atomic_timed_wait.h
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// -*- C++ -*- header.
// Copyright (C) 2020-2025 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
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
#include <bits/atomic_wait.h>
#if __glibcxx_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
functional_hash.h
chrono.h
this_thread_sleep.h
atomic_wait.h
std::chrono::time_point_cast
constexpr __enable_if_t< __is_duration< _ToDur >::value, time_point< _Clock, _ToDur > > time_point_cast(const time_point< _Clock, _Dur > &__t)
Definition chrono.h:1023
std::chrono::ceil
constexpr __enable_if_is_duration< _ToDur > ceil(const duration< _Rep, _Period > &__d)
Definition chrono.h:412
std::chrono::duration_cast
constexpr __enable_if_is_duration< _ToDur > duration_cast(const duration< _Rep, _Period > &__d)
Definition chrono.h:279
std::move
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition move.h:138
std
ISO C++ entities toplevel namespace is std.
std::__detail
Implementation details not part of the namespace std interface.
std::chrono::duration
chrono::duration represents a distance between two points in time
Definition chrono.h:516
std::chrono::time_point
chrono::time_point represents a point in time as measured by a clock
Definition chrono.h:927