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-exception
7//
8//===----------------------------------------------------------------------===//
9
10#ifndef _LIBCPP___STOP_TOKEN_INTRUSIVE_SHARED_PTR_H
11#define _LIBCPP___STOP_TOKEN_INTRUSIVE_SHARED_PTR_H
12
13#include <__atomic/memory_order.h>
14#include <__config>
15#include <__cstddef/nullptr_t.h>
16#include <__memory/addressof.h>
17#include <__type_traits/is_reference.h>
18#include <__utility/move.h>
19#include <__utility/swap.h>
20
21#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
22# pragma GCC system_header
23#endif
24
25_LIBCPP_PUSH_MACROS
26#include <__undef_macros>
27
28#if _LIBCPP_STD_VER >= 20
29
30_LIBCPP_BEGIN_NAMESPACE_STD
31
32// For intrusive_shared_ptr to work with a type T, specialize __intrusive_shared_ptr_traits<T> and implement
33// the following function:
34//
35// static std::atomic<U>& __get_atomic_ref_count(T&);
36//
37// where U must be an integral type representing the number of references to the object.
38template <class _Tp>
39struct __intrusive_shared_ptr_traits;
40
41// A reference counting shared_ptr for types whose reference counter
42// is stored inside the class _Tp itself.
43// When the reference count goes to zero, the destructor of _Tp will be called
44template <class _Tp>
45struct __intrusive_shared_ptr {
46 _LIBCPP_HIDE_FROM_ABI __intrusive_shared_ptr() = default;
47
48 _LIBCPP_HIDE_FROM_ABI explicit __intrusive_shared_ptr(_Tp* __raw_ptr) : __raw_ptr_(__raw_ptr) {
49 if (__raw_ptr_)
50 __increment_ref_count(obj&: *__raw_ptr_);
51 }
52
53 _LIBCPP_HIDE_FROM_ABI __intrusive_shared_ptr(const __intrusive_shared_ptr& __other) noexcept
54 : __raw_ptr_(__other.__raw_ptr_) {
55 if (__raw_ptr_)
56 __increment_ref_count(obj&: *__raw_ptr_);
57 }
58
59 _LIBCPP_HIDE_FROM_ABI __intrusive_shared_ptr(__intrusive_shared_ptr&& __other) noexcept
60 : __raw_ptr_(__other.__raw_ptr_) {
61 __other.__raw_ptr_ = nullptr;
62 }
63
64 _LIBCPP_HIDE_FROM_ABI __intrusive_shared_ptr& operator=(const __intrusive_shared_ptr& __other) noexcept {
65 if (__other.__raw_ptr_ != __raw_ptr_) {
66 if (__other.__raw_ptr_) {
67 __increment_ref_count(obj&: *__other.__raw_ptr_);
68 }
69 if (__raw_ptr_) {
70 __decrement_ref_count(obj&: *__raw_ptr_);
71 }
72 __raw_ptr_ = __other.__raw_ptr_;
73 }
74 return *this;
75 }
76
77 _LIBCPP_HIDE_FROM_ABI __intrusive_shared_ptr& operator=(__intrusive_shared_ptr&& __other) noexcept {
78 __intrusive_shared_ptr(std::move(__other)).swap(other&: *this);
79 return *this;
80 }
81
82 _LIBCPP_HIDE_FROM_ABI ~__intrusive_shared_ptr() {
83 if (__raw_ptr_) {
84 __decrement_ref_count(obj&: *__raw_ptr_);
85 }
86 }
87
88 _LIBCPP_HIDE_FROM_ABI _Tp* operator->() const noexcept { return __raw_ptr_; }
89 _LIBCPP_HIDE_FROM_ABI _Tp& operator*() const noexcept { return *__raw_ptr_; }
90 _LIBCPP_HIDE_FROM_ABI explicit operator bool() const noexcept { return __raw_ptr_ != nullptr; }
91
92 _LIBCPP_HIDE_FROM_ABI void swap(__intrusive_shared_ptr& __other) { std::swap(__raw_ptr_, __other.__raw_ptr_); }
93
94 _LIBCPP_HIDE_FROM_ABI friend void swap(__intrusive_shared_ptr& __lhs, __intrusive_shared_ptr& __rhs) {
95 __lhs.swap(other&: __rhs);
96 }
97
98 _LIBCPP_HIDE_FROM_ABI friend bool constexpr
99 operator==(const __intrusive_shared_ptr&, const __intrusive_shared_ptr&) = default;
100
101 _LIBCPP_HIDE_FROM_ABI friend bool constexpr operator==(const __intrusive_shared_ptr& __ptr, std::nullptr_t) {
102 return __ptr.__raw_ptr_ == nullptr;
103 }
104
105private:
106 _Tp* __raw_ptr_ = nullptr;
107
108 // the memory order for increment/decrement the counter is the same for shared_ptr
109 // increment is relaxed and decrement is acq_rel
110 _LIBCPP_HIDE_FROM_ABI static void __increment_ref_count(_Tp& __obj) {
111 __get_atomic_ref_count(__obj).fetch_add(1, std::memory_order_relaxed);
112 }
113
114 _LIBCPP_HIDE_FROM_ABI static void __decrement_ref_count(_Tp& __obj) {
115 if (__get_atomic_ref_count(__obj).fetch_sub(1, std::memory_order_acq_rel) == 1) {
116 delete std::addressof(__obj);
117 }
118 }
119
120 _LIBCPP_HIDE_FROM_ABI static decltype(auto) __get_atomic_ref_count(_Tp& __obj) {
121 using __ret_type = decltype(__intrusive_shared_ptr_traits<_Tp>::__get_atomic_ref_count(__obj));
122 static_assert(
123 std::is_reference_v<__ret_type>, "__get_atomic_ref_count should return a reference to the atomic counter");
124 return __intrusive_shared_ptr_traits<_Tp>::__get_atomic_ref_count(__obj);
125 }
126};
127
128_LIBCPP_END_NAMESPACE_STD
129
130#endif // _LIBCPP_STD_VER >= 20
131
132_LIBCPP_POP_MACROS
133
134#endif // _LIBCPP___STOP_TOKEN_INTRUSIVE_SHARED_PTR_H
135