libstdc++-v3/include/bits/atomic_timed_wait.h - gcc - Git at Google

 // -*- C++ -*- header.

 // Copyright (C) 2020-2022 Free Software Foundation, Inc.
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
 // software; you can redistribute it and/or modify it under the
 // terms of the GNU General Public License as published by the
 // Free Software Foundation; either version 3, or (at your option)
 // any later version.

 // This library is distributed in the hope that it will be useful,
 // but WITHOUT ANY WARRANTY; without even the implied warranty of
 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 // GNU General Public License for more details.

 // Under Section 7 of GPL version 3, you are granted additional
 // permissions described in the GCC Runtime Library Exception, version
 // 3.1, as published by the Free Software Foundation.

 // You should have received a copy of the GNU General Public License and
 // a copy of the GCC Runtime Library Exception along with this program;
 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 // <http://www.gnu.org/licenses/>.

 /** @file bits/atomic_timed_wait.h
  *  This is an internal header file, included by other library headers.
  *  Do not attempt to use it directly. @headername{atomic}
  */

 #ifndef _GLIBCXX_ATOMIC_TIMED_WAIT_H
 #define _GLIBCXX_ATOMIC_TIMED_WAIT_H 1

 #pragma GCC system_header

 #include <bits/atomic_wait.h>

 #if __cpp_lib_atomic_wait
 #include <bits/functional_hash.h>
 #include <bits/this_thread_sleep.h>
 #include <bits/chrono.h>

 #ifdef _GLIBCXX_HAVE_LINUX_FUTEX
 #include <sys/time.h>
 #endif

 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION

   namespace __detail
   {
     using __wait_clock_t = chrono::steady_clock;

     template<typename _Clock, typename _Dur>
       __wait_clock_t::time_point
       __to_wait_clock(const chrono::time_point<_Clock, _Dur>& __atime) noexcept
       {
 	const typename _Clock::time_point __c_entry = _Clock::now();
 	const __wait_clock_t::time_point __w_entry = __wait_clock_t::now();
 	const auto __delta = __atime - __c_entry;
 	using __w_dur = typename __wait_clock_t::duration;
 	return __w_entry + chrono::ceil<__w_dur>(__delta);
       }

     template<typename _Dur>
       __wait_clock_t::time_point
       __to_wait_clock(const chrono::time_point<__wait_clock_t,
 					       _Dur>& __atime) noexcept
       {
 	using __w_dur = typename __wait_clock_t::duration;
 	return chrono::ceil<__w_dur>(__atime);
       }

 #ifdef _GLIBCXX_HAVE_LINUX_FUTEX
 #define _GLIBCXX_HAVE_PLATFORM_TIMED_WAIT
     // returns true if wait ended before timeout
     template<typename _Dur>
       bool
       __platform_wait_until_impl(const __platform_wait_t* __addr,
 				 __platform_wait_t __old,
 				 const chrono::time_point<__wait_clock_t, _Dur>&
 				      __atime) noexcept
       {
 	auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
 	auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);

 	struct timespec __rt =
 	{
 	  static_cast<std::time_t>(__s.time_since_epoch().count()),
 	  static_cast<long>(__ns.count())
 	};

 	auto __e = syscall (SYS_futex, __addr,
 			    static_cast<int>(__futex_wait_flags::
 						__wait_bitset_private),
 			    __old, &__rt, nullptr,
 			    static_cast<int>(__futex_wait_flags::
 						__bitset_match_any));

 	if (__e)
 	  {
 	    if (errno == ETIMEDOUT)
 	      return false;
 	    if (errno != EINTR && errno != EAGAIN)
 	      __throw_system_error(errno);
 	  }
 	return true;
       }

