condition_variable
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// <condition_variable> -*- C++ -*-
// Copyright (C) 2008-2025 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 include/condition_variable
* This is a Standard C++ Library header.
*/
#ifndef _GLIBCXX_CONDITION_VARIABLE
#define _GLIBCXX_CONDITION_VARIABLE 1
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
#include <bits/requires_hosted.h> // threading primitive
#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else
#include <bits/chrono.h>
#include <bits/error_constants.h>
#include <bits/std_mutex.h>
#include <bits/unique_lock.h>
#include <bits/alloc_traits.h>
#include <bits/shared_ptr.h>
#include <bits/cxxabi_forced.h>
#if __cplusplus > 201703L
# include <stop_token>
#endif
#if defined(_GLIBCXX_HAS_GTHREADS)
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* @defgroup condition_variables Condition Variables
* @ingroup concurrency
*
* Classes for condition_variable support.
* @{
*/
/// cv_status
enum class cv_status { no_timeout, timeout };
/// condition_variable
class condition_variable
{
using steady_clock = chrono::steady_clock;
using system_clock = chrono::system_clock;
#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
using __clock_t = steady_clock;
#else
using __clock_t = system_clock;
#endif
__condvar _M_cond;
public:
typedef __gthread_cond_t* native_handle_type;
condition_variable() noexcept;
~condition_variable() noexcept;
condition_variable(const condition_variable&) = delete;
condition_variable& operator=(const condition_variable&) = delete;
void
notify_one() noexcept;
void
notify_all() noexcept;
void
wait(unique_lock<mutex>& __lock);
template<typename _Predicate>
void
wait(unique_lock<mutex>& __lock, _Predicate __p)
{
while (!__p())
wait(__lock);
}
#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
template<typename _Duration>
cv_status
wait_until(unique_lock<mutex>& __lock,
const chrono::time_point<steady_clock, _Duration>& __atime)
{ return __wait_until_impl(__lock, __atime); }
#endif
template<typename _Duration>
cv_status
wait_until(unique_lock<mutex>& __lock,
const chrono::time_point<system_clock, _Duration>& __atime)
{ return __wait_until_impl(__lock, __atime); }
template<typename _Clock, typename _Duration>
cv_status
wait_until(unique_lock<mutex>& __lock,
const chrono::time_point<_Clock, _Duration>& __atime)
{
#if __cplusplus > 201703L
static_assert(chrono::is_clock_v<_Clock>);
#endif
using __s_dur = typename __clock_t::duration;
const typename _Clock::time_point __c_entry = _Clock::now();
const __clock_t::time_point __s_entry = __clock_t::now();
const auto __delta = __atime - __c_entry;
const auto __s_atime = __s_entry +
chrono::__detail::ceil<__s_dur>(__delta);
if (__wait_until_impl(__lock, __s_atime) == cv_status::no_timeout)
return cv_status::no_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)
return cv_status::no_timeout;
return cv_status::timeout;
}
template<typename _Clock, typename _Duration, typename _Predicate>
bool
wait_until(unique_lock<mutex>& __lock,
const chrono::time_point<_Clock, _Duration>& __atime,
_Predicate __p)
{
while (!__p())
if (wait_until(__lock, __atime) == cv_status::timeout)
return __p();
return true;
}
template<typename _Rep, typename _Period>
cv_status
wait_for(unique_lock<mutex>& __lock,
const chrono::duration<_Rep, _Period>& __rtime)
{
using __dur = typename steady_clock::duration;
return wait_until(__lock,
steady_clock::now() +
chrono::__detail::ceil<__dur>(__rtime));
}
template<typename _Rep, typename _Period, typename _Predicate>
bool
wait_for(unique_lock<mutex>& __lock,
const chrono::duration<_Rep, _Period>& __rtime,
_Predicate __p)
{
using __dur = typename steady_clock::duration;
return wait_until(__lock,
steady_clock::now() +
chrono::__detail::ceil<__dur>(__rtime),
std::move(__p));
}
native_handle_type
native_handle()
{ return _M_cond.native_handle(); }
private:
#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
template<typename _Dur>
cv_status
__wait_until_impl(unique_lock<mutex>& __lock,
const chrono::time_point<steady_clock, _Dur>& __atime)
{
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())
};
_M_cond.wait_until(*__lock.mutex(), CLOCK_MONOTONIC, __ts);
return (steady_clock::now() < __atime
? cv_status::no_timeout : cv_status::timeout);
}
#endif
template<typename _Dur>
cv_status
__wait_until_impl(unique_lock<mutex>& __lock,
const chrono::time_point<system_clock, _Dur>& __atime)
{
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())
};
_M_cond.wait_until(*__lock.mutex(), __ts);
return (system_clock::now() < __atime
? cv_status::no_timeout : cv_status::timeout);
}
};
void
notify_all_at_thread_exit(condition_variable&, unique_lock<mutex>);
struct __at_thread_exit_elt
{
__at_thread_exit_elt* _M_next;
void (*_M_cb)(void*);
};
_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
/// condition_variable_any
// Like above, but mutex is not required to have try_lock.
