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/*
* Copyright (C) 2014 Apple 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:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. 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.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``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 APPLE INC. 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 StaticMutex_h
#define StaticMutex_h
#include "BAssert.h"
#include <atomic>
#include <mutex>
#include <thread>
// A fast replacement for std::mutex, for use in static storage.
// Use StaticMutex in static storage, where global constructors and exit-time
// destructors are prohibited, but all memory is zero-initialized automatically.
namespace bmalloc {
class StaticMutex {
protected:
// Subclasses that support non-static storage must use explicit initialization.
void init();
public:
void lock();
bool try_lock();
void unlock();
private:
void lockSlowCase();
std::atomic_flag m_flag;
};
static inline void sleep(
std::unique_lock<StaticMutex>& lock, std::chrono::milliseconds duration)
{
if (duration == std::chrono::milliseconds(0))
return;
lock.unlock();
std::this_thread::sleep_for(duration);
lock.lock();
}
static inline void waitUntilFalse(
std::unique_lock<StaticMutex>& lock, std::chrono::milliseconds sleepDuration,
bool& condition)
{
while (condition) {
condition = false;
sleep(lock, sleepDuration);
}
}
inline void StaticMutex::init()
{
m_flag.clear();
}
inline bool StaticMutex::try_lock()
{
return !m_flag.test_and_set(std::memory_order_acquire);
}
inline void StaticMutex::lock()
{
if (!try_lock())
lockSlowCase();
}
inline void StaticMutex::unlock()
{
m_flag.clear(std::memory_order_release);
}
} // namespace bmalloc
#endif // StaticMutex_h
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