     // returns true if wait ended before timeout
     template<typename _Clock, typename _Dur>
       bool
       __platform_wait_until(const __platform_wait_t* __addr, __platform_wait_t __old,
 			    const chrono::time_point<_Clock, _Dur>& __atime)
       {
 	if constexpr (is_same_v<__wait_clock_t, _Clock>)
 	  {
 	    return __platform_wait_until_impl(__addr, __old, __atime);
 	  }
 	else
 	  {
 	    if (!__platform_wait_until_impl(__addr, __old,
 					    __to_wait_clock(__atime)))
 	      {
 		// We got a timeout when measured against __clock_t but
 		// we need to check against the caller-supplied clock
 		// to tell whether we should return a timeout.
 		if (_Clock::now() < __atime)
 		  return true;
 	      }
 	    return false;
 	  }
       }
 #else
 // define _GLIBCXX_HAVE_PLATFORM_TIMED_WAIT and implement __platform_wait_until()
 // if there is a more efficient primitive supported by the platform
 // (e.g. __ulock_wait())which is better than pthread_cond_clockwait
 #endif // ! PLATFORM_TIMED_WAIT

 #ifdef _GLIBCXX_HAS_GTHREADS
     // Returns true if wait ended before timeout.
     // _Clock must be either steady_clock or system_clock.
     template<typename _Clock, typename _Dur>
       bool
       __cond_wait_until_impl(__condvar& __cv, mutex& __mx,
 			     const chrono::time_point<_Clock, _Dur>& __atime)
       {
 	static_assert(std::__is_one_of<_Clock, chrono::steady_clock,
 					       chrono::system_clock>::value);

 	auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
 	auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);

 	__gthread_time_t __ts =
 	  {
 	    static_cast<std::time_t>(__s.time_since_epoch().count()),
 	    static_cast<long>(__ns.count())
 	  };

 #ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
 	if constexpr (is_same_v<chrono::steady_clock, _Clock>)
 	  __cv.wait_until(__mx, CLOCK_MONOTONIC, __ts);
 	else
 #endif
 	  __cv.wait_until(__mx, __ts);
 	return _Clock::now() < __atime;
       }

     // returns true if wait ended before timeout
     template<typename _Clock, typename _Dur>
       bool
       __cond_wait_until(__condvar& __cv, mutex& __mx,
 	  const chrono::time_point<_Clock, _Dur>& __atime)
       {
 #ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
 	if constexpr (is_same_v<_Clock, chrono::steady_clock>)
 	  return __detail::__cond_wait_until_impl(__cv, __mx, __atime);
 	else
 #endif
 	if constexpr (is_same_v<_Clock, chrono::system_clock>)
 	  return __detail::__cond_wait_until_impl(__cv, __mx, __atime);
 	else
 	  {
 	    if (__cond_wait_until_impl(__cv, __mx,
 				       __to_wait_clock(__atime)))
 	      {
 		// We got a timeout when measured against __clock_t but
 		// we need to check against the caller-supplied clock
 		// to tell whether we should return a timeout.
 		if (_Clock::now() < __atime)
 		  return true;
 	      }
 	    return false;
 	  }
       }
 #endif // _GLIBCXX_HAS_GTHREADS

     struct __timed_waiter_pool : __waiter_pool_base
     {
       // returns true if wait ended before timeout
       template<typename _Clock, typename _Dur>
 	bool
 	_M_do_wait_until(__platform_wait_t* __addr, __platform_wait_t __old,
 			 const chrono::time_point<_Clock, _Dur>& __atime)
 	{
 #ifdef _GLIBCXX_HAVE_PLATFORM_TIMED_WAIT
 	  return __platform_wait_until(__addr, __old, __atime);
 #else
 	  __platform_wait_t __val;
 	  __atomic_load(__addr, &__val, __ATOMIC_RELAXED);
 	  if (__val == __old)
 	    {
 	      lock_guard<mutex> __l(_M_mtx);
 	      return __cond_wait_until(_M_cv, _M_mtx, __atime);
 	    }
 	  else
 	    return true;
 #endif // _GLIBCXX_HAVE_PLATFORM_TIMED_WAIT
 	}
     };

