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1// -*- C++ -*-2//===----------------------------------------------------------------------===//3//4// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.5// See https://llvm.org/LICENSE.txt for license information.6// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception7//8//===----------------------------------------------------------------------===//9 10#ifndef _LIBCPP___MEMORY_ALLOCATION_GUARD_H11#define _LIBCPP___MEMORY_ALLOCATION_GUARD_H12 13#include <__config>14#include <__memory/addressof.h>15#include <__memory/allocator_traits.h>16#include <__utility/move.h>17 18#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)19# pragma GCC system_header20#endif21 22_LIBCPP_PUSH_MACROS23#include <__undef_macros>24 25_LIBCPP_BEGIN_NAMESPACE_STD26 27// Helper class to allocate memory using an Allocator in an exception safe28// manner.29//30// The intended usage of this class is as follows:31//32// 033// 1 __allocation_guard<SomeAllocator> guard(alloc, 10);34// 2 do_some_initialization_that_may_throw(guard.__get());35// 3 save_allocated_pointer_in_a_noexcept_operation(guard.__release_ptr());36// 437//38// If line (2) throws an exception during initialization of the memory, the39// guard's destructor will be called, and the memory will be released using40// Allocator deallocation. Otherwise, we release the memory from the guard on41// line (3) in an operation that can't throw -- after that, the guard is not42// responsible for the memory anymore.43//44// This is similar to a unique_ptr, except it's easier to use with a45// custom allocator.46template <class _Alloc>47struct __allocation_guard {48 using _Pointer _LIBCPP_NODEBUG = typename allocator_traits<_Alloc>::pointer;49 using _Size _LIBCPP_NODEBUG = typename allocator_traits<_Alloc>::size_type;50 51 template <class _AllocT> // we perform the allocator conversion inside the constructor52 _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI explicit __allocation_guard(_AllocT __alloc, _Size __n)53 : __alloc_(std::move(__alloc)),54 __n_(__n),55 __ptr_(allocator_traits<_Alloc>::allocate(__alloc_, __n_)) // initialization order is important56 {}57 58 _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI ~__allocation_guard() _NOEXCEPT { __destroy(); }59 60 __allocation_guard(const __allocation_guard&) = delete;61 __allocation_guard& operator=(const __allocation_guard& __other) = delete;62 63 _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI __allocation_guard(__allocation_guard&& __other) _NOEXCEPT64 : __alloc_(std::move(__other.__alloc_)),65 __n_(__other.__n_),66 __ptr_(__other.__ptr_) {67 __other.__ptr_ = nullptr;68 }69 70 _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI __allocation_guard&71 operator=(__allocation_guard&& __other) _NOEXCEPT {72 if (std::addressof(__other) != this) {73 __destroy();74 75 __alloc_ = std::move(__other.__alloc_);76 __n_ = __other.__n_;77 __ptr_ = __other.__ptr_;78 __other.__ptr_ = nullptr;79 }80 81 return *this;82 }83 84 _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI _Pointer85 __release_ptr() _NOEXCEPT { // not called __release() because it's a keyword in objective-c++86 _Pointer __tmp = __ptr_;87 __ptr_ = nullptr;88 return __tmp;89 }90 91 _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI _Pointer __get() const _NOEXCEPT { return __ptr_; }92 93private:94 _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI void __destroy() _NOEXCEPT {95 if (__ptr_ != nullptr) {96 allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_, __n_);97 }98 }99 100 _Alloc __alloc_;101 _Size __n_;102 _Pointer __ptr_;103};104 105_LIBCPP_END_NAMESPACE_STD106 107_LIBCPP_POP_MACROS108 109#endif // _LIBCPP___MEMORY_ALLOCATION_GUARD_H110