332da1c283
This has been broken out of D104170 since it should be merged whether or not we go ahead with the module map changes. Differential Revision: https://reviews.llvm.org/D104175
90 lines
2.7 KiB
C++
90 lines
2.7 KiB
C++
// -*- C++ -*-
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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___MEMORY_ALLOCATION_GUARD_H
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#define _LIBCPP___MEMORY_ALLOCATION_GUARD_H
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#include <__config>
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#include <__memory/allocator_traits.h>
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#include <cstddef>
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#include <utility>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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#pragma GCC system_header
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#endif
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_LIBCPP_PUSH_MACROS
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#include <__undef_macros>
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_LIBCPP_BEGIN_NAMESPACE_STD
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// Helper class to allocate memory using an Allocator in an exception safe
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// manner.
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//
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// The intended usage of this class is as follows:
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//
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// 0
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// 1 __allocation_guard<SomeAllocator> guard(alloc, 10);
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// 2 do_some_initialization_that_may_throw(guard.__get());
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// 3 save_allocated_pointer_in_a_noexcept_operation(guard.__release_ptr());
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// 4
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//
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// If line (2) throws an exception during initialization of the memory, the
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// guard's destructor will be called, and the memory will be released using
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// Allocator deallocation. Otherwise, we release the memory from the guard on
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// line (3) in an operation that can't throw -- after that, the guard is not
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// responsible for the memory anymore.
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//
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// This is similar to a unique_ptr, except it's easier to use with a
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// custom allocator.
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template<class _Alloc>
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struct __allocation_guard {
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using _Pointer = typename allocator_traits<_Alloc>::pointer;
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using _Size = typename allocator_traits<_Alloc>::size_type;
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template<class _AllocT> // we perform the allocator conversion inside the constructor
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_LIBCPP_HIDE_FROM_ABI
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explicit __allocation_guard(_AllocT __alloc, _Size __n)
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: __alloc_(_VSTD::move(__alloc))
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, __n_(__n)
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, __ptr_(allocator_traits<_Alloc>::allocate(__alloc_, __n_)) // initialization order is important
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{ }
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_LIBCPP_HIDE_FROM_ABI
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~__allocation_guard() _NOEXCEPT {
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if (__ptr_ != nullptr) {
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allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_, __n_);
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}
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}
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_LIBCPP_HIDE_FROM_ABI
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_Pointer __release_ptr() _NOEXCEPT { // not called __release() because it's a keyword in objective-c++
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_Pointer __tmp = __ptr_;
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__ptr_ = nullptr;
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return __tmp;
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}
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_LIBCPP_HIDE_FROM_ABI
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_Pointer __get() const _NOEXCEPT {
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return __ptr_;
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}
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private:
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_Alloc __alloc_;
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_Size __n_;
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_Pointer __ptr_;
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};
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_LIBCPP_END_NAMESPACE_STD
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_LIBCPP_POP_MACROS
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#endif // _LIBCPP___MEMORY_ALLOCATION_GUARD_H
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