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___ATOMIC_ATOMIC_SYNC_H 10 #define _LIBCPP___ATOMIC_ATOMIC_SYNC_H 11 12 #include <__atomic/contention_t.h> 13 #include <__atomic/cxx_atomic_impl.h> 14 #include <__atomic/memory_order.h> 15 #include <__atomic/to_gcc_order.h> 16 #include <__chrono/duration.h> 17 #include <__config> 18 #include <__memory/addressof.h> 19 #include <__thread/poll_with_backoff.h> 20 #include <__thread/support.h> 21 #include <__type_traits/conjunction.h> 22 #include <__type_traits/decay.h> 23 #include <__type_traits/invoke.h> 24 #include <__type_traits/void_t.h> 25 #include <__utility/declval.h> 26 #include <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 41 template <class _Tp, class = void> 42 struct __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 50 template <class _Tp, class = void> 51 struct __atomic_waitable : false_type {}; 52 53 template <class _Tp> 54 struct __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 60 template <class _AtomicWaitable, class _Poll> 61 struct __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 90 template <class _AtomicWaitable, class _Poll> 91 struct __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. 145 template <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 } 153 154 template <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 } 159 160 template <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 167 168 template <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 } 173 174 template <class _AtomicWaitable> 175 _LIBCPP_HIDE_FROM_ABI void __atomic_notify_one(const _AtomicWaitable&) {} 176 177 template <class _AtomicWaitable> 178 _LIBCPP_HIDE_FROM_ABI void __atomic_notify_all(const _AtomicWaitable&) {} 179 180 #endif // _LIBCPP_HAS_NO_THREADS 181 182 template <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 } 186 187 template <class _Tp> 188 struct __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 }; 194 195 template <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___ATOMIC_ATOMIC_SYNC_H 206