLAG_H_
45