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 18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 19 # pragma GCC system_header 20 #endif 21 22 _LIBCPP_PUSH_MACROS 23 #include <__undef_macros> 24 25 _LIBCPP_BEGIN_NAMESPACE_STD 26 27 // Helper class to allocate memory using an Allocator in an exception safe 28 // manner. 29 // 30 // The intended usage of this class is as follows: 31 // 32 // 0 33 // 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 // 4 37 // 38 // If line (2) throws an exception during initialization of the memory, the 39 // guard's destructor will be called, and the memory will be released using 40 // Allocator deallocation. Otherwise, we release the memory from the guard on 41 // line (3) in an operation that can't throw -- after that, the guard is not 42 // responsible for the memory anymore. 43 // 44 // This is similar to a unique_ptr, except it's easier to use with a 45 // custom allocator. 46 template <class _Alloc> 47 struct __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 constructor 52 _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 important 56 {} 57 58 _LIBCPP_HIDE_FROM_ABI ~__allocation_guard() _NOEXCEPT { __destroy(); } 59 60 _LIBCPP_HIDE_FROM_ABI __allocation_guard(const __allocation_guard&) = delete; 61 _LIBCPP_HIDE_FROM_ABI __allocation_guard(__allocation_guard&& __other) _NOEXCEPT 62 : __alloc_(std::move(__other.__alloc_)), 63 __n_(__other.__n_), 64 __ptr_(__other.__ptr_) { 65 __other.__ptr_ = nullptr; 66 } 67 68 _LIBCPP_HIDE_FROM_ABI __allocation_guard& operator=(const __allocation_guard& __other) = delete; 69 _LIBCPP_HIDE_FROM_ABI __allocation_guard& operator=(__allocation_guard&& __other) _NOEXCEPT { 70 if (std::addressof(__other) != this) { 71 __destroy(); 72 73 __alloc_ = std::move(__other.__alloc_); 74 __n_ = __other.__n_; 75 __ptr_ = __other.__ptr_; 76 __other.__ptr_ = nullptr; 77 } 78 79 return *this; 80 } 81 82 _LIBCPP_HIDE_FROM_ABI _Pointer 83 __release_ptr() _NOEXCEPT { // not called __release() because it's a keyword in objective-c++ 84 _Pointer __tmp = __ptr_; 85 __ptr_ = nullptr; 86 return __tmp; 87 } 88 89 _LIBCPP_HIDE_FROM_ABI _Pointer __get() const _NOEXCEPT { return __ptr_; } 90 91 private: 92 _LIBCPP_HIDE_FROM_ABI void __destroy() _NOEXCEPT { 93 if (__ptr_ != nullptr) { 94 allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_, __n_); 95 } 96 } 97 98 _Alloc __alloc_; 99 _Size __n_; 100 _Pointer __ptr_; 101 }; 102 103 _LIBCPP_END_NAMESPACE_STD 104 105 _LIBCPP_POP_MACROS 106 107 #endif // _LIBCPP___MEMORY_ALLOCATION_GUARD_H 108