1/* 2 * Copyright (C) 2014 Apple Inc. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY 14 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 16 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR 17 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 18 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 19 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 20 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY 21 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 23 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 24 */ 25 26#ifndef StaticMutex_h 27#define StaticMutex_h 28 29#include "BAssert.h" 30#include <atomic> 31 32// A fast replacement for std::mutex for use in static storage, where global 33// constructors and exit-time destructors are prohibited. 34 35namespace bmalloc { 36 37class StaticMutex { 38public: 39 void lock(); 40 bool try_lock(); 41 void unlock(); 42 43private: 44 friend class Mutex; 45 46 // Static storage will zero-initialize us automatically, but Mutex needs an 47 // API for explicit initialization. 48 void init(); 49 50 void lockSlowCase(); 51 52 std::atomic_flag m_flag; 53}; 54 55inline void StaticMutex::init() 56{ 57 m_flag.clear(); 58} 59 60inline bool StaticMutex::try_lock() 61{ 62 return !m_flag.test_and_set(std::memory_order_acquire); 63} 64 65inline void StaticMutex::lock() 66{ 67 if (!try_lock()) 68 lockSlowCase(); 69} 70 71inline void StaticMutex::unlock() 72{ 73 m_flag.clear(std::memory_order_release); 74} 75 76} // namespace bmalloc 77 78#endif // StaticMutex_h 79