chromium/third_party/libc++/src/include/__atomic/atomic_sync.h

//===----------------------------------------------------------------------===//
//
// 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/cxx_atomic_impl.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 _Tp, class = void>
struct __atomic_waitable : false_type { … };

__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 &>()))>>;

template <class _AtomicWaitable, class _Poll>
struct __atomic_wait_poll_impl { … };

#ifndef _LIBCPP_HAS_NO_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 { … };

// 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, _Poll&& __poll, memory_order __order) { … }

template <class _AtomicWaitable>
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void __atomic_notify_one(const _AtomicWaitable& __a) { … }

template <class _AtomicWaitable>
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void __atomic_notify_all(const _AtomicWaitable& __a) { … }

#else // _LIBCPP_HAS_NO_THREADS

template <class _AtomicWaitable, class _Poll>
_LIBCPP_HIDE_FROM_ABI void __atomic_wait_unless(const _AtomicWaitable& __a, _Poll&& __poll, memory_order __order) {
  __atomic_wait_poll_impl<_AtomicWaitable, __decay_t<_Poll> > __poll_fn = {__a, __poll, __order};
  std::__libcpp_thread_poll_with_backoff(__poll_fn, __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_NO_THREADS

template <typename _Tp>
_LIBCPP_HIDE_FROM_ABI bool __cxx_nonatomic_compare_equal(_Tp const& __lhs, _Tp const& __rhs) { … }

template <class _Tp>
struct __atomic_compare_unequal_to { … };

template <class _AtomicWaitable, class _Up>
_LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void
__atomic_wait(_AtomicWaitable& __a, _Up __val, memory_order __order) { … }

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___ATOMIC_ATOMIC_SYNC_H