     struct __timed_backoff_spin_policy
     {
       __wait_clock_t::time_point _M_deadline;
       __wait_clock_t::time_point _M_t0;

       template<typename _Clock, typename _Dur>
 	__timed_backoff_spin_policy(chrono::time_point<_Clock, _Dur>
 				      __deadline = _Clock::time_point::max(),
 				    chrono::time_point<_Clock, _Dur>
 				      __t0 = _Clock::now()) noexcept
 	  : _M_deadline(__to_wait_clock(__deadline))
 	  , _M_t0(__to_wait_clock(__t0))
 	{ }

       bool
       operator()() const noexcept
       {
 	using namespace literals::chrono_literals;
 	auto __now = __wait_clock_t::now();
 	if (_M_deadline <= __now)
 	  return false;

 	// FIXME: this_thread::sleep_for not available #ifdef _GLIBCXX_NO_SLEEP

 	auto __elapsed = __now - _M_t0;
 	if (__elapsed > 128ms)
 	  {
 	    this_thread::sleep_for(64ms);
 	  }
 	else if (__elapsed > 64us)
 	  {
 	    this_thread::sleep_for(__elapsed / 2);
 	  }
 	else if (__elapsed > 4us)
 	  {
 	    __thread_yield();
 	  }
 	else
 	  return false;
 	return true;
       }
     };

     template<typename _EntersWait>
       struct __timed_waiter : __waiter_base<__timed_waiter_pool>
       {
 	using __base_type = __waiter_base<__timed_waiter_pool>;

 	template<typename _Tp>
 	  __timed_waiter(const _Tp* __addr) noexcept
 	  : __base_type(__addr)
 	{
 	  if constexpr (_EntersWait::value)
 	    _M_w._M_enter_wait();
 	}

 	~__timed_waiter()
 	{
 	  if constexpr (_EntersWait::value)
 	    _M_w._M_leave_wait();
 	}

 	// returns true if wait ended before timeout
 	template<typename _Tp, typename _ValFn,
 		 typename _Clock, typename _Dur>
 	  bool
 	  _M_do_wait_until_v(_Tp __old, _ValFn __vfn,
 			     const chrono::time_point<_Clock, _Dur>&
 								__atime) noexcept
 	  {
 	    __platform_wait_t __val;
 	    if (_M_do_spin(__old, std::move(__vfn), __val,
 			   __timed_backoff_spin_policy(__atime)))
 	      return true;
 	    return __base_type::_M_w._M_do_wait_until(__base_type::_M_addr, __val, __atime);
 	  }

 	// returns true if wait ended before timeout
 	template<typename _Pred,
 		 typename _Clock, typename _Dur>
 	  bool
 	  _M_do_wait_until(_Pred __pred, __platform_wait_t __val,
 			  const chrono::time_point<_Clock, _Dur>&
 							      __atime) noexcept
 	  {
 	    for (auto __now = _Clock::now(); __now < __atime;
 		  __now = _Clock::now())
 	      {
 		if (__base_type::_M_w._M_do_wait_until(
 		      __base_type::_M_addr, __val, __atime)
 		    && __pred())
 		  return true;

 		if (__base_type::_M_do_spin(__pred, __val,
 			       __timed_backoff_spin_policy(__atime, __now)))
 		  return true;
 	      }
 	    return false;
 	  }

