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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-exception7//8//===----------------------------------------------------------------------===//9 10#ifndef _LIBCPP___STOP_TOKEN_INTRUSIVE_SHARED_PTR_H11#define _LIBCPP___STOP_TOKEN_INTRUSIVE_SHARED_PTR_H12 13#include <__atomic/atomic.h>14#include <__atomic/memory_order.h>15#include <__config>16#include <__cstddef/nullptr_t.h>17#include <__memory/addressof.h>18#include <__type_traits/is_reference.h>19#include <__utility/move.h>20#include <__utility/swap.h>21 22#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)23# pragma GCC system_header24#endif25 26_LIBCPP_PUSH_MACROS27#include <__undef_macros>28 29_LIBCPP_BEGIN_NAMESPACE_STD30 31#if _LIBCPP_STD_VER >= 2032 33// For intrusive_shared_ptr to work with a type T, specialize __intrusive_shared_ptr_traits<T> and implement34// the following function:35//36// static std::atomic<U>& __get_atomic_ref_count(T&);37//38// where U must be an integral type representing the number of references to the object.39template <class _Tp>40struct __intrusive_shared_ptr_traits;41 42// A reference counting shared_ptr for types whose reference counter43// is stored inside the class _Tp itself.44// When the reference count goes to zero, the destructor of _Tp will be called45template <class _Tp>46struct __intrusive_shared_ptr {47 _LIBCPP_HIDE_FROM_ABI __intrusive_shared_ptr() = default;48 49 _LIBCPP_HIDE_FROM_ABI explicit __intrusive_shared_ptr(_Tp* __raw_ptr) : __raw_ptr_(__raw_ptr) {50 if (__raw_ptr_)51 __increment_ref_count(*__raw_ptr_);52 }53 54 _LIBCPP_HIDE_FROM_ABI __intrusive_shared_ptr(const __intrusive_shared_ptr& __other) noexcept55 : __raw_ptr_(__other.__raw_ptr_) {56 if (__raw_ptr_)57 __increment_ref_count(*__raw_ptr_);58 }59 60 _LIBCPP_HIDE_FROM_ABI __intrusive_shared_ptr(__intrusive_shared_ptr&& __other) noexcept61 : __raw_ptr_(__other.__raw_ptr_) {62 __other.__raw_ptr_ = nullptr;63 }64 65 _LIBCPP_HIDE_FROM_ABI __intrusive_shared_ptr& operator=(const __intrusive_shared_ptr& __other) noexcept {66 if (__other.__raw_ptr_ != __raw_ptr_) {67 if (__other.__raw_ptr_) {68 __increment_ref_count(*__other.__raw_ptr_);69 }70 if (__raw_ptr_) {71 __decrement_ref_count(*__raw_ptr_);72 }73 __raw_ptr_ = __other.__raw_ptr_;74 }75 return *this;76 }77 78 _LIBCPP_HIDE_FROM_ABI __intrusive_shared_ptr& operator=(__intrusive_shared_ptr&& __other) noexcept {79 __intrusive_shared_ptr(std::move(__other)).swap(*this);80 return *this;81 }82 83 _LIBCPP_HIDE_FROM_ABI ~__intrusive_shared_ptr() {84 if (__raw_ptr_) {85 __decrement_ref_count(*__raw_ptr_);86 }87 }88 89 _LIBCPP_HIDE_FROM_ABI _Tp* operator->() const noexcept { return __raw_ptr_; }90 _LIBCPP_HIDE_FROM_ABI _Tp& operator*() const noexcept { return *__raw_ptr_; }91 _LIBCPP_HIDE_FROM_ABI explicit operator bool() const noexcept { return __raw_ptr_ != nullptr; }92 93 _LIBCPP_HIDE_FROM_ABI void swap(__intrusive_shared_ptr& __other) { std::swap(__raw_ptr_, __other.__raw_ptr_); }94 95 _LIBCPP_HIDE_FROM_ABI friend void swap(__intrusive_shared_ptr& __lhs, __intrusive_shared_ptr& __rhs) {96 __lhs.swap(__rhs);97 }98 99 _LIBCPP_HIDE_FROM_ABI friend bool constexpr100 operator==(const __intrusive_shared_ptr&, const __intrusive_shared_ptr&) = default;101 102 _LIBCPP_HIDE_FROM_ABI friend bool constexpr operator==(const __intrusive_shared_ptr& __ptr, std::nullptr_t) {103 return __ptr.__raw_ptr_ == nullptr;104 }105 106private:107 _Tp* __raw_ptr_ = nullptr;108 109 // the memory order for increment/decrement the counter is the same for shared_ptr110 // increment is relaxed and decrement is acq_rel111 _LIBCPP_HIDE_FROM_ABI static void __increment_ref_count(_Tp& __obj) {112 __get_atomic_ref_count(__obj).fetch_add(1, std::memory_order_relaxed);113 }114 115 _LIBCPP_HIDE_FROM_ABI static void __decrement_ref_count(_Tp& __obj) {116 if (__get_atomic_ref_count(__obj).fetch_sub(1, std::memory_order_acq_rel) == 1) {117 delete std::addressof(__obj);118 }119 }120 121 _LIBCPP_HIDE_FROM_ABI static decltype(auto) __get_atomic_ref_count(_Tp& __obj) {122 using __ret_type = decltype(__intrusive_shared_ptr_traits<_Tp>::__get_atomic_ref_count(__obj));123 static_assert(124 std::is_reference_v<__ret_type>, "__get_atomic_ref_count should return a reference to the atomic counter");125 return __intrusive_shared_ptr_traits<_Tp>::__get_atomic_ref_count(__obj);126 }127};128 129#endif // _LIBCPP_STD_VER >= 20130 131_LIBCPP_END_NAMESPACE_STD132 133_LIBCPP_POP_MACROS134 135#endif // _LIBCPP___STOP_TOKEN_INTRUSIVE_SHARED_PTR_H136