/* * Copyright (C) 2014-2018 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. */ #pragma once #include "BInline.h" #include "Mutex.h" #include "Sizes.h" 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<Mutex> lock(PerProcess<Object>::mutex()); // Object* object = PerProcess<Object>::get(lock); // if (globalFlag) { ... } // OK. struct PerProcessData { const char* disambiguator; void* memory; size_t size; size_t alignment; Mutex mutex; bool isInitialized; PerProcessData* next; }; constexpr unsigned stringHash(const char* string) { unsigned result = 5381; while (char c = *string++) result = result * 33 + c; return result; } BEXPORT PerProcessData* getPerProcessData(unsigned disambiguatorHash, const char* disambiguator, size_t size, size_t alignment); template<typename T> class PerProcess { public: static T* get() { T* object = getFastCase(); if (!object) return getSlowCase(); return object; } static T* getFastCase() { return s_object.load(std::memory_order_relaxed); } static Mutex& mutex() { if (!s_data) coalesce(); return s_data->mutex; } private: static void coalesce() { if (s_data) return; const char* disambiguator = __PRETTY_FUNCTION__; s_data = getPerProcessData(stringHash(disambiguator), disambiguator, sizeof(T), std::alignment_of<T>::value); } BNO_INLINE static T* getSlowCase() { std::lock_guard<Mutex> lock(mutex()); if (!s_object.load()) { if (s_data->isInitialized) s_object.store(static_cast<T*>(s_data->memory)); else { T* t = new (s_data->memory) T(lock); s_object.store(t); s_data->isInitialized = true; } } return s_object.load(); } static std::atomic<T*> s_object; static PerProcessData* s_data; }; template<typename T> std::atomic<T*> PerProcess<T>::s_object { nullptr }; template<typename T> PerProcessData* PerProcess<T>::s_data { nullptr }; } // namespace bmalloc