 	// returns true if wait ended before timeout
 	template<typename _Pred,
 		 typename _Clock, typename _Dur>
 	  bool
 	  _M_do_wait_until(_Pred __pred,
 			   const chrono::time_point<_Clock, _Dur>&
 								__atime) noexcept
 	  {
 	    __platform_wait_t __val;
 	    if (__base_type::_M_do_spin(__pred, __val,
 					__timed_backoff_spin_policy(__atime)))
 	      return true;
 	    return _M_do_wait_until(__pred, __val, __atime);
 	  }

 	template<typename _Tp, typename _ValFn,
 		 typename _Rep, typename _Period>
 	  bool
 	  _M_do_wait_for_v(_Tp __old, _ValFn __vfn,
 			   const chrono::duration<_Rep, _Period>&
 								__rtime) noexcept
 	  {
 	    __platform_wait_t __val;
 	    if (_M_do_spin_v(__old, std::move(__vfn), __val))
 	      return true;

 	    if (!__rtime.count())
 	      return false; // no rtime supplied, and spin did not acquire

 	    auto __reltime = chrono::ceil<__wait_clock_t::duration>(__rtime);

 	    return __base_type::_M_w._M_do_wait_until(
 					  __base_type::_M_addr,
 					  __val,
 					  chrono::steady_clock::now() + __reltime);
 	  }

 	template<typename _Pred,
 		 typename _Rep, typename _Period>
 	  bool
 	  _M_do_wait_for(_Pred __pred,
 			 const chrono::duration<_Rep, _Period>& __rtime) noexcept
 	  {
 	    __platform_wait_t __val;
 	    if (__base_type::_M_do_spin(__pred, __val))
 	      return true;

 	    if (!__rtime.count())
 	      return false; // no rtime supplied, and spin did not acquire

 	    auto __reltime = chrono::ceil<__wait_clock_t::duration>(__rtime);

 	    return _M_do_wait_until(__pred, __val,
 				    chrono::steady_clock::now() + __reltime);
 	  }
       };

     using __enters_timed_wait = __timed_waiter<std::true_type>;
     using __bare_timed_wait = __timed_waiter<std::false_type>;
   } // namespace __detail

   // returns true if wait ended before timeout
   template<typename _Tp, typename _ValFn,
 	   typename _Clock, typename _Dur>
     bool
     __atomic_wait_address_until_v(const _Tp* __addr, _Tp&& __old, _ValFn&& __vfn,
 			const chrono::time_point<_Clock, _Dur>&
 			    __atime) noexcept
     {
       __detail::__enters_timed_wait __w{__addr};
       return __w._M_do_wait_until_v(__old, __vfn, __atime);
     }

   template<typename _Tp, typename _Pred,
 	   typename _Clock, typename _Dur>
     bool
     __atomic_wait_address_until(const _Tp* __addr, _Pred __pred,
 				const chrono::time_point<_Clock, _Dur>&
 							      __atime) noexcept
     {
       __detail::__enters_timed_wait __w{__addr};
       return __w._M_do_wait_until(__pred, __atime);
     }

   template<typename _Pred,
 	   typename _Clock, typename _Dur>
     bool
     __atomic_wait_address_until_bare(const __detail::__platform_wait_t* __addr,
 				_Pred __pred,
 				const chrono::time_point<_Clock, _Dur>&
 							      __atime) noexcept
     {
       __detail::__bare_timed_wait __w{__addr};
       return __w._M_do_wait_until(__pred, __atime);
     }

   template<typename _Tp, typename _ValFn,
 	   typename _Rep, typename _Period>
     bool
     __atomic_wait_address_for_v(const _Tp* __addr, _Tp&& __old, _ValFn&& __vfn,
 		      const chrono::duration<_Rep, _Period>& __rtime) noexcept
     {
       __detail::__enters_timed_wait __w{__addr};
       return __w._M_do_wait_for_v(__old, __vfn, __rtime);
     }

   template<typename _Tp, typename _Pred,
 	   typename _Rep, typename _Period>
     bool
     __atomic_wait_address_for(const _Tp* __addr, _Pred __pred,
 		      const chrono::duration<_Rep, _Period>& __rtime) noexcept
     {

       __detail::__enters_timed_wait __w{__addr};
       return __w._M_do_wait_for(__pred, __rtime);
     }

   template<typename _Pred,
 	   typename _Rep, typename _Period>
     bool
     __atomic_wait_address_for_bare(const __detail::__platform_wait_t* __addr,
 			_Pred __pred,
 			const chrono::duration<_Rep, _Period>& __rtime) noexcept
     {
       __detail::__bare_timed_wait __w{__addr};
       return __w._M_do_wait_for(__pred, __rtime);
     }
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace std
 #endif // __cpp_lib_atomic_wait
 #endif // _GLIBCXX_ATOMIC_TIMED_WAIT_H
	// -- C++ -- header.