class condition_variable_any
{
#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
using __clock_t = chrono::steady_clock;
#else
using __clock_t = chrono::system_clock;
#endif
condition_variable _M_cond;
shared_ptr<mutex> _M_mutex;
// scoped unlock - unlocks in ctor, re-locks in dtor
template<typename _Lock>
struct _Unlock
{
explicit _Unlock(_Lock& __lk) : _M_lock(__lk) { __lk.unlock(); }
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
~_Unlock() noexcept(false)
{
if (uncaught_exception())
{
__try
{ _M_lock.lock(); }
__catch(const __cxxabiv1::__forced_unwind&)
{ __throw_exception_again; }
__catch(...)
{ }
}
else
_M_lock.lock();
}
#pragma GCC diagnostic pop
_Unlock(const _Unlock&) = delete;
_Unlock& operator=(const _Unlock&) = delete;
_Lock& _M_lock;
};
public:
condition_variable_any() : _M_mutex(std::make_shared<mutex>()) { }
~condition_variable_any() = default;
condition_variable_any(const condition_variable_any&) = delete;
condition_variable_any& operator=(const condition_variable_any&) = delete;
void
notify_one() noexcept
{
lock_guard<mutex> __lock(*_M_mutex);
_M_cond.notify_one();
}
void
notify_all() noexcept
{
lock_guard<mutex> __lock(*_M_mutex);
_M_cond.notify_all();
}
template<typename _Lock>
void
wait(_Lock& __lock)
{
shared_ptr<mutex> __mutex = _M_mutex;
unique_lock<mutex> __my_lock(*__mutex);
_Unlock<_Lock> __unlock(__lock);
// *__mutex must be unlocked before re-locking __lock so move
// ownership of *__mutex lock to an object with shorter lifetime.
unique_lock<mutex> __my_lock2(std::move(__my_lock));
_M_cond.wait(__my_lock2);
}
template<typename _Lock, typename _Predicate>
void
wait(_Lock& __lock, _Predicate __p)
{
while (!__p())
wait(__lock);
}
template<typename _Lock, typename _Clock, typename _Duration>
cv_status
wait_until(_Lock& __lock,
const chrono::time_point<_Clock, _Duration>& __atime)
{
shared_ptr<mutex> __mutex = _M_mutex;
unique_lock<mutex> __my_lock(*__mutex);
_Unlock<_Lock> __unlock(__lock);
// *__mutex must be unlocked before re-locking __lock so move
// ownership of *__mutex lock to an object with shorter lifetime.
