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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_
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