cef/include/base/cef_atomic_flag.h

98 lines
3.3 KiB
C++

// Copyright (c) 2014 Marshall A. Greenblatt. Portions copyright (c) 2011
// Google Inc. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the name Chromium Embedded
// Framework nor the names of its contributors may be used to endorse
// or promote products derived from this software without specific prior
// written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#ifndef CEF_INCLUDE_BASE_CEF_ATOMIC_FLAG_H_
#define CEF_INCLUDE_BASE_CEF_ATOMIC_FLAG_H_
#pragma once
#if defined(USING_CHROMIUM_INCLUDES)
// When building CEF include the Chromium header directly.
#include "base/synchronization/atomic_flag.h"
#else // !USING_CHROMIUM_INCLUDES
// The following is substantially similar to the Chromium implementation.
// If the Chromium implementation diverges the below implementation should be
// updated to match.
#include <stdint.h>
#include <atomic>
#include "include/base/cef_thread_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 AtomicFlag {
public:
AtomicFlag();
AtomicFlag(const AtomicFlag&) = delete;
AtomicFlag& operator=(const AtomicFlag&) = delete;
~AtomicFlag();
///
/// Set the flag. Must always be called from the same thread.
///
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
/// thread 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};
base::ThreadChecker set_thread_checker_;
};
} // namespace base
#endif // !USING_CHROMIUM_INCLUDES
#endif // CEF_INCLUDE_BASE_CEF_ATOMIC_FLAG_H_