368faacac7
This commit reverts 5aaefa51 (and also partly 7f285f48e77 and b6d75682f9, which were related to the original commit). As landed, 5aaefa51 had unintended consequences on some downstream bots and didn't have proper coverage upstream due to a few subtle things. Implementing this is something we should do in libc++, however we'll first need to address a few issues listed in https://reviews.llvm.org/D106124#3349710. Differential Revision: https://reviews.llvm.org/D120683
84 lines
2.6 KiB
C++
84 lines
2.6 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 <__utility/move.h>
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#include <cstddef>
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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_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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#endif // _LIBCPP___MEMORY_ALLOCATION_GUARD_H
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