	// Copyright (C) 2020-2022 Free Software Foundation, Inc.
	//
	// This file is part of the GNU ISO C++ Library. This library is free
	// software; you can redistribute it and/or modify it under the
	// terms of the GNU General Public License as published by the
	// Free Software Foundation; either version 3, or (at your option)
	// any later version.

	// This library is distributed in the hope that it will be useful,
	// but WITHOUT ANY WARRANTY; without even the implied warranty of
	// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	// GNU General Public License for more details.

	// Under Section 7 of GPL version 3, you are granted additional
	// permissions described in the GCC Runtime Library Exception, version
	// 3.1, as published by the Free Software Foundation.

	// You should have received a copy of the GNU General Public License and
	// a copy of the GCC Runtime Library Exception along with this program;
	// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
	// <http://www.gnu.org/licenses/>.

	/** @file bits/atomic_timed_wait.h
	* This is an internal header file, included by other library headers.
	* Do not attempt to use it directly. @headername{atomic}
	*/

	#ifndef _GLIBCXX_ATOMIC_TIMED_WAIT_H
	#define _GLIBCXX_ATOMIC_TIMED_WAIT_H 1

	#pragma GCC system_header

	#include <bits/atomic_wait.h>

	#if __cpp_lib_atomic_wait
	#include <bits/functional_hash.h>
	#include <bits/this_thread_sleep.h>
	#include <bits/chrono.h>

	#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
	#include <sys/time.h>
	#endif

	namespace std _GLIBCXX_VISIBILITY(default)
	{
	_GLIBCXX_BEGIN_NAMESPACE_VERSION

	namespace __detail
	{
	using __wait_clock_t = chrono::steady_clock;

	template<typename _Clock, typename _Dur>
	__wait_clock_t::time_point
	__to_wait_clock(const chrono::time_point<_Clock, _Dur>& __atime) noexcept
	{
	const typename _Clock::time_point __c_entry = _Clock::now();
	const __wait_clock_t::time_point __w_entry = __wait_clock_t::now();
	const auto __delta = __atime - __c_entry;
	using __w_dur = typename __wait_clock_t::duration;
	return __w_entry + chrono::ceil<__w_dur>(__delta);
	}

	template<typename _Dur>
	__wait_clock_t::time_point
	__to_wait_clock(const chrono::time_point<__wait_clock_t,
	_Dur>& __atime) noexcept
	{
	using __w_dur = typename __wait_clock_t::duration;
	return chrono::ceil<__w_dur>(__atime);
	}

	#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
	#define _GLIBCXX_HAVE_PLATFORM_TIMED_WAIT
	// returns true if wait ended before timeout
	template<typename _Dur>
	bool
	__platform_wait_until_impl(const __platform_wait_t* __addr,
	__platform_wait_t __old,
	const chrono::time_point<__wait_clock_t, _Dur>&
	__atime) noexcept
	{
	auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
	auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);

	struct timespec __rt =
	{
	static_cast<std::time_t>(__s.time_since_epoch().count()),
	static_cast<long>(__ns.count())
	};

	auto __e = syscall (SYS_futex, __addr,
	static_cast<int>(__futex_wait_flags::
	__wait_bitset_private),
	__old, &__rt, nullptr,
	static_cast<int>(__futex_wait_flags::
	__bitset_match_any));

	if (__e)
	{
	if (errno == ETIMEDOUT)
	return false;
	if (errno != EINTR && errno != EAGAIN)
	__throw_system_error(errno);
	}
	return true;
	}

