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/allocator_traits.h> 15 #include <cstddef> 16 17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 18 #pragma GCC system_header 19 #endif 20 21 _LIBCPP_PUSH_MACROS 22 #include <__undef_macros> 23 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 = typename allocator_traits<_Alloc>::pointer; 49 using _Size = typename allocator_traits<_Alloc>::size_type; 50 51 template<class _AllocT> // we perform the allocator conversion inside the constructor 52 _LIBCPP_HIDE_FROM_ABI __allocation_guard__allocation_guard53 explicit __allocation_guard(_AllocT __alloc, _Size __n) 54 : __alloc_(_VSTD::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__allocation_guard60 ~__allocation_guard() _NOEXCEPT { 61 if (__ptr_ != nullptr) { 62 allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_, __n_); 63 } 64 } 65 66 _LIBCPP_HIDE_FROM_ABI __release_ptr__allocation_guard67 _Pointer __release_ptr() _NOEXCEPT { // not called __release() because it's a keyword in objective-c++ 68 _Pointer __tmp = __ptr_; 69 __ptr_ = nullptr; 70 return __tmp; 71 } 72 73 _LIBCPP_HIDE_FROM_ABI __get__allocation_guard74 _Pointer __get() const _NOEXCEPT { 75 return __ptr_; 76 } 77 78 private: 79 _Alloc __alloc_; 80 _Size __n_; 81 _Pointer __ptr_; 82 }; 83 84 _LIBCPP_END_NAMESPACE_STD 85 86 _LIBCPP_POP_MACROS 87 88 #endif // _LIBCPP___MEMORY_ALLOCATION_GUARD_H 89