atomic_timed_wait.h

Go to the documentation of this file.

// -*- 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/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;
        if constexpr (is_same_v<__w_dur, _Dur>)
          return __atime;
        else
          return chrono::ceil<__w_dur>(__atime);
      }
 
    // This uses a nanoseconds duration for the timeout argument.
    // For __abi_version=0 that is the time since the steady_clock's epoch.
    // It's possible that in future we will add new __wait_flags constants
    // to indicate that the timeout is the time since the system_clock epoch,
    // or is a relative timeout not an absolute time.
    __wait_result_type
    __wait_until_impl(const void* __addr, __wait_args_base& __args,
                      const chrono::nanoseconds& __timeout);
 
    template<typename _Clock, typename _Dur>
      __wait_result_type
      __wait_until(const void* __addr, __wait_args_base& __args,
                   const chrono::time_point<_Clock, _Dur>& __atime) noexcept
      {
        auto __at = __detail::__to_wait_clock(__atime);
        auto __res = __detail::__wait_until_impl(__addr, __args,
                                                 __at.time_since_epoch());
 
        if constexpr (!is_same_v<__wait_clock_t, _Clock>)
          if (__res._M_timeout)
            {
              // 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)
                __res._M_timeout = false;
            }
        return __res;
      }
 
    template<typename _Rep, typename _Period>
      __wait_result_type
      __wait_for(const void* __addr, __wait_args_base& __args,
                 const chrono::duration<_Rep, _Period>& __rtime) noexcept
      {
        if (!__rtime.count())
          {
            // no rtime supplied, just spin a bit
            __args._M_flags |= __wait_flags::__do_spin | __wait_flags::__spin_only;
            return __detail::__wait_impl(__addr, __args);
          }
 
        auto const __reltime = chrono::ceil<__wait_clock_t::duration>(__rtime);
        auto const __atime = chrono::steady_clock::now() + __reltime;
        return __detail::__wait_until(__addr, __args, __atime);
      }
  } // namespace __detail
 
  // returns true if wait ended before timeout
  template<typename _Tp,
           typename _Pred, typename _ValFn,
           typename _Clock, typename _Dur>
    bool
    __atomic_wait_address_until(const _Tp* __addr, _Pred&& __pred,
                                _ValFn&& __vfn,
                                const chrono::time_point<_Clock, _Dur>& __atime,
                                bool __bare_wait = false) noexcept
    {
      __detail::__wait_args __args{ __addr, __bare_wait };
      _Tp __val = __args._M_setup_wait(__addr, __vfn);
      while (!__pred(__val))
        {
          auto __res = __detail::__wait_until(__addr, __args, __atime);
          if (__res._M_timeout)
            return false; // C++26 will also return last observed __val
          __val = __args._M_setup_wait(__addr, __vfn, __res);
        }
      return true; // C++26 will also return last observed __val
    }
 
  template<typename _Clock, typename _Dur>
    bool
    __atomic_wait_address_until_v(const __detail::__platform_wait_t* __addr,
                                  __detail::__platform_wait_t __old,
                                  int __order,
                                  const chrono::time_point<_Clock, _Dur>& __atime,
                                  bool __bare_wait = false) noexcept
    {
      // This function must not be used if __wait_impl might use a proxy wait:
      __glibcxx_assert(__platform_wait_uses_type<__detail::__platform_wait_t>);
 
      __detail::__wait_args __args{ __addr, __old, __order, __bare_wait };
      auto __res = __detail::__wait_until(__addr, __args, __atime);
      return !__res._M_timeout; // C++26 will also return last observed __val
    }
 
  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,
                                  bool __bare_wait = false) noexcept
    {
      auto __pfn = [&](const _Tp& __val) {
        return !__detail::__atomic_eq(__old, __val);
      };
      return std::__atomic_wait_address_until(__addr, __pfn, __vfn, __atime,
                                              __bare_wait);
    }
 
  template<typename _Tp,
           typename _Pred, typename _ValFn,
           typename _Rep, typename _Period>
    bool
    __atomic_wait_address_for(const _Tp* __addr, _Pred&& __pred,
                              _ValFn&& __vfn,
                              const chrono::duration<_Rep, _Period>& __rtime,
                              bool __bare_wait = false) noexcept
    {
      __detail::__wait_args __args{ __addr, __bare_wait };
      _Tp __val = __args._M_setup_wait(__addr, __vfn);
      while (!__pred(__val))
        {
          auto __res = __detail::__wait_for(__addr, __args, __rtime);
          if (__res._M_timeout)
            return false; // C++26 will also return last observed __val
          __val = __args._M_setup_wait(__addr, __vfn);
        }
      return true; // C++26 will also return last observed __val
    }
 
  template<typename _Rep, typename _Period>
    bool
    __atomic_wait_address_for_v(const __detail::__platform_wait_t* __addr,
                                __detail::__platform_wait_t __old,
                                int __order,
                                const chrono::duration<_Rep, _Period>& __rtime,
                                bool __bare_wait = false) noexcept
    {
      // This function must not be used if __wait_impl might use a proxy wait:
      __glibcxx_assert(__platform_wait_uses_type<__detail::__platform_wait_t>);
 
      __detail::__wait_args __args{ __addr, __old, __order, __bare_wait };
      auto __res = __detail::__wait_for(__addr, __args, __rtime);
      return !__res._M_timeout; // C++26 will also return last observed __val
    }
 
  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,
                                bool __bare_wait = false) noexcept
    {
      auto __pfn = [&](const _Tp& __val) {
        return !__detail::__atomic_eq(__old, __val);
      };
      return __atomic_wait_address_for(__addr, __pfn, forward<_ValFn>(__vfn),
                                       __rtime, __bare_wait);
    }
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // __cpp_lib_atomic_wait
#endif // _GLIBCXX_ATOMIC_TIMED_WAIT_H