libstdc++: condition_variable Source File

libstdc++

condition_variable
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1// <condition_variable> -*- C++ -*-
2
3// Copyright (C) 2008-2026 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library. This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 3, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14// GNU General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23// <http://www.gnu.org/licenses/>.
24
25/** @file include/condition_variable
26 * This is a Standard C++ Library header.
27 */
28
29#ifndef _GLIBCXX_CONDITION_VARIABLE
30#define _GLIBCXX_CONDITION_VARIABLE 1
31
32#ifdef _GLIBCXX_SYSHDR
33#pragma GCC system_header
34#endif
35
36#include <bits/requires_hosted.h> // threading primitive
37
38#if __cplusplus < 201103L
39# include <bits/c++0x_warning.h>
40#else
41
42#include <bits/chrono.h>
43#include <bits/error_constants.h>
44#include <bits/std_mutex.h>
45#include <bits/unique_lock.h>
46#include <bits/alloc_traits.h>
47#include <bits/shared_ptr.h>
48#include <bits/cxxabi_forced.h>
49
50#if __cplusplus > 201703L
51# include <stop_token>
52#endif
53
54#if defined(_GLIBCXX_HAS_GTHREADS)
55
56namespace std _GLIBCXX_VISIBILITY(default)
57{
58_GLIBCXX_BEGIN_NAMESPACE_VERSION
59
60 /**
61 * @defgroup condition_variables Condition Variables
62 * @ingroup concurrency
63 *
64 * Classes for condition_variable support.
65 * @{
66 */
67
68 /// cv_status
69 enum class cv_status { no_timeout, timeout };
70
71 /// condition_variable
72 class condition_variable
73 {
74 using steady_clock = chrono::steady_clock;
75 using system_clock = chrono::system_clock;
76#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
77 using __clock_t = steady_clock;
78#else
79 using __clock_t = system_clock;
80#endif
81
82 __condvar _M_cond;
83
84 public:
85 typedef __gthread_cond_t* native_handle_type;
86
87 condition_variable() noexcept;
88 ~condition_variable() noexcept;
89
90 condition_variable(const condition_variable&) = delete;
91 condition_variable& operator=(const condition_variable&) = delete;
92
93 void
94 notify_one() noexcept;
95
96 void
97 notify_all() noexcept;
98
99 void
100 wait(unique_lock<mutex>& __lock);
101
102 template<typename _Predicate>
103 void
104 wait(unique_lock<mutex>& __lock, _Predicate __p)
105 {
106 while (!__p())
107 wait(__lock);
108 }
109
110#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
111 template<typename _Duration>
112 cv_status
113 wait_until(unique_lock<mutex>& __lock,
114 const chrono::time_point<steady_clock, _Duration>& __atime)
115 { return __wait_until_impl(__lock, __atime); }
116#endif
117
118 template<typename _Duration>
119 cv_status
120 wait_until(unique_lock<mutex>& __lock,
121 const chrono::time_point<system_clock, _Duration>& __atime)
122 { return __wait_until_impl(__lock, __atime); }
123
124 template<typename _Clock, typename _Duration>
125 cv_status
126 wait_until(unique_lock<mutex>& __lock,
127 const chrono::time_point<_Clock, _Duration>& __atime)
128 {
129#if __cplusplus > 201703L
130 static_assert(chrono::is_clock_v<_Clock>);
131#endif
132 using __s_dur = typename __clock_t::duration;
133 const typename _Clock::time_point __c_entry = _Clock::now();
134 const __clock_t::time_point __s_entry = __clock_t::now();
135 const auto __delta = __atime - __c_entry;
136 const auto __s_atime = __s_entry +
137 chrono::__detail::ceil<__s_dur>(__delta);
138
139 if (__wait_until_impl(__lock, __s_atime) == cv_status::no_timeout)
140 return cv_status::no_timeout;
141 // We got a timeout when measured against __clock_t but
142 // we need to check against the caller-supplied clock
143 // to tell whether we should return a timeout.
