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// Copyright (c) 2009 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_ATOMIC_FLAG_H_
#define BASE_ATOMIC_FLAG_H_
#include "base/atomicops.h"
namespace base {
// AtomicFlag allows threads to notify each other for a single occurrence
// of a single event. It maintains an abstract boolean "flag" that transitions
// to true at most once. It provides calls to query the boolean.
//
// Memory ordering: For any threads X and Y, if X calls Set(), then any
// action taken by X before it calls Set() is visible to thread Y after
// Y receives a true return value from IsSet().
class AtomicFlag {
public:
// Sets "flag_" to "initial_value".
explicit AtomicFlag(bool initial_value = false)
: flag_(initial_value ? 1 : 0) { }
~AtomicFlag() {}
void Set(); // Set "flag_" to true. May be called only once.
bool IsSet() const; // Return "flag_".
private:
base::subtle::Atomic32 flag_;
DISALLOW_COPY_AND_ASSIGN(AtomicFlag);
};
} // namespace base
#endif // BASE_ATOMIC_FLAG_H_
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