51 lines
1.4 KiB
C++
51 lines
1.4 KiB
C++
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_SYNCHRONIZATION_ATOMIC_FLAG_H_
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#define BASE_SYNCHRONIZATION_ATOMIC_FLAG_H_
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#include <stdint.h>
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#include <atomic>
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#include "base/base_export.h"
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#include "base/macros.h"
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#include "base/sequence_checker.h"
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namespace base {
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// A flag that can safely be set from one thread and read from other threads.
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//
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// This class IS NOT intended for synchronization between threads.
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class BASE_EXPORT AtomicFlag {
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public:
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AtomicFlag();
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~AtomicFlag();
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// Set the flag. Must always be called from the same sequence.
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void Set();
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// Returns true iff the flag was set. If this returns true, the current thread
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// is guaranteed to be synchronized with all memory operations on the sequence
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// which invoked Set() up until at least the first call to Set() on it.
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bool IsSet() const {
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// Inline here: this has a measurable performance impact on base::WeakPtr.
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return flag_.load(std::memory_order_acquire) != 0;
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}
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// Resets the flag. Be careful when using this: callers might not expect
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// IsSet() to return false after returning true once.
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void UnsafeResetForTesting();
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private:
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std::atomic<uint_fast8_t> flag_{0};
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SEQUENCE_CHECKER(set_sequence_checker_);
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DISALLOW_COPY_AND_ASSIGN(AtomicFlag);
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};
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} // namespace base
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#endif // BASE_SYNCHRONIZATION_ATOMIC_FLAG_H_
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