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1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP___CXX03___ATOMIC_ATOMIC_SYNC_H
10#define _LIBCPP___CXX03___ATOMIC_ATOMIC_SYNC_H
11
12#include <__cxx03/__atomic/contention_t.h>
13#include <__cxx03/__atomic/cxx_atomic_impl.h>
14#include <__cxx03/__atomic/memory_order.h>
15#include <__cxx03/__atomic/to_gcc_order.h>
16#include <__cxx03/__chrono/duration.h>
17#include <__cxx03/__config>
18#include <__cxx03/__memory/addressof.h>
19#include <__cxx03/__thread/poll_with_backoff.h>
20#include <__cxx03/__thread/support.h>
21#include <__cxx03/__type_traits/conjunction.h>
22#include <__cxx03/__type_traits/decay.h>
23#include <__cxx03/__type_traits/invoke.h>
24#include <__cxx03/__type_traits/void_t.h>
25#include <__cxx03/__utility/declval.h>
26#include <__cxx03/cstring>
27
28#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
29# pragma GCC system_header
30#endif
31
32_LIBCPP_BEGIN_NAMESPACE_STD
33
34// The customisation points to enable the following functions:
35// - __atomic_wait
36// - __atomic_wait_unless
37// - __atomic_notify_one
38// - __atomic_notify_all
39// Note that std::atomic<T>::wait was back-ported to C++03
40// The below implementations look ugly to support C++03
41template <class _Tp, class = void>
42struct __atomic_waitable_traits {
43 template <class _AtomicWaitable>
44 static void __atomic_load(_AtomicWaitable&&, memory_order) = delete;
45
46 template <class _AtomicWaitable>
47 static void __atomic_contention_address(_AtomicWaitable&&) = delete;
48};
49
50template <class _Tp, class = void>
51struct __atomic_waitable : false_type {};
52
53template <class _Tp>
54struct __atomic_waitable< _Tp,
55 __void_t<decltype(__atomic_waitable_traits<__decay_t<_Tp> >::__atomic_load(
56 std::declval<const _Tp&>(), std::declval<memory_order>())),
57 decltype(__atomic_waitable_traits<__decay_t<_Tp> >::__atomic_contention_address(
58 std::declval<const _Tp&>()))> > : true_type {};
59
60template <class _AtomicWaitable, class _Poll>
61struct __atomic_wait_poll_impl {
62 const _AtomicWaitable& __a_;
63 _Poll __poll_;
64 memory_order __order_;
65
66 _LIBCPP_HIDE_FROM_ABI bool operator()() const {
67 auto __current_val = __atomic_waitable_traits<__decay_t<_AtomicWaitable> >::__atomic_load(__a_, __order_);
68 return __poll_(__current_val);
69 }
70};
71
72#ifndef _LIBCPP_HAS_NO_THREADS
73
74_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_one(void const volatile*) _NOEXCEPT;
75_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_all(void const volatile*) _NOEXCEPT;
76_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t
77__libcpp_atomic_monitor(void const volatile*) _NOEXCEPT;
78_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void
79__libcpp_atomic_wait(void const volatile*, __cxx_contention_t) _NOEXCEPT;
80
81_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void
82__cxx_atomic_notify_one(__cxx_atomic_contention_t const volatile*) _NOEXCEPT;
83_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void
84__cxx_atomic_notify_all(__cxx_atomic_contention_t const volatile*) _NOEXCEPT;
85_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t
86__libcpp_atomic_monitor(__cxx_atomic_contention_t const volatile*) _NOEXCEPT;
87_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void
88__libcpp_atomic_wait(__cxx_atomic_contention_t const volatile*, __cxx_contention_t) _NOEXCEPT;
89
90template <class _AtomicWaitable, class _Poll>
91struct __atomic_wait_backoff_impl {
92 const _AtomicWaitable& __a_;
93 _Poll __poll_;
94 memory_order __order_;
95
96 using __waitable_traits = __atomic_waitable_traits<__decay_t<_AtomicWaitable> >;
97
98 _LIBCPP_AVAILABILITY_SYNC
99 _LIBCPP_HIDE_FROM_ABI bool
100 __update_monitor_val_and_poll(__cxx_atomic_contention_t const volatile*, __cxx_contention_t& __monitor_val) const {
101 // In case the contention type happens to be __cxx_atomic_contention_t, i.e. __cxx_atomic_impl<int64_t>,
102 // the platform wait is directly monitoring the atomic value itself.
103 // `__poll_` takes the current value of the atomic as an in-out argument
104 // to potentially modify it. After it returns, `__monitor` has a value
105 // which can be safely waited on by `std::__libcpp_atomic_wait` without any
106 // ABA style issues.
