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// Copyright 2015 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 COMPONENTS_SCHEDULER_BASE_POLLABLE_THREAD_SAFE_FLAG_H_
#define COMPONENTS_SCHEDULER_BASE_POLLABLE_THREAD_SAFE_FLAG_H_
#include "base/atomicops.h"
#include "base/macros.h"
#include "base/synchronization/lock.h"
// A PollableThreadSafeFlag can be polled without requiring a lock, but can only
// be updated if a lock is held. This enables lock-free checking as to whether a
// condition has changed, while protecting operations which update the condition
// with a lock. You must ensure that the flag is only updated within the same
// lock-protected critical section as any other variables on which the condition
// depends.
class PollableThreadSafeFlag {
public:
explicit PollableThreadSafeFlag(base::Lock* write_lock);
~PollableThreadSafeFlag();
// Set the flag. May only be called if |write_lock| is held.
void SetWhileLocked(bool value);
// Returns true iff the flag is set to true.
bool IsSet() const;
private:
base::subtle::Atomic32 flag_;
base::Lock* write_lock_; // Not owned.
DISALLOW_COPY_AND_ASSIGN(PollableThreadSafeFlag);
};
#endif // COMPONENTS_SCHEDULER_BASE_POLLABLE_THREAD_SAFE_FLAG_H_
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