// 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 #include #include "base/base_export.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(const AtomicFlag&) = delete; AtomicFlag& operator=(const AtomicFlag&) = delete; ~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 flag_{0}; SEQUENCE_CHECKER(set_sequence_checker_); }; } // namespace base #endif // BASE_SYNCHRONIZATION_ATOMIC_FLAG_H_