| //===----------------------------------------------------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef _LIBCPP___ATOMIC_ATOMIC_SYNC_H |
| #define _LIBCPP___ATOMIC_ATOMIC_SYNC_H |
| |
| #include <__atomic/contention_t.h> |
| #include <__atomic/memory_order.h> |
| #include <__atomic/to_gcc_order.h> |
| #include <__chrono/duration.h> |
| #include <__config> |
| #include <__memory/addressof.h> |
| #include <__thread/poll_with_backoff.h> |
| #include <__thread/support.h> |
| #include <__type_traits/conjunction.h> |
| #include <__type_traits/decay.h> |
| #include <__type_traits/invoke.h> |
| #include <__type_traits/void_t.h> |
| #include <__utility/declval.h> |
| #include <cstring> |
| |
| #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) |
| # pragma GCC system_header |
| #endif |
| |
| _LIBCPP_BEGIN_NAMESPACE_STD |
| |
| // The customisation points to enable the following functions: |
| // - __atomic_wait |
| // - __atomic_wait_unless |
| // - __atomic_notify_one |
| // - __atomic_notify_all |
| // Note that std::atomic<T>::wait was back-ported to C++03 |
| // The below implementations look ugly to support C++03 |
| template <class _Tp, class = void> |
| struct __atomic_waitable_traits { |
| template <class _AtomicWaitable> |
| static void __atomic_load(_AtomicWaitable&&, memory_order) = delete; |
| |
| template <class _AtomicWaitable> |
| static void __atomic_contention_address(_AtomicWaitable&&) = delete; |
| }; |
| |
| template <class _Tp, class = void> |
| struct __atomic_waitable : false_type {}; |
| |
| template <class _Tp> |
| struct __atomic_waitable< _Tp, |
| __void_t<decltype(__atomic_waitable_traits<__decay_t<_Tp> >::__atomic_load( |
| std::declval<const _Tp&>(), std::declval<memory_order>())), |
| decltype(__atomic_waitable_traits<__decay_t<_Tp> >::__atomic_contention_address( |
| std::declval<const _Tp&>()))> > : true_type {}; |
| |
| #if _LIBCPP_STD_VER >= 20 |
| # if _LIBCPP_HAS_THREADS |
| |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_one(void const volatile*) _NOEXCEPT; |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void __cxx_atomic_notify_all(void const volatile*) _NOEXCEPT; |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t |
| __libcpp_atomic_monitor(void const volatile*) _NOEXCEPT; |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void |
| __libcpp_atomic_wait(void const volatile*, __cxx_contention_t) _NOEXCEPT; |
| |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void |
| __cxx_atomic_notify_one(__cxx_atomic_contention_t const volatile*) _NOEXCEPT; |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void |
| __cxx_atomic_notify_all(__cxx_atomic_contention_t const volatile*) _NOEXCEPT; |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t |
| __libcpp_atomic_monitor(__cxx_atomic_contention_t const volatile*) _NOEXCEPT; |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_EXPORTED_FROM_ABI void |
| __libcpp_atomic_wait(__cxx_atomic_contention_t const volatile*, __cxx_contention_t) _NOEXCEPT; |
| |
| template <class _AtomicWaitable, class _Poll> |
| struct __atomic_wait_backoff_impl { |
| const _AtomicWaitable& __a_; |
| _Poll __poll_; |
| memory_order __order_; |
| |
| using __waitable_traits = __atomic_waitable_traits<__decay_t<_AtomicWaitable> >; |
| |
| _LIBCPP_AVAILABILITY_SYNC |
| _LIBCPP_HIDE_FROM_ABI bool |
| __update_monitor_val_and_poll(__cxx_atomic_contention_t const volatile*, __cxx_contention_t& __monitor_val) const { |
| // In case the contention type happens to be __cxx_atomic_contention_t, i.e. __cxx_atomic_impl<int64_t>, |
| // the platform wait is directly monitoring the atomic value itself. |
| // `__poll_` takes the current value of the atomic as an in-out argument |
| // to potentially modify it. After it returns, `__monitor` has a value |
| // which can be safely waited on by `std::__libcpp_atomic_wait` without any |
| // ABA style issues. |
| __monitor_val = __waitable_traits::__atomic_load(__a_, __order_); |
| return __poll_(__monitor_val); |
| } |
| |
| _LIBCPP_AVAILABILITY_SYNC |
| _LIBCPP_HIDE_FROM_ABI bool |
| __update_monitor_val_and_poll(void const volatile* __contention_address, __cxx_contention_t& __monitor_val) const { |
| // In case the contention type is anything else, platform wait is monitoring a __cxx_atomic_contention_t |