144 if (_Clock::now() < __atime)
145 return cv_status::no_timeout;
146 return cv_status::timeout;
147 }
148
149 template<typename _Clock, typename _Duration, typename _Predicate>
150 bool
151 wait_until(unique_lock<mutex>& __lock,
152 const chrono::time_point<_Clock, _Duration>& __atime,
153 _Predicate __p)
154 {
155 while (!__p())
156 if (wait_until(__lock, __atime) == cv_status::timeout)
157 return __p();
158 return true;
159 }
160
161 template<typename _Rep, typename _Period>
162 cv_status
163 wait_for(unique_lock<mutex>& __lock,
164 const chrono::duration<_Rep, _Period>& __rtime)
165 {
166 using __dur = typename steady_clock::duration;
167 return wait_until(__lock,
168 steady_clock::now() +
169 chrono::__detail::ceil<__dur>(__rtime));
170 }
171
172 template<typename _Rep, typename _Period, typename _Predicate>
173 bool
174 wait_for(unique_lock<mutex>& __lock,
175 const chrono::duration<_Rep, _Period>& __rtime,
176 _Predicate __p)
177 {
178 using __dur = typename steady_clock::duration;
179 return wait_until(__lock,
180 steady_clock::now() +
181 chrono::__detail::ceil<__dur>(__rtime),
182 std::move(__p));
183 }
184
185 native_handle_type
186 native_handle()
187 { return _M_cond.native_handle(); }
188
189 private:
190#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
191 template<typename _Dur>
192 cv_status
193 __wait_until_impl(unique_lock<mutex>& __lock,
194 const chrono::time_point<steady_clock, _Dur>& __atime)
195 {
196 __gthread_time_t __ts = chrono::__to_timeout_gthread_time_t(__atime);
197 _M_cond.wait_until(*__lock.mutex(), CLOCK_MONOTONIC, __ts);
198
199 return (steady_clock::now() < __atime
200 ? cv_status::no_timeout : cv_status::timeout);
201 }
202#endif
203
204 template<typename _Dur>
205 cv_status
206 __wait_until_impl(unique_lock<mutex>& __lock,
207 const chrono::time_point<system_clock, _Dur>& __atime)
208 {
209 __gthread_time_t __ts = chrono::__to_timeout_gthread_time_t(__atime);
210 _M_cond.wait_until(*__lock.mutex(), __ts);
211
212 return (system_clock::now() < __atime
213 ? cv_status::no_timeout : cv_status::timeout);
214 }
215 };
216
217 void
218 notify_all_at_thread_exit(condition_variable&, unique_lock<mutex>);
219
220 struct __at_thread_exit_elt
221 {
222 __at_thread_exit_elt* _M_next;
223 void (*_M_cb)(void*);
224 };
225
226_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
227
228 /// condition_variable_any
229 // Like above, but mutex is not required to have try_lock.
230 class condition_variable_any
231 {
232#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
233 using __clock_t = chrono::steady_clock;
234#else
235 using __clock_t = chrono::system_clock;
236#endif
237 condition_variable _M_cond;
238 shared_ptr<mutex> _M_mutex;
239
240 // scoped unlock - unlocks in ctor, re-locks in dtor
241 template<typename _Lock>
242 struct _Unlock
243 {
244 explicit _Unlock(_Lock& __lk) : _M_lock(__lk) { __lk.unlock(); }
245
246#pragma GCC diagnostic push
247#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
248 ~_Unlock() noexcept(false)
249 {
250 if (uncaught_exception())
251 {
252 __try
253 { _M_lock.lock(); }
254 __catch(const __cxxabiv1::__forced_unwind&)
255 { __throw_exception_again; }
256 __catch(...)
257 { }
258 }
259 else
260 _M_lock.lock();
261 }
262#pragma GCC diagnostic pop
263
264 _Unlock(const _Unlock&) = delete;
265 _Unlock& operator=(const _Unlock&) = delete;
266
267 _Lock& _M_lock;
268 };
269
270 public:
271 condition_variable_any() : _M_mutex(std::make_shared<mutex>()) { }
272 ~condition_variable_any() = default;
273
274 condition_variable_any(const condition_variable_any&) = delete;
275 condition_variable_any& operator=(const condition_variable_any&) = delete;
276
277 void
278 notify_one() noexcept
279 {
280 lock_guard<mutex> __lock(*_M_mutex);
281 _M_cond.notify_one();
282 }
283
284 void
285 notify_all() noexcept
286 {
287 lock_guard<mutex> __lock(*_M_mutex);
288 _M_cond.notify_all();
289 }
290
291 template<typename _Lock>
292 void
293 wait(_Lock& __lock)
294 {
295 shared_ptr<mutex> __mutex = _M_mutex;
296 unique_lock<mutex> __my_lock(*__mutex);
297 _Unlock<_Lock> __unlock(__lock);
298 // *__mutex must be unlocked before re-locking __lock so move
299 // ownership of *__mutex lock to an object with shorter lifetime.
300 unique_lock<mutex> __my_lock2(std::move(__my_lock));
301 _M_cond.wait(__my_lock2);
302 }
303
304
305 template<typename _Lock, typename _Predicate>
306 void
307 wait(_Lock& __lock, _Predicate __p)
308 {
309 while (!__p())
310 wait(__lock);
311 }
312
313 template<typename _Lock, typename _Clock, typename _Duration>
314 cv_status
315 wait_until(_Lock& __lock,
316 const chrono::time_point<_Clock, _Duration>& __atime)
317 {
318 shared_ptr<mutex> __mutex = _M_mutex;
319 unique_lock<mutex> __my_lock(*__mutex);
320 _Unlock<_Lock> __unlock(__lock);
321 // *__mutex must be unlocked before re-locking __lock so move
322 // ownership of *__mutex lock to an object with shorter lifetime.