unique_lock<mutex> __my_lock2(std::move(__my_lock));
return _M_cond.wait_until(__my_lock2, __atime);
}
template<typename _Lock, typename _Clock,
typename _Duration, typename _Predicate>
bool
wait_until(_Lock& __lock,
const chrono::time_point<_Clock, _Duration>& __atime,
_Predicate __p)
{
while (!__p())
if (wait_until(__lock, __atime) == cv_status::timeout)
return __p();
return true;
}
template<typename _Lock, typename _Rep, typename _Period>
cv_status
wait_for(_Lock& __lock, const chrono::duration<_Rep, _Period>& __rtime)
{ return wait_until(__lock, __clock_t::now() + __rtime); }
template<typename _Lock, typename _Rep,
typename _Period, typename _Predicate>
bool
wait_for(_Lock& __lock,
const chrono::duration<_Rep, _Period>& __rtime, _Predicate __p)
{ return wait_until(__lock, __clock_t::now() + __rtime, std::move(__p)); }
#ifdef __glibcxx_jthread
template <class _Lock, class _Predicate>
bool wait(_Lock& __lock,
stop_token __stoken,
_Predicate __p)
{
if (__stoken.stop_requested())
{
return __p();
}
std::stop_callback __cb(__stoken, [this] { notify_all(); });
shared_ptr<mutex> __mutex = _M_mutex;
while (!__p())
{
unique_lock<mutex> __my_lock(*__mutex);
if (__stoken.stop_requested())
{
return false;
}
// *__mutex must be unlocked before re-locking __lock so move
// ownership of *__mutex lock to an object with shorter lifetime.
_Unlock<_Lock> __unlock(__lock);
unique_lock<mutex> __my_lock2(std::move(__my_lock));
_M_cond.wait(__my_lock2);
}
return true;
}
template <class _Lock, class _Clock, class _Duration, class _Predicate>
bool wait_until(_Lock& __lock,
stop_token __stoken,
const chrono::time_point<_Clock, _Duration>& __abs_time,
_Predicate __p)
{
if (__stoken.stop_requested())
{
return __p();
}
std::stop_callback __cb(__stoken, [this] { notify_all(); });
shared_ptr<mutex> __mutex = _M_mutex;
while (!__p())
{
bool __stop;
{
unique_lock<mutex> __my_lock(*__mutex);
if (__stoken.stop_requested())
{
return false;
}
_Unlock<_Lock> __u(__lock);
unique_lock<mutex> __my_lock2(std::move(__my_lock));
const auto __status = _M_cond.wait_until(__my_lock2, __abs_time);
__stop = (__status == std::cv_status::timeout) || __stoken.stop_requested();
}
if (__stop)
{
return __p();
}
}
return true;
}
template <class _Lock, class _Rep, class _Period, class _Predicate>
bool wait_for(_Lock& __lock,
stop_token __stoken,
const chrono::duration<_Rep, _Period>& __rel_time,
_Predicate __p)
{
auto __abst = std::chrono::steady_clock::now() + __rel_time;
return wait_until(__lock,
std::move(__stoken),
__abst,
std::move(__p));
}
#endif
};
_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
/// @} group condition_variables
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif // _GLIBCXX_HAS_GTHREADS
#endif // C++11
#endif // _GLIBCXX_CONDITION_VARIABLE
stop_token
cxxabi_forced.h
unique_lock.h
c++0x_warning.h
chrono.h
std::chrono::__detail::ceil
constexpr __enable_if_is_duration< _ToDur > ceil(const duration< _Rep, _Period > &__d)
Definition chrono.h:412
std_mutex.h
requires_hosted.h
error_constants.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::duration_cast
constexpr __enable_if_is_duration< _ToDur > duration_cast(const duration< _Rep, _Period > &__d)
Definition chrono.h:279
std::cv_status
cv_status
cv_status
Definition condition_variable:69
std::shared_ptr::make_shared
shared_ptr< _NonArray< _Tp > > make_shared(_Args &&... __args)
Create an object that is owned by a shared_ptr.
Definition bits/shared_ptr.h:1003
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::condition_variable
condition_variable
Definition condition_variable:73
std::stop_token
Allow testing whether a stop request has been made on a stop_source.
Definition stop_token:56
std::stop_callback
A wrapper for callbacks to be run when a stop request is made.
Definition stop_token:576
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
std::chrono::system_clock
System clock.
Definition chrono.h:1231
std::chrono::steady_clock
Monotonic clock.
Definition chrono.h:1273
__cxxabiv1::__forced_unwind
Thrown as part of forced unwinding.
Definition cxxabi_forced.h:51
std::shared_ptr
A smart pointer with reference-counted copy semantics.
Definition bits/shared_ptr.h:176
std::lock_guard
A simple scoped lock type.
Definition std_mutex.h:246
std::unique_lock
A movable scoped lock type.
Definition unique_lock.h:63
alloc_traits.h
shared_ptr.h