107 __monitor_val = __waitable_traits::__atomic_load(__a_, __order_);
108 return __poll_(__monitor_val);
109 }
110
111 _LIBCPP_AVAILABILITY_SYNC
112 _LIBCPP_HIDE_FROM_ABI bool
113 __update_monitor_val_and_poll(void const volatile* __contention_address, __cxx_contention_t& __monitor_val) const {
114 // In case the contention type is anything else, platform wait is monitoring a __cxx_atomic_contention_t
115 // from the global pool, the monitor comes from __libcpp_atomic_monitor
116 __monitor_val = std::__libcpp_atomic_monitor(__contention_address);
117 auto __current_val = __waitable_traits::__atomic_load(__a_, __order_);
118 return __poll_(__current_val);
119 }
120
121 _LIBCPP_AVAILABILITY_SYNC
122 _LIBCPP_HIDE_FROM_ABI bool operator()(chrono::nanoseconds __elapsed) const {
123 if (__elapsed > chrono::microseconds(64)) {
124 auto __contention_address = __waitable_traits::__atomic_contention_address(__a_);
125 __cxx_contention_t __monitor_val;
126 if (__update_monitor_val_and_poll(__contention_address, __monitor_val))
127 return true;
128 std::__libcpp_atomic_wait(__contention_address, __monitor_val);
129 } else if (__elapsed > chrono::microseconds(4))
130 __libcpp_thread_yield();
131 else {
132 } // poll
133 return false;
134 }
135};
136
137// The semantics of this function are similar to `atomic`'s
138// `.wait(T old, std::memory_order order)`, but instead of having a hardcoded
139// predicate (is the loaded value unequal to `old`?), the predicate function is
140// specified as an argument. The loaded value is given as an in-out argument to
141// the predicate. If the predicate function returns `true`,
142// `__atomic_wait_unless` will return. If the predicate function returns
143// `false`, it must set the argument to its current understanding of the atomic
144// value. The predicate function must not return `false` spuriously.
145template <class _AtomicWaitable, class _Poll>
146_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
147__atomic_wait_unless(const _AtomicWaitable& __a, _Poll&& __poll, memory_order __order) {
148 static_assert(__atomic_waitable<_AtomicWaitable>::value, "");
149 __atomic_wait_poll_impl<_AtomicWaitable, __decay_t<_Poll> > __poll_impl = {__a, __poll, __order};
150 __atomic_wait_backoff_impl<_AtomicWaitable, __decay_t<_Poll> > __backoff_fn = {__a, __poll, __order};
151 std::__libcpp_thread_poll_with_backoff(__poll_impl, __backoff_fn);
152}
153
154template <class _AtomicWaitable>
155_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void __atomic_notify_one(const _AtomicWaitable& __a) {
156 static_assert(__atomic_waitable<_AtomicWaitable>::value, "");
157 std::__cxx_atomic_notify_one(__atomic_waitable_traits<__decay_t<_AtomicWaitable> >::__atomic_contention_address(__a));
158}
159
160template <class _AtomicWaitable>
161_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void __atomic_notify_all(const _AtomicWaitable& __a) {
162 static_assert(__atomic_waitable<_AtomicWaitable>::value, "");
163 std::__cxx_atomic_notify_all(__atomic_waitable_traits<__decay_t<_AtomicWaitable> >::__atomic_contention_address(__a));
164}
165
166#else // _LIBCPP_HAS_NO_THREADS
167
168template <class _AtomicWaitable, class _Poll>
169_LIBCPP_HIDE_FROM_ABI void __atomic_wait_unless(const _AtomicWaitable& __a, _Poll&& __poll, memory_order __order) {
170 __atomic_wait_poll_impl<_AtomicWaitable, __decay_t<_Poll> > __poll_fn = {__a, __poll, __order};
171 std::__libcpp_thread_poll_with_backoff(__poll_fn, __spinning_backoff_policy());
172}
173
174template <class _AtomicWaitable>
175_LIBCPP_HIDE_FROM_ABI void __atomic_notify_one(const _AtomicWaitable&) {}
176
177template <class _AtomicWaitable>
178_LIBCPP_HIDE_FROM_ABI void __atomic_notify_all(const _AtomicWaitable&) {}
179
180#endif // _LIBCPP_HAS_NO_THREADS
181
182template <typename _Tp>
183_LIBCPP_HIDE_FROM_ABI bool __cxx_nonatomic_compare_equal(_Tp const& __lhs, _Tp const& __rhs) {
184 return std::memcmp(std::addressof(__lhs), std::addressof(__rhs), sizeof(_Tp)) == 0;
185}
186
187template <class _Tp>
188struct __atomic_compare_unequal_to {
189 _Tp __val_;
190 _LIBCPP_HIDE_FROM_ABI bool operator()(const _Tp& __arg) const {
191 return !std::__cxx_nonatomic_compare_equal(__arg, __val_);
192 }
193};
194
195template <class _AtomicWaitable, class _Up>
196_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
197__atomic_wait(_AtomicWaitable& __a, _Up __val, memory_order __order) {
198 static_assert(__atomic_waitable<_AtomicWaitable>::value, "");
199 __atomic_compare_unequal_to<_Up> __nonatomic_equal = {__val};
200 std::__atomic_wait_unless(__a, __nonatomic_equal, __order);
201}
202
203_LIBCPP_END_NAMESPACE_STD
204
205#endif // _LIBCPP___CXX03___ATOMIC_ATOMIC_SYNC_H
206

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source code of libcxx/include/__cxx03/__atomic/atomic_sync.h