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74 lines
2.2 KiB
C++
74 lines
2.2 KiB
C++
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// ManualConstructor statically-allocates space in which to store some
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// object, but does not initialize it. You can then call the constructor
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// and destructor for the object yourself as you see fit. This is useful
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// for memory management optimizations, where you want to initialize and
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// destroy an object multiple times but only allocate it once.
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//
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// (When I say ManualConstructor statically allocates space, I mean that
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// the ManualConstructor object itself is forced to be the right size.)
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//
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// For example usage, check out base/containers/small_map.h.
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#ifndef BASE_MEMORY_MANUAL_CONSTRUCTOR_H_
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#define BASE_MEMORY_MANUAL_CONSTRUCTOR_H_
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#include <stddef.h>
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#include "base/compiler_specific.h"
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#include "base/memory/aligned_memory.h"
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namespace base {
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template <typename Type>
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class ManualConstructor {
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public:
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// No constructor or destructor because one of the most useful uses of
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// this class is as part of a union, and members of a union cannot have
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// constructors or destructors. And, anyway, the whole point of this
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// class is to bypass these.
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// Support users creating arrays of ManualConstructor<>s. This ensures that
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// the array itself has the correct alignment.
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static void* operator new[](size_t size) {
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return AlignedAlloc(size, alignof(Type));
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}
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static void operator delete[](void* mem) {
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AlignedFree(mem);
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}
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inline Type* get() { return reinterpret_cast<Type*>(space_); }
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inline const Type* get() const {
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return reinterpret_cast<const Type*>(space_);
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}
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inline Type* operator->() { return get(); }
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inline const Type* operator->() const { return get(); }
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inline Type& operator*() { return *get(); }
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inline const Type& operator*() const { return *get(); }
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template <typename... Ts>
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inline void Init(Ts&&... params) {
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new (space_) Type(std::forward<Ts>(params)...);
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}
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inline void InitFromMove(ManualConstructor<Type>&& o) {
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Init(std::move(*o));
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}
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inline void Destroy() {
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get()->~Type();
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}
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private:
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alignas(Type) char space_[sizeof(Type)];
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};
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} // namespace base
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#endif // BASE_MEMORY_MANUAL_CONSTRUCTOR_H_
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