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 <__utility/move.h> 16 #include <cstddef> 17 18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 19 # pragma GCC system_header 20 #endif 21 22 _LIBCPP_BEGIN_NAMESPACE_STD 23 24 // Helper class to allocate memory using an Allocator in an exception safe 25 // manner. 26 // 27 // The intended usage of this class is as follows: 28 // 29 // 0 30 // 1 __allocation_guard<SomeAllocator> guard(alloc, 10); 31 // 2 do_some_initialization_that_may_throw(guard.__get()); 32 // 3 save_allocated_pointer_in_a_noexcept_operation(guard.__release_ptr()); 33 // 4 34 // 35 // If line (2) throws an exception during initialization of the memory, the 36 // guard's destructor will be called, and the memory will be released using 37 // Allocator deallocation. Otherwise, we release the memory from the guard on 38 // line (3) in an operation that can't throw -- after that, the guard is not 39 // responsible for the memory anymore. 40 // 41 // This is similar to a unique_ptr, except it's easier to use with a 42 // custom allocator. 43 template<class _Alloc> 44 struct __allocation_guard { 45 using _Pointer = typename allocator_traits<_Alloc>::pointer; 46 using _Size = typename allocator_traits<_Alloc>::size_type; 47 48 template<class _AllocT> // we perform the allocator conversion inside the constructor 49 _LIBCPP_HIDE_FROM_ABI 50 explicit __allocation_guard(_AllocT __alloc, _Size __n) 51 : __alloc_(_VSTD::move(__alloc)) 52 , __n_(__n) 53 , __ptr_(allocator_traits<_Alloc>::allocate(__alloc_, __n_)) // initialization order is important 54 { } 55 56 _LIBCPP_HIDE_FROM_ABI 57 ~__allocation_guard() _NOEXCEPT { 58 if (__ptr_ != nullptr) { 59 allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_, __n_); 60 } 61 } 62 63 _LIBCPP_HIDE_FROM_ABI 64 _Pointer __release_ptr() _NOEXCEPT { // not called __release() because it's a keyword in objective-c++ 65 _Pointer __tmp = __ptr_; 66 __ptr_ = nullptr; 67 return __tmp; 68 } 69 70 _LIBCPP_HIDE_FROM_ABI 71 _Pointer __get() const _NOEXCEPT { 72 return __ptr_; 73 } 74 75 private: 76 _Alloc __alloc_; 77 _Size __n_; 78 _Pointer __ptr_; 79 }; 80 81 _LIBCPP_END_NAMESPACE_STD 82 83 #endif // _LIBCPP___MEMORY_ALLOCATION_GUARD_H 84