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-exception 7 // 8 //===----------------------------------------------------------------------===// 9 10 #ifndef _LIBCPP___MEMORY_ALLOCATION_GUARD_H 11 #define _LIBCPP___MEMORY_ALLOCATION_GUARD_H 12 13 #include <__config> 14 #include <__memory/addressof.h> 15 #include <__memory/allocator_traits.h> 16 #include <__utility/move.h> 17 #include <cstddef> 18 19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 20 # pragma GCC system_header 21 #endif 22 23 _LIBCPP_PUSH_MACROS 24 #include <__undef_macros> 25 26 _LIBCPP_BEGIN_NAMESPACE_STD 27 28 // Helper class to allocate memory using an Allocator in an exception safe 29 // manner. 30 // 31 // The intended usage of this class is as follows: 32 // 33 // 0 34 // 1 __allocation_guard<SomeAllocator> guard(alloc, 10); 35 // 2 do_some_initialization_that_may_throw(guard.__get()); 36 // 3 save_allocated_pointer_in_a_noexcept_operation(guard.__release_ptr()); 37 // 4 38 // 39 // If line (2) throws an exception during initialization of the memory, the 40 // guard's destructor will be called, and the memory will be released using 41 // Allocator deallocation. Otherwise, we release the memory from the guard on 42 // line (3) in an operation that can't throw -- after that, the guard is not 43 // responsible for the memory anymore. 44 // 45 // This is similar to a unique_ptr, except it's easier to use with a 46 // custom allocator. 47 template<class _Alloc> 48 struct __allocation_guard { 49 using _Pointer = typename allocator_traits<_Alloc>::pointer; 50 using _Size = typename allocator_traits<_Alloc>::size_type; 51 52 template<class _AllocT> // we perform the allocator conversion inside the constructor 53 _LIBCPP_HIDE_FROM_ABI 54 explicit __allocation_guard(_AllocT __alloc, _Size __n) 55 : __alloc_(_VSTD::move(__alloc)) 56 , __n_(__n) 57 , __ptr_(allocator_traits<_Alloc>::allocate(__alloc_, __n_)) // initialization order is important 58 { } 59 60 _LIBCPP_HIDE_FROM_ABI 61 ~__allocation_guard() _NOEXCEPT { 62 __destroy(); 63 } 64 65 _LIBCPP_HIDE_FROM_ABI __allocation_guard(const __allocation_guard&) = delete; 66 _LIBCPP_HIDE_FROM_ABI __allocation_guard(__allocation_guard&& __other) _NOEXCEPT 67 : __alloc_(std::move(__other.__alloc_)) 68 , __n_(__other.__n_) 69 , __ptr_(__other.__ptr_) { 70 __other.__ptr_ = nullptr; 71 } 72 73 _LIBCPP_HIDE_FROM_ABI __allocation_guard& operator=(const __allocation_guard& __other) = delete; 74 _LIBCPP_HIDE_FROM_ABI __allocation_guard& operator=(__allocation_guard&& __other) _NOEXCEPT { 75 if (std::addressof(__other) != this) { 76 __destroy(); 77 78 __alloc_ = std::move(__other.__alloc_); 79 __n_ = __other.__n_; 80 __ptr_ = __other.__ptr_; 81 __other.__ptr_ = nullptr; 82 } 83 84 return *this; 85 } 86 87 _LIBCPP_HIDE_FROM_ABI 88 _Pointer __release_ptr() _NOEXCEPT { // not called __release() because it's a keyword in objective-c++ 89 _Pointer __tmp = __ptr_; 90 __ptr_ = nullptr; 91 return __tmp; 92 } 93 94 _LIBCPP_HIDE_FROM_ABI 95 _Pointer __get() const _NOEXCEPT { 96 return __ptr_; 97 } 98 99 private: 100 _LIBCPP_HIDE_FROM_ABI 101 void __destroy() _NOEXCEPT { 102 if (__ptr_ != nullptr) { 103 allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_, __n_); 104 } 105 } 106 107 _Alloc __alloc_; 108 _Size __n_; 109 _Pointer __ptr_; 110 }; 111 112 _LIBCPP_END_NAMESPACE_STD 113 114 _LIBCPP_POP_MACROS 115 116 #endif // _LIBCPP___MEMORY_ALLOCATION_GUARD_H 117