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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-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef _LIBCPP___CXX03___ATOMIC_ATOMIC_SYNC_H10#define _LIBCPP___CXX03___ATOMIC_ATOMIC_SYNC_H11 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_header30#endif31 32_LIBCPP_BEGIN_NAMESPACE_STD33 34// The customisation points to enable the following functions:35// - __atomic_wait36// - __atomic_wait_unless37// - __atomic_notify_one38// - __atomic_notify_all39// Note that std::atomic<T>::wait was back-ported to C++0340// The below implementations look ugly to support C++0341template <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_THREADS73 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_t77__libcpp_atomic_monitor(void const volatile*) _NOEXCEPT;78_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void79__libcpp_atomic_wait(void const volatile*, __cxx_contention_t) _NOEXCEPT;80 81_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void82__cxx_atomic_notify_one(__cxx_atomic_contention_t const volatile*) _NOEXCEPT;83_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void84__cxx_atomic_notify_all(__cxx_atomic_contention_t const volatile*) _NOEXCEPT;85_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t86__libcpp_atomic_monitor(__cxx_atomic_contention_t const volatile*) _NOEXCEPT;87_LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void88__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_SYNC99 _LIBCPP_HIDE_FROM_ABI bool100 __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 argument104 // to potentially modify it. After it returns, `__monitor` has a value105 // which can be safely waited on by `std::__libcpp_atomic_wait` without any106 // ABA style issues.107 __monitor_val = __waitable_traits::__atomic_load(__a_, __order_);108 return __poll_(__monitor_val);109 }110 111 _LIBCPP_AVAILABILITY_SYNC112 _LIBCPP_HIDE_FROM_ABI bool113 __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_t115 // from the global pool, the monitor comes from __libcpp_atomic_monitor116 __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_SYNC122 _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 } // poll133 return false;134 }135};136 137// The semantics of this function are similar to `atomic`'s138// `.wait(T old, std::memory_order order)`, but instead of having a hardcoded139// predicate (is the loaded value unequal to `old`?), the predicate function is140// specified as an argument. The loaded value is given as an in-out argument to141// the predicate. If the predicate function returns `true`,142// `__atomic_wait_unless` will return. If the predicate function returns143// `false`, it must set the argument to its current understanding of the atomic144// value. The predicate function must not return `false` spuriously.145template <class _AtomicWaitable, class _Poll>146_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void147__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_THREADS167 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_THREADS181 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 void197__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_STD204 205#endif // _LIBCPP___CXX03___ATOMIC_ATOMIC_SYNC_H206