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/*
* Copyright (C) 2013 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. AND ITS CONTRIBUTORS ``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 ITS 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 NeverDestroyed_h
#define NeverDestroyed_h
#include <type_traits>
#include <utility>
#include <wtf/Noncopyable.h>
#include <wtf/RefCounted.h>
// NeverDestroyed is a smart pointer like class who ensures that the destructor
// for the given object is never called, but doesn't use the heap to allocate it.
// It's useful for static local variables, and can be used like so:
//
// MySharedGlobal& mySharedGlobal()
// {
// static NeverDestroyed<MySharedGlobal> myGlobal("Hello", 42);
// return myGlobal;
// }
namespace WTF {
template<typename T> class NeverDestroyed {
WTF_MAKE_NONCOPYABLE(NeverDestroyed);
public:
template<typename... Args>
NeverDestroyed(Args&&... args)
{
MaybeRelax<T>(new (asPtr()) T(std::forward<Args>(args)...));
}
operator T&() { return *asPtr(); }
T& get() { return *asPtr(); }
private:
typedef typename std::remove_const<T>::type* PointerType;
PointerType asPtr() { return reinterpret_cast<PointerType>(&m_storage); }
// FIXME: Investigate whether we should allocate a hunk of virtual memory
// and hand out chunks of it to NeverDestroyed instead, to reduce fragmentation.
typename std::aligned_storage<sizeof(T), std::alignment_of<T>::value>::type m_storage;
template <typename PtrType, bool ShouldRelax = std::is_base_of<RefCountedBase, PtrType>::value> struct MaybeRelax {
explicit MaybeRelax(PtrType*) { }
};
template <typename PtrType> struct MaybeRelax<PtrType, true> {
explicit MaybeRelax(PtrType* ptr) { ptr->relaxAdoptionRequirement(); }
};
};
template<typename T> class LazyNeverDestroyed {
WTF_MAKE_NONCOPYABLE(LazyNeverDestroyed);
public:
LazyNeverDestroyed() = default;
template<typename... Args>
void construct(Args&&... args)
{
ASSERT(!m_isConstructed);
#if !ASSERT_DISABLED
m_isConstructed = true;
#endif
MaybeRelax<T>(new (asPtr()) T(std::forward<Args>(args)...));
}
operator T&() { return *asPtr(); }
T& get() { return *asPtr(); }
T* operator->() { return asPtr(); }
private:
typedef typename std::remove_const<T>::type* PointerType;
PointerType asPtr()
{
ASSERT(m_isConstructed);
return reinterpret_cast<PointerType>(&m_storage);
}
// FIXME: Investigate whether we should allocate a hunk of virtual memory
// and hand out chunks of it to NeverDestroyed instead, to reduce fragmentation.
typename std::aligned_storage<sizeof(T), std::alignment_of<T>::value>::type m_storage;
template <typename PtrType, bool ShouldRelax = std::is_base_of<RefCountedBase, PtrType>::value> struct MaybeRelax {
explicit MaybeRelax(PtrType*) { }
};
template <typename PtrType> struct MaybeRelax<PtrType, true> {
explicit MaybeRelax(PtrType* ptr) { ptr->relaxAdoptionRequirement(); }
};
#if !ASSERT_DISABLED
// LazyNeverDestroyed objects are always static, so this variable is initialized to false.
// It must not be initialized dynamically, because that would not be thread safe.
bool m_isConstructed;
#endif
};
} // namespace WTF;
using WTF::LazyNeverDestroyed;
using WTF::NeverDestroyed;
#endif // NeverDestroyed_h
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