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/atomic.h> 14 #include <__atomic/memory_order.h> 15 #include <__config> 16 #include <__type_traits/is_reference.h> 17 #include <__utility/move.h> 18 #include <__utility/swap.h> 19 #include <cstddef> 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 _LIBCPP_BEGIN_NAMESPACE_STD 29 30 #if _LIBCPP_STD_VER >= 20 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. 38 template <class _Tp> 39 struct __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 44 template <class _Tp> 45 struct __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(*__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(*__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(*__other.__raw_ptr_); 68 } 69 if (__raw_ptr_) { 70 __decrement_ref_count(*__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(*this); 79 return *this; 80 } 81 82 _LIBCPP_HIDE_FROM_ABI ~__intrusive_shared_ptr() { 83 if (__raw_ptr_) { 84 __decrement_ref_count(*__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(__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 } 104 105 private: 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 &__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 #endif // _LIBCPP_STD_VER >= 20 129 130 _LIBCPP_END_NAMESPACE_STD 131 132 _LIBCPP_POP_MACROS 133 134 #endif // _LIBCPP___STOP_TOKEN_INTRUSIVE_SHARED_PTR_H 135