132 lines
3.8 KiB
C++
132 lines
3.8 KiB
C++
/*
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* Copyright (C) 2014-2018 Apple Inc. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
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* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
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* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include "BInline.h"
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#include "Mutex.h"
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#include "Sizes.h"
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namespace bmalloc {
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// Usage:
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// Object* object = PerProcess<Object>::get();
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// x = object->field->field;
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//
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// Object will be instantiated only once, even in the face of concurrency.
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//
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// NOTE: If you observe global side-effects of the Object constructor, be
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// sure to lock the Object mutex. For example:
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//
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// Object() : m_field(...) { globalFlag = true }
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//
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// Object* object = PerProcess<Object>::get();
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// x = object->m_field; // OK
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// if (globalFlag) { ... } // Undefined behavior.
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//
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// LockHolder lock(PerProcess<Object>::mutex());
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// Object* object = PerProcess<Object>::get(lock);
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// if (globalFlag) { ... } // OK.
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struct PerProcessData {
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const char* disambiguator;
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void* memory;
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size_t size;
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size_t alignment;
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Mutex mutex;
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bool isInitialized;
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PerProcessData* next;
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};
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constexpr unsigned stringHash(const char* string)
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{
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unsigned result = 5381;
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while (char c = *string++)
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result = result * 33 + c;
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return result;
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}
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BEXPORT PerProcessData* getPerProcessData(unsigned disambiguatorHash, const char* disambiguator, size_t size, size_t alignment);
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template<typename T>
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class PerProcess {
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public:
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static T* get()
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{
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T* object = getFastCase();
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if (!object)
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return getSlowCase();
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return object;
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}
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static T* getFastCase()
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{
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return s_object.load(std::memory_order_relaxed);
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}
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static Mutex& mutex()
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{
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if (!s_data)
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coalesce();
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return s_data->mutex;
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}
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private:
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static void coalesce()
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{
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if (s_data)
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return;
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const char* disambiguator = __PRETTY_FUNCTION__;
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s_data = getPerProcessData(stringHash(disambiguator), disambiguator, sizeof(T), std::alignment_of<T>::value);
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}
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BNO_INLINE static T* getSlowCase()
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{
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LockHolder lock(mutex());
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if (!s_object.load()) {
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if (s_data->isInitialized)
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s_object.store(static_cast<T*>(s_data->memory));
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else {
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T* t = new (s_data->memory) T(lock);
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s_object.store(t);
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s_data->isInitialized = true;
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}
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}
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return s_object.load();
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}
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static std::atomic<T*> s_object;
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static PerProcessData* s_data;
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};
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template<typename T>
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std::atomic<T*> PerProcess<T>::s_object { nullptr };
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template<typename T>
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PerProcessData* PerProcess<T>::s_data { nullptr };
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} // namespace bmalloc
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