| // -*- C++ -*- |
| //===----------------------------------------------------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef _LIBCPP___MEMORY_ALLOCATION_GUARD_H |
| #define _LIBCPP___MEMORY_ALLOCATION_GUARD_H |
| |
| #include <__config> |
| #include <__memory/allocator_traits.h> |
| #include <cstddef> |
| #include <utility> |
| |
| #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) |
| #pragma GCC system_header |
| #endif |
| |
| _LIBCPP_BEGIN_NAMESPACE_STD |
| |
| // Helper class to allocate memory using an Allocator in an exception safe |
| // manner. |
| // |
| // The intended usage of this class is as follows: |
| // |
| // 0 |
| // 1 __allocation_guard<SomeAllocator> guard(alloc, 10); |
| // 2 do_some_initialization_that_may_throw(guard.__get()); |
| // 3 save_allocated_pointer_in_a_noexcept_operation(guard.__release_ptr()); |
| // 4 |
| // |
| // If line (2) throws an exception during initialization of the memory, the |
| // guard's destructor will be called, and the memory will be released using |
| // Allocator deallocation. Otherwise, we release the memory from the guard on |
| // line (3) in an operation that can't throw -- after that, the guard is not |
| // responsible for the memory anymore. |
| // |
| // This is similar to a unique_ptr, except it's easier to use with a |
| // custom allocator. |
| template<class _Alloc> |
| struct __allocation_guard { |
| using _Pointer = typename allocator_traits<_Alloc>::pointer; |
| using _Size = typename allocator_traits<_Alloc>::size_type; |
| |
| template<class _AllocT> // we perform the allocator conversion inside the constructor |
| _LIBCPP_HIDE_FROM_ABI |
| explicit __allocation_guard(_AllocT __alloc, _Size __n) |
| : __alloc_(_VSTD::move(__alloc)) |
| , __n_(__n) |
| , __ptr_(allocator_traits<_Alloc>::allocate(__alloc_, __n_)) // initialization order is important |
| { } |
| |
| _LIBCPP_HIDE_FROM_ABI |
| ~__allocation_guard() _NOEXCEPT { |
| if (__ptr_ != nullptr) { |
| allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_, __n_); |
| } |
| } |
| |
| _LIBCPP_HIDE_FROM_ABI |
| _Pointer __release_ptr() _NOEXCEPT { // not called __release() because it's a keyword in objective-c++ |
| _Pointer __tmp = __ptr_; |
| __ptr_ = nullptr; |
| return __tmp; |
| } |
| |
| _LIBCPP_HIDE_FROM_ABI |
| _Pointer __get() const _NOEXCEPT { |
| return __ptr_; |
| } |
| |
| private: |
| _Alloc __alloc_; |
| _Size __n_; |
| _Pointer __ptr_; |
| }; |
| |
| _LIBCPP_END_NAMESPACE_STD |
| |
| #endif // _LIBCPP___MEMORY_ALLOCATION_GUARD_H |