| // 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_ |