[libcxx-commits] [libcxx] 19d57b5 - [libc++] Refactor allocate_shared to use an allocation guard
Louis Dionne via libcxx-commits
libcxx-commits at lists.llvm.org
Mon Dec 14 14:10:30 PST 2020
Author: Louis Dionne
Date: 2020-12-14T17:10:05-05:00
New Revision: 19d57b5c42b4e80fcbd5b6a2167e4a5f4f7b64c3
URL: https://github.com/llvm/llvm-project/commit/19d57b5c42b4e80fcbd5b6a2167e4a5f4f7b64c3
DIFF: https://github.com/llvm/llvm-project/commit/19d57b5c42b4e80fcbd5b6a2167e4a5f4f7b64c3.diff
LOG: [libc++] Refactor allocate_shared to use an allocation guard
This commit is a step towards making it easier to add support for arrays
in allocate_shared. Adding support for arrays will require writing multiple
functions, and the current complexity of writing allocate_shared is
prohibitive for understanding.
Differential Revision: https://reviews.llvm.org/D93130
Added:
libcxx/include/__memory/utilities.h
Modified:
libcxx/include/CMakeLists.txt
libcxx/include/memory
Removed:
################################################################################
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index 71361a9e53df..cd12f60a049c 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -14,6 +14,7 @@ set(files
__memory/allocator_traits.h
__memory/base.h
__memory/pointer_traits.h
+ __memory/utilities.h
__mutex_base
__node_handle
__nullptr
diff --git a/libcxx/include/__memory/utilities.h b/libcxx/include/__memory/utilities.h
new file mode 100644
index 000000000000..ccbfbe78966c
--- /dev/null
+++ b/libcxx/include/__memory/utilities.h
@@ -0,0 +1,87 @@
+// -*- 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_UTILITIES_H
+#define _LIBCPP___MEMORY_UTILITIES_H
+
+#include <__config>
+#include <__memory/allocator_traits.h>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+
+_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;
+
+ _LIBCPP_HIDE_FROM_ABI
+ explicit __allocation_guard(_Alloc __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
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___MEMORY_UTILITIES_H
diff --git a/libcxx/include/memory b/libcxx/include/memory
index f81ff6680f9f..24ad9e567b99 100644
--- a/libcxx/include/memory
+++ b/libcxx/include/memory
@@ -682,6 +682,7 @@ void* align(size_t alignment, size_t size, void*& ptr, size_t& space);
#include <__memory/allocator_traits.h>
#include <__memory/base.h>
#include <__memory/pointer_traits.h>
+#include <__memory/utilities.h>
#if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER)
# include <atomic>
#endif
@@ -3299,28 +3300,21 @@ shared_ptr<_Tp>::reset(_Yp* __p, _Dp __d, _Alloc __a)
shared_ptr(__p, __d, __a).swap(*this);
}
-template<class _Tp, class _Alloc, class ..._Args>
-inline _LIBCPP_INLINE_VISIBILITY
-typename enable_if
-<
- !is_array<_Tp>::value,
- shared_ptr<_Tp>
->::type
-allocate_shared(const _Alloc& __a, _Args&& ...__args)
+//
+// std::allocate_shared and std::make_shared
+//
+template<class _Tp, class _Alloc, class ..._Args, class = _EnableIf<!is_array<_Tp>::value> >
+_LIBCPP_HIDE_FROM_ABI
+shared_ptr<_Tp> allocate_shared(const _Alloc& __a, _Args&& ...__args)
{
static_assert(is_constructible<_Tp, _Args...>::value,
"allocate_shared/make_shared: the type is not constructible from the provided arguments");
-
- typedef __shared_ptr_emplace<_Tp, _Alloc> _CntrlBlk;
- typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
- typedef __allocator_destructor<_A2> _D2;
-
- _A2 __a2(__a);
- unique_ptr<_CntrlBlk, _D2> __hold2(__a2.allocate(1), _D2(__a2, 1));
- ::new ((void*)_VSTD::addressof(*__hold2.get())) _CntrlBlk(__a, _VSTD::forward<_Args>(__args)...);
-
- typename shared_ptr<_Tp>::element_type *__p = __hold2->__get_elem();
- return shared_ptr<_Tp>::__create_with_control_block(__p, _VSTD::addressof(*__hold2.release()));
+ using _ControlBlock = __shared_ptr_emplace<_Tp, _Alloc>;
+ using _ControlBlockAllocator = typename __allocator_traits_rebind<_Alloc, _ControlBlock>::type;
+ __allocation_guard<_ControlBlockAllocator> __guard(__a, 1);
+ ::new ((void*)_VSTD::addressof(*__guard.__get())) _ControlBlock(__a, _VSTD::forward<_Args>(__args)...);
+ auto __control_block = __guard.__release_ptr();
+ return shared_ptr<_Tp>::__create_with_control_block((*__control_block).__get_elem(), _VSTD::addressof(*__control_block));
}
template<class _Tp, class ..._Args, class = _EnableIf<!is_array<_Tp>::value> >
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