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110 lines (93 loc) · 3.27 KB
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/*
* 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 (gobalFlag) { ... } // Undefined behavior.
//
// std::lock_guard<StaticMutex> lock(PerProcess<Object>::mutex());
// Object* object = PerProcess<Object>::get(lock);
// if (gobalFlag) { ... } // 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