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 PerProcess_h 27#define PerProcess_h 28 29#include "Inline.h" 30#include "Sizes.h" 31#include "StaticMutex.h" 32#include <mutex> 33 34namespace bmalloc { 35 36// Usage: 37// Object* object = PerProcess<Object>::get(); 38// x = object->field->field; 39// 40// Object will be instantiated only once, even in the face of concurrency. 41// 42// NOTE: If you observe global side-effects of the Object constructor, be 43// sure to lock the Object mutex. For example: 44// 45// Object() : m_field(...) { globalFlag = true } 46// 47// Object* object = PerProcess<Object>::get(); 48// x = object->m_field; // OK 49// if (gobalFlag) { ... } // Undefined behavior. 50// 51// std::lock_guard<StaticMutex> lock(PerProcess<Object>::mutex()); 52// Object* object = PerProcess<Object>::get(lock); 53// if (gobalFlag) { ... } // OK. 54 55template<typename T> 56class PerProcess { 57public: 58 static T* get(); 59 static T* getFastCase(); 60 61 static StaticMutex& mutex() { return s_mutex; } 62 63private: 64 static T* getSlowCase(); 65 66 static std::atomic<T*> s_object; 67 static StaticMutex s_mutex; 68 69 typedef typename std::aligned_storage<sizeof(T), std::alignment_of<T>::value>::type Memory; 70 static Memory s_memory; 71}; 72 73template<typename T> 74INLINE T* PerProcess<T>::getFastCase() 75{ 76 return s_object.load(std::memory_order_consume); 77} 78 79template<typename T> 80INLINE T* PerProcess<T>::get() 81{ 82 T* object = getFastCase(); 83 if (!object) 84 return getSlowCase(); 85 return object; 86} 87 88template<typename T> 89NO_INLINE T* PerProcess<T>::getSlowCase() 90{ 91 std::lock_guard<StaticMutex> lock(s_mutex); 92 if (!s_object.load(std::memory_order_consume)) { 93 T* t = new (&s_memory) T(lock); 94 s_object.store(t, std::memory_order_release); 95 } 96 return s_object.load(std::memory_order_consume); 97} 98 99template<typename T> 100std::atomic<T*> PerProcess<T>::s_object; 101 102template<typename T> 103StaticMutex PerProcess<T>::s_mutex; 104 105template<typename T> 106typename PerProcess<T>::Memory PerProcess<T>::s_memory; 107 108} // namespace bmalloc 109 110#endif // PerProcess_h 111