323 unique_lock<mutex> __my_lock2(std::move(__my_lock));
324 return _M_cond.wait_until(__my_lock2, __atime);
325 }
326
327 template<typename _Lock, typename _Clock,
328 typename _Duration, typename _Predicate>
329 bool
330 wait_until(_Lock& __lock,
331 const chrono::time_point<_Clock, _Duration>& __atime,
332 _Predicate __p)
333 {
334 while (!__p())
335 if (wait_until(__lock, __atime) == cv_status::timeout)
336 return __p();
337 return true;
338 }
339
340 template<typename _Lock, typename _Rep, typename _Period>
341 cv_status
342 wait_for(_Lock& __lock, const chrono::duration<_Rep, _Period>& __rtime)
343 { return wait_until(__lock, __clock_t::now() + __rtime); }
344
345 template<typename _Lock, typename _Rep,
346 typename _Period, typename _Predicate>
347 bool
348 wait_for(_Lock& __lock,
349 const chrono::duration<_Rep, _Period>& __rtime, _Predicate __p)
350 { return wait_until(__lock, __clock_t::now() + __rtime, std::move(__p)); }
351
352#ifdef __glibcxx_jthread
353 template <class _Lock, class _Predicate>
354 bool wait(_Lock& __lock,
355 stop_token __stoken,
356 _Predicate __p)
357 {
358 if (__stoken.stop_requested())
359 {
360 return __p();
361 }
362
363 std::stop_callback __cb(__stoken, [this] { notify_all(); });
364 shared_ptr<mutex> __mutex = _M_mutex;
365 while (!__p())
366 {
367 unique_lock<mutex> __my_lock(*__mutex);
368 if (__stoken.stop_requested())
369 {
370 return false;
371 }
372 // *__mutex must be unlocked before re-locking __lock so move
373 // ownership of *__mutex lock to an object with shorter lifetime.
374 _Unlock<_Lock> __unlock(__lock);
375 unique_lock<mutex> __my_lock2(std::move(__my_lock));
376 _M_cond.wait(__my_lock2);
377 }
378 return true;
379 }
380
381 template <class _Lock, class _Clock, class _Duration, class _Predicate>
382 bool wait_until(_Lock& __lock,
383 stop_token __stoken,
384 const chrono::time_point<_Clock, _Duration>& __abs_time,
385 _Predicate __p)
386 {
387 if (__stoken.stop_requested())
388 {
389 return __p();
390 }
391
392 std::stop_callback __cb(__stoken, [this] { notify_all(); });
393 shared_ptr<mutex> __mutex = _M_mutex;
394 while (!__p())
395 {
396 bool __stop;
397 {
398 unique_lock<mutex> __my_lock(*__mutex);
399 if (__stoken.stop_requested())
400 {
401 return false;
402 }
403 _Unlock<_Lock> __u(__lock);
404 unique_lock<mutex> __my_lock2(std::move(__my_lock));
405 const auto __status = _M_cond.wait_until(__my_lock2, __abs_time);
406 __stop = (__status == std::cv_status::timeout) || __stoken.stop_requested();
407 }
408 if (__stop)
409 {
410 return __p();
411 }
412 }
413 return true;
414 }
415
416 template <class _Lock, class _Rep, class _Period, class _Predicate>
417 bool wait_for(_Lock& __lock,
418 stop_token __stoken,
419 const chrono::duration<_Rep, _Period>& __rel_time,
420 _Predicate __p)
421 {
422 auto __abst = std::chrono::steady_clock::now() + __rel_time;
423 return wait_until(__lock,
424 std::move(__stoken),
425 __abst,
426 std::move(__p));
427 }
428#endif
429 };
430
431_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
432
433 /// @} group condition_variables
434_GLIBCXX_END_NAMESPACE_VERSION
435} // namespace
436
437#endif // _GLIBCXX_HAS_GTHREADS
438#endif // C++11
439#endif // _GLIBCXX_CONDITION_VARIABLE
stop_token
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
requires_hosted.h
std_mutex.h
unique_lock.h
cxxabi_forced.h
error_constants.h
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:1061
std::move
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition move.h:138
std::uncaught_exception
bool uncaught_exception() noexcept
std
ISO C++ entities toplevel namespace is std.
std::condition_variable
condition_variable
Definition condition_variable:73
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:270
std::unique_lock
A movable scoped lock type.
Definition unique_lock.h:63
alloc_traits.h
shared_ptr.h