	// returns true if wait ended before timeout
	template<typename _Clock, typename _Dur>
	bool
	__platform_wait_until(const __platform_wait_t* __addr, __platform_wait_t __old,
	const chrono::time_point<_Clock, _Dur>& __atime)
	{
	if constexpr (is_same_v<__wait_clock_t, _Clock>)
	{
	return __platform_wait_until_impl(__addr, __old, __atime);
	}
	else
	{
	if (!__platform_wait_until_impl(__addr, __old,
	__to_wait_clock(__atime)))
	{
	// We got a timeout when measured against __clock_t but
	// we need to check against the caller-supplied clock
	// to tell whether we should return a timeout.
	if (_Clock::now() < __atime)
	return true;
	}
	return false;
	}
	}
	#else
	// define _GLIBCXX_HAVE_PLATFORM_TIMED_WAIT and implement __platform_wait_until()
	// if there is a more efficient primitive supported by the platform
	// (e.g. __ulock_wait())which is better than pthread_cond_clockwait
	#endif // ! PLATFORM_TIMED_WAIT

	#ifdef _GLIBCXX_HAS_GTHREADS
	// Returns true if wait ended before timeout.
	// _Clock must be either steady_clock or system_clock.
	template<typename _Clock, typename _Dur>
	bool
	__cond_wait_until_impl(__condvar& __cv, mutex& __mx,
	const chrono::time_point<_Clock, _Dur>& __atime)
	{
	static_assert(std::__is_one_of<_Clock, chrono::steady_clock,
	chrono::system_clock>::value);

	auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
	auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);

	__gthread_time_t __ts =
	{
	static_cast<std::time_t>(__s.time_since_epoch().count()),
	static_cast<long>(__ns.count())
	};

	#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
	if constexpr (is_same_v<chrono::steady_clock, _Clock>)
	__cv.wait_until(__mx, CLOCK_MONOTONIC, __ts);
	else
	#endif
	__cv.wait_until(__mx, __ts);
	return _Clock::now() < __atime;
	}

	// returns true if wait ended before timeout
	template<typename _Clock, typename _Dur>
	bool
	__cond_wait_until(__condvar& __cv, mutex& __mx,
	const chrono::time_point<_Clock, _Dur>& __atime)
	{
	#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
	if constexpr (is_same_v<_Clock, chrono::steady_clock>)
	return __detail::__cond_wait_until_impl(__cv, __mx, __atime);
	else
	#endif
	if constexpr (is_same_v<_Clock, chrono::system_clock>)
	return __detail::__cond_wait_until_impl(__cv, __mx, __atime);
	else
	{
	if (__cond_wait_until_impl(__cv, __mx,
	__to_wait_clock(__atime)))
	{
	// We got a timeout when measured against __clock_t but
	// we need to check against the caller-supplied clock
	// to tell whether we should return a timeout.
	if (_Clock::now() < __atime)
	return true;
	}
	return false;
	}
	}
	#endif // _GLIBCXX_HAS_GTHREADS

	struct __timed_waiter_pool : __waiter_pool_base
	{
	// returns true if wait ended before timeout
	template<typename _Clock, typename _Dur>
	bool
	_M_do_wait_until(__platform_wait_t* __addr, __platform_wait_t __old,
	const chrono::time_point<_Clock, _Dur>& __atime)
	{
	#ifdef _GLIBCXX_HAVE_PLATFORM_TIMED_WAIT
	return __platform_wait_until(__addr, __old, __atime);
	#else
	__platform_wait_t __val;
	__atomic_load(__addr, &__val, __ATOMIC_RELAXED);
	if (__val == __old)
	{
	lock_guard<mutex> __l(_M_mtx);
	return __cond_wait_until(_M_cv, _M_mtx, __atime);
	}
	else
	return true;
	#endif // _GLIBCXX_HAVE_PLATFORM_TIMED_WAIT
	}
	};

