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 #include <utility> 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 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 if (__ptr_ != nullptr) { 63 allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_, __n_); 64 } 65 } 66 67 _LIBCPP_HIDE_FROM_ABI 68 _Pointer __release_ptr() _NOEXCEPT { // not called __release() because it's a keyword in objective-c++ 69 _Pointer __tmp = __ptr_; 70 __ptr_ = nullptr; 71 return __tmp; 72 } 73 74 _LIBCPP_HIDE_FROM_ABI 75 _Pointer __get() const _NOEXCEPT { 76 return __ptr_; 77 } 78 79 private: 80 _Alloc __alloc_; 81 _Size __n_; 82 _Pointer __ptr_; 83 }; 84 85 _LIBCPP_END_NAMESPACE_STD 86 87 _LIBCPP_POP_MACROS 88 89 #endif // _LIBCPP___MEMORY_ALLOCATION_GUARD_H 90