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 explicit __allocation_guard(_AllocT __alloc, _Size __n) 54 : __alloc_(std::move(__alloc)), 55 __n_(__n), 56 __ptr_(allocator_traits<_Alloc>::allocate(__alloc_, __n_)) // initialization order is important 57 {} 58 59 _LIBCPP_HIDE_FROM_ABI ~__allocation_guard() _NOEXCEPT { __destroy(); } 60 61 _LIBCPP_HIDE_FROM_ABI __allocation_guard(const __allocation_guard&) = delete; 62 _LIBCPP_HIDE_FROM_ABI __allocation_guard(__allocation_guard&& __other) _NOEXCEPT 63 : __alloc_(std::move(__other.__alloc_)), 64 __n_(__other.__n_), 65 __ptr_(__other.__ptr_) { 66 __other.__ptr_ = nullptr; 67 } 68 69 _LIBCPP_HIDE_FROM_ABI __allocation_guard& operator=(const __allocation_guard& __other) = delete; 70 _LIBCPP_HIDE_FROM_ABI __allocation_guard& operator=(__allocation_guard&& __other) _NOEXCEPT { 71 if (std::addressof(__other) != this) { 72 __destroy(); 73 74 __alloc_ = std::move(__other.__alloc_); 75 __n_ = __other.__n_; 76 __ptr_ = __other.__ptr_; 77 __other.__ptr_ = nullptr; 78 } 79 80 return *this; 81 } 82 83 _LIBCPP_HIDE_FROM_ABI _Pointer 84 __release_ptr() _NOEXCEPT { // not called __release() because it's a keyword in objective-c++ 85 _Pointer __tmp = __ptr_; 86 __ptr_ = nullptr; 87 return __tmp; 88 } 89 90 _LIBCPP_HIDE_FROM_ABI _Pointer __get() const _NOEXCEPT { return __ptr_; } 91 92 private: 93 _LIBCPP_HIDE_FROM_ABI void __destroy() _NOEXCEPT { 94 if (__ptr_ != nullptr) { 95 allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_, __n_); 96 } 97 } 98 99 _Alloc __alloc_; 100 _Size __n_; 101 _Pointer __ptr_; 102 }; 103 104 _LIBCPP_END_NAMESPACE_STD 105 106 _LIBCPP_POP_MACROS 107 108 #endif // _LIBCPP___MEMORY_ALLOCATION_GUARD_H 109