| /* |
| * 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 PerProcess_h |
| #define PerProcess_h |
| |
| #include "Inline.h" |
| #include "Sizes.h" |
| #include "StaticMutex.h" |
| #include <mutex> |
| |
| namespace bmalloc { |
| |
| // Usage: |
| // Object* object = PerProcess<Object>::get(); |
| // x = object->field->field; |
| // |
| // Object will be instantiated only once, even in the face of concurrency. |
| // |
| // NOTE: If you observe global side-effects of the Object constructor, be |
| // sure to lock the Object mutex. For example: |
| // |
| // Object() : m_field(...) { globalFlag = true } |
| // |
| // Object* object = PerProcess<Object>::get(); |
| // x = object->m_field; // OK |
| // if (globalFlag) { ... } // Undefined behavior. |
| // |
| // std::lock_guard<StaticMutex> lock(PerProcess<Object>::mutex()); |
| // Object* object = PerProcess<Object>::get(lock); |
| // if (globalFlag) { ... } // OK. |
| |
| template<typename T> |
| class PerProcess { |
| public: |
| static T* get(); |
| static T* getFastCase(); |
| |
| static StaticMutex& mutex() { return s_mutex; } |
| |
| private: |
| static T* getSlowCase(); |
| |
| static std::atomic<T*> s_object; |
| static StaticMutex s_mutex; |
| |
| typedef typename std::aligned_storage<sizeof(T), std::alignment_of<T>::value>::type Memory; |
| static Memory s_memory; |
| }; |
| |
| template<typename T> |
| INLINE T* PerProcess<T>::getFastCase() |
| { |
| return s_object.load(std::memory_order_consume); |
| } |
| |
| template<typename T> |
| INLINE T* PerProcess<T>::get() |
| { |
| T* object = getFastCase(); |
| if (!object) |
| return getSlowCase(); |
| return object; |
| } |
| |
| template<typename T> |
| NO_INLINE T* PerProcess<T>::getSlowCase() |
| { |
| std::lock_guard<StaticMutex> lock(s_mutex); |
| if (!s_object.load(std::memory_order_consume)) { |
| T* t = new (&s_memory) T(lock); |
| s_object.store(t, std::memory_order_release); |
| } |
| return s_object.load(std::memory_order_consume); |
| } |
| |
| template<typename T> |
| std::atomic<T*> PerProcess<T>::s_object; |
| |
| template<typename T> |
| StaticMutex PerProcess<T>::s_mutex; |
| |
| template<typename T> |
| typename PerProcess<T>::Memory PerProcess<T>::s_memory; |
| |
| } // namespace bmalloc |
| |
| #endif // PerProcess_h |