atomic_flag.h - mozsearch

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// Copyright (c) 2011 The Chromium Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file.

#ifndef BASE_SYNCHRONIZATION_ATOMIC_FLAG_H_

#define BASE_SYNCHRONIZATION_ATOMIC_FLAG_H_

#include <stdint.h>

#include <atomic>

#include "base/base_export.h"

#include "base/macros.h"

#include "base/sequence_checker.h"

namespace base {

// A flag that can safely be set from one thread and read from other threads.

//

// This class IS NOT intended for synchronization between threads.

class BASE_EXPORT AtomicFlag {

 public:

  AtomicFlag();

  ~AtomicFlag();

  // Set the flag. Must always be called from the same sequence.

  void Set();

  // Returns true iff the flag was set. If this returns true, the current thread

  // is guaranteed to be synchronized with all memory operations on the sequence

  // which invoked Set() up until at least the first call to Set() on it.

  bool IsSet() const {

    // Inline here: this has a measurable performance impact on base::WeakPtr.

    return flag_.load(std::memory_order_acquire) != 0;

  // Resets the flag. Be careful when using this: callers might not expect

  // IsSet() to return false after returning true once.

  void UnsafeResetForTesting();

 private:

  std::atomic<uint_fast8_t> flag_{0};

  SEQUENCE_CHECKER(set_sequence_checker_);

  DISALLOW_COPY_AND_ASSIGN(AtomicFlag);

};

}  // namespace base

#endif  // BASE_SYNCHRONIZATION_ATOMIC_FLAG_H_