| // from the global pool, the monitor comes from __libcpp_atomic_monitor |
| __monitor_val = std::__libcpp_atomic_monitor(__contention_address); |
| auto __current_val = __waitable_traits::__atomic_load(__a_, __order_); |
| return __poll_(__current_val); |
| } |
| |
| _LIBCPP_AVAILABILITY_SYNC |
| _LIBCPP_HIDE_FROM_ABI bool operator()(chrono::nanoseconds __elapsed) const { |
| if (__elapsed > chrono::microseconds(64)) { |
| auto __contention_address = __waitable_traits::__atomic_contention_address(__a_); |
| __cxx_contention_t __monitor_val; |
| if (__update_monitor_val_and_poll(__contention_address, __monitor_val)) |
| return true; |
| std::__libcpp_atomic_wait(__contention_address, __monitor_val); |
| } else if (__elapsed > chrono::microseconds(4)) |
| __libcpp_thread_yield(); |
| else { |
| } // poll |
| return false; |
| } |
| }; |
| |
| // The semantics of this function are similar to `atomic`'s |
| // `.wait(T old, std::memory_order order)`, but instead of having a hardcoded |
| // predicate (is the loaded value unequal to `old`?), the predicate function is |
| // specified as an argument. The loaded value is given as an in-out argument to |
| // the predicate. If the predicate function returns `true`, |
| // `__atomic_wait_unless` will return. If the predicate function returns |
| // `false`, it must set the argument to its current understanding of the atomic |
| // value. The predicate function must not return `false` spuriously. |
| template <class _AtomicWaitable, class _Poll> |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void |
| __atomic_wait_unless(const _AtomicWaitable& __a, memory_order __order, _Poll&& __poll) { |
| static_assert(__atomic_waitable<_AtomicWaitable>::value, ""); |
| __atomic_wait_backoff_impl<_AtomicWaitable, __decay_t<_Poll> > __backoff_fn = {__a, __poll, __order}; |
| std::__libcpp_thread_poll_with_backoff( |
| /* poll */ |
| [&]() { |
| auto __current_val = __atomic_waitable_traits<__decay_t<_AtomicWaitable> >::__atomic_load(__a, __order); |
| return __poll(__current_val); |
| }, |
| /* backoff */ __backoff_fn); |
| } |
| |
| template <class _AtomicWaitable> |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void __atomic_notify_one(const _AtomicWaitable& __a) { |
| static_assert(__atomic_waitable<_AtomicWaitable>::value, ""); |
| std::__cxx_atomic_notify_one(__atomic_waitable_traits<__decay_t<_AtomicWaitable> >::__atomic_contention_address(__a)); |
| } |
| |
| template <class _AtomicWaitable> |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void __atomic_notify_all(const _AtomicWaitable& __a) { |
| static_assert(__atomic_waitable<_AtomicWaitable>::value, ""); |
| std::__cxx_atomic_notify_all(__atomic_waitable_traits<__decay_t<_AtomicWaitable> >::__atomic_contention_address(__a)); |
| } |
| |
| # else // _LIBCPP_HAS_THREADS |
| |
| template <class _AtomicWaitable, class _Poll> |
| _LIBCPP_HIDE_FROM_ABI void __atomic_wait_unless(const _AtomicWaitable& __a, memory_order __order, _Poll&& __poll) { |
| std::__libcpp_thread_poll_with_backoff( |
| /* poll */ |
| [&]() { |
| auto __current_val = __atomic_waitable_traits<__decay_t<_AtomicWaitable> >::__atomic_load(__a, __order); |
| return __poll(__current_val); |
| }, |
| /* backoff */ __spinning_backoff_policy()); |
| } |
| |
| template <class _AtomicWaitable> |
| _LIBCPP_HIDE_FROM_ABI void __atomic_notify_one(const _AtomicWaitable&) {} |
| |
| template <class _AtomicWaitable> |
| _LIBCPP_HIDE_FROM_ABI void __atomic_notify_all(const _AtomicWaitable&) {} |
| |
| # endif // _LIBCPP_HAS_THREADS |
| |
| template <typename _Tp> |
| _LIBCPP_HIDE_FROM_ABI bool __cxx_nonatomic_compare_equal(_Tp const& __lhs, _Tp const& __rhs) { |
| return std::memcmp(std::addressof(__lhs), std::addressof(__rhs), sizeof(_Tp)) == 0; |
| } |
| |
| template <class _AtomicWaitable, class _Tp> |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void |
| __atomic_wait(_AtomicWaitable& __a, _Tp __val, memory_order __order) { |
| static_assert(__atomic_waitable<_AtomicWaitable>::value, ""); |
| std::__atomic_wait_unless(__a, __order, [&](_Tp const& __current) { |
| return !std::__cxx_nonatomic_compare_equal(__current, __val); |
| }); |
| } |
| |
| #endif // C++20 |
| |
| _LIBCPP_END_NAMESPACE_STD |
| |
| #endif // _LIBCPP___ATOMIC_ATOMIC_SYNC_H |