	struct __timed_backoff_spin_policy
	{
	__wait_clock_t::time_point _M_deadline;
	__wait_clock_t::time_point _M_t0;

	template<typename _Clock, typename _Dur>
	__timed_backoff_spin_policy(chrono::time_point<_Clock, _Dur>
	__deadline = _Clock::time_point::max(),
	chrono::time_point<_Clock, _Dur>
	__t0 = _Clock::now()) noexcept
	: _M_deadline(__to_wait_clock(__deadline))
	, _M_t0(__to_wait_clock(__t0))
	{ }

	bool
	operator()() const noexcept
	{
	using namespace literals::chrono_literals;
	auto __now = __wait_clock_t::now();
	if (_M_deadline <= __now)
	return false;

	// FIXME: this_thread::sleep_for not available #ifdef _GLIBCXX_NO_SLEEP

	auto __elapsed = __now - _M_t0;
	if (__elapsed > 128ms)
	{
	this_thread::sleep_for(64ms);
	}
	else if (__elapsed > 64us)
	{
	this_thread::sleep_for(__elapsed / 2);
	}
	else if (__elapsed > 4us)
	{
	__thread_yield();
	}
	else
	return false;
	return true;
	}
	};

	template<typename _EntersWait>
	struct __timed_waiter : __waiter_base<__timed_waiter_pool>
	{
	using __base_type = __waiter_base<__timed_waiter_pool>;

	template<typename _Tp>
	__timed_waiter(const _Tp* __addr) noexcept
	: __base_type(__addr)
	{
	if constexpr (_EntersWait::value)
	_M_w._M_enter_wait();
	}

	~__timed_waiter()
	{
	if constexpr (_EntersWait::value)
	_M_w._M_leave_wait();
	}

	// returns true if wait ended before timeout
	template<typename _Tp, typename _ValFn,
	typename _Clock, typename _Dur>
	bool
	_M_do_wait_until_v(_Tp __old, _ValFn __vfn,
	const chrono::time_point<_Clock, _Dur>&
	__atime) noexcept
	{
	__platform_wait_t __val;
	if (_M_do_spin(__old, std::move(__vfn), __val,
	__timed_backoff_spin_policy(__atime)))
	return true;
	return __base_type::_M_w._M_do_wait_until(__base_type::_M_addr, __val, __atime);
	}

	// returns true if wait ended before timeout
	template<typename _Pred,
	typename _Clock, typename _Dur>
	bool
	_M_do_wait_until(_Pred __pred, __platform_wait_t __val,
	const chrono::time_point<_Clock, _Dur>&
	__atime) noexcept
	{
	for (auto __now = _Clock::now(); __now < __atime;
	__now = _Clock::now())
	{
	if (__base_type::_M_w._M_do_wait_until(
	__base_type::_M_addr, __val, __atime)
	&& __pred())
	return true;

	if (__base_type::_M_do_spin(__pred, __val,
	__timed_backoff_spin_policy(__atime, __now)))
	return true;
	}
	return false;
	}

	// returns true if wait ended before timeout
	template<typename _Pred,
	typename _Clock, typename _Dur>
	bool
	_M_do_wait_until(_Pred __pred,
	const chrono::time_point<_Clock, _Dur>&
	__atime) noexcept
	{
	__platform_wait_t __val;
	if (__base_type::_M_do_spin(__pred, __val,
	__timed_backoff_spin_policy(__atime)))
	return true;
	return _M_do_wait_until(__pred, __val, __atime);
	}

	template<typename _Tp, typename _ValFn,
	typename _Rep, typename _Period>
	bool
	_M_do_wait_for_v(_Tp __old, _ValFn __vfn,
	const chrono::duration<_Rep, _Period>&
	__rtime) noexcept
	{
	__platform_wait_t __val;
	if (_M_do_spin_v(__old, std::move(__vfn), __val))
	return true;

	if (!__rtime.count())
	return false; // no rtime supplied, and spin did not acquire

	auto __reltime = chrono::ceil<__wait_clock_t::duration>(__rtime);

	return __base_type::_M_w._M_do_wait_until(
	__base_type::_M_addr,
	__val,
	chrono::steady_clock::now() + __reltime);
	}

	template<typename _Pred,
	typename _Rep, typename _Period>
	bool
	_M_do_wait_for(_Pred __pred,
	const chrono::duration<_Rep, _Period>& __rtime) noexcept
	{
	__platform_wait_t __val;
	if (__base_type::_M_do_spin(__pred, __val))
	return true;

	if (!__rtime.count())
	return false; // no rtime supplied, and spin did not acquire

	auto __reltime = chrono::ceil<__wait_clock_t::duration>(__rtime);

	return _M_do_wait_until(__pred, __val,
	chrono::steady_clock::now() + __reltime);
	}
	};

	using __enters_timed_wait = __timed_waiter<std::true_type>;
	using __bare_timed_wait = __timed_waiter<std::false_type>;
	} // namespace __detail

	// returns true if wait ended before timeout
	template<typename _Tp, typename _ValFn,
	typename _Clock, typename _Dur>
	bool
	__atomic_wait_address_until_v(const _Tp* __addr, _Tp&& __old, _ValFn&& __vfn,
	const chrono::time_point<_Clock, _Dur>&
	__atime) noexcept
	{
	__detail::__enters_timed_wait __w{__addr};
	return __w._M_do_wait_until_v(__old, __vfn, __atime);
	}

	template<typename _Tp, typename _Pred,
	typename _Clock, typename _Dur>
	bool
	__atomic_wait_address_until(const _Tp* __addr, _Pred __pred,
	const chrono::time_point<_Clock, _Dur>&
	__atime) noexcept
	{
	__detail::__enters_timed_wait __w{__addr};
	return __w._M_do_wait_until(__pred, __atime);
	}

	template<typename _Pred,
	typename _Clock, typename _Dur>
	bool
	__atomic_wait_address_until_bare(const __detail::__platform_wait_t* __addr,
	_Pred __pred,
	const chrono::time_point<_Clock, _Dur>&
	__atime) noexcept
	{
	__detail::__bare_timed_wait __w{__addr};
	return __w._M_do_wait_until(__pred, __atime);
	}

	template<typename _Tp, typename _ValFn,
	typename _Rep, typename _Period>
	bool
	__atomic_wait_address_for_v(const _Tp* __addr, _Tp&& __old, _ValFn&& __vfn,
	const chrono::duration<_Rep, _Period>& __rtime) noexcept
	{
	__detail::__enters_timed_wait __w{__addr};
	return __w._M_do_wait_for_v(__old, __vfn, __rtime);
	}

	template<typename _Tp, typename _Pred,
	typename _Rep, typename _Period>
	bool
	__atomic_wait_address_for(const _Tp* __addr, _Pred __pred,
	const chrono::duration<_Rep, _Period>& __rtime) noexcept
	{

	__detail::__enters_timed_wait __w{__addr};
	return __w._M_do_wait_for(__pred, __rtime);
	}

	template<typename _Pred,
	typename _Rep, typename _Period>
	bool
	__atomic_wait_address_for_bare(const __detail::__platform_wait_t* __addr,
	_Pred __pred,
	const chrono::duration<_Rep, _Period>& __rtime) noexcept
	{
	__detail::__bare_timed_wait __w{__addr};
	return __w._M_do_wait_for(__pred, __rtime);
	}
	_GLIBCXX_END_NAMESPACE_VERSION
	} // namespace std
	#endif // __cpp_lib_atomic_wait
	#endif // _GLIBCXX_ATOMIC_TIMED_WAIT_H