1pthread_cond_wait(3C) Standard C Library Functions pthread_cond_wait(3C)
2
6 pthread_cond_wait, pthread_cond_timedwait, pthread_cond_reltimedwait_np
7 - wait on a condition
8
10 cc -mt [ flag... ] file... -lpthread [ library... ]
11 #include <pthread.h>
12 int pthread_cond_wait(pthread_cond_t *restrict cond,
14 pthread_mutex_t *restrict mutex);
15 int pthread_cond_timedwait(pthread_cond_t *restrict cond,
18 pthread_mutex_t *restrict mutex,
19 const struct timespec *restrict abstime);
20 int pthread_cond_reltimedwait_np(pthread_cond_t *cond,
23 pthread_mutex_t *mutex, const struct timespec *reltime);
24
27 The pthread_cond_wait(), pthread_cond_timedwait(), and
28 pthread_cond_reltimedwait_np() functions are used to block on a condi‐
29 tion variable. They are called with mutex locked by the calling thread
30 or undefined behavior will result.
31 These functions atomically release mutex and cause the calling thread
34 to block on the condition variable cond. Atomically here means ``atomi‐
35 cally with respect to access by another thread to the mutex and then
36 the condition variable." That is, if another thread is able to acquire
37 the mutex after the about-to-block thread has released it, then a sub‐
38 sequent call to pthread_cond_signal() or pthread_cond_broadcast() in
39 that thread behaves as if it were issued after the about-to-block
40 thread has blocked.
41 Upon successful return, the mutex has been locked and is owned by the
44 calling thread. If mutex is a robust mutex where an owner terminated
45 while holding the lock and the state is recoverable, the mutex is
46 acquired even though the function returns an error value.
47 When using condition variables there is always a boolean predicate, an
50 invariant, associated with each condition wait that must be true before
51 the thread should proceed. Spurious wakeups from the
52 pthread_cond_wait(), pthread_cond_timedwait(), or pthread_cond_rel‐
53 timedwait_np() functions could occur. Since the return from
54 pthread_cond_wait(), pthread_cond_timedwait(), or pthread_cond_rel‐
55 timedwait_np() does not imply anything about the value of this predi‐
56 cate, the predicate should always be reevaluated.
57 The order in which blocked threads are awakened by pthread_cond_sig‐
60 nal() or pthread_cond_broadcast() is determined by the scheduling pol‐
61 icy. See pthreads(5).
62 The effect of using more than one mutex for concurrent
65 pthread_cond_wait(), pthread_cond_timedwait(), or pthread_cond_rel‐
66 timedwait_np() operations on the same condition variable will result in
67 undefined behavior.
68 A condition wait (whether timed or not) is a cancellation point. When
71 the cancelability enable state of a thread is set to PTHREAD_CAN‐
72 CEL_DEFERRED, a side effect of acting upon a cancellation request while
73 in a condition wait is that the mutex is reacquired before calling the
74 first cancellation cleanup handler.
75 A thread that has been unblocked because it has been canceled while
78 blocked in a call to pthread_cond_wait() or pthread_cond_timedwait()
79 does not consume any condition signal that may be directed concurrently
80 at the condition variable if there are other threads blocked on the
81 condition variable.
82 The pthread_cond_timedwait() function is the same as
85 pthread_cond_wait() except that an error is returned if the absolute
86 time specified by abstime passes (that is, system time equals or
87 exceeds abstime) before the condition cond is signaled or broadcast, or
88 if the absolute time specified by abstime has already been passed at
89 the time of the call. The abstime argument is of type struct timespec,
90 defined in time.h(3HEAD). When such time-outs occur,
91 pthread_cond_timedwait() will nonetheless release and reacquire the
92 mutex referenced by mutex. The function pthread_cond_timedwait() is
93 also a cancellation point.
94 The pthread_cond_reltimedwait_np() function is a non-standard extension
97 provided by the Solaris version of POSIX threads as indicated by the
98 ``_np'' (non-portable) suffix. The pthread_cond_reltimedwait_np() func‐
99 tion is the same as pthread_cond_timedwait() except that the reltime
100 argument specifies a non-negative time relative to the current system
101 time rather than an absolute time. The reltime argument is of type
102 struct timespec, defined in time.h(3HEAD). An error value is returned
103 if the relative time passes (that is, system time equals or exceeds the
104 starting system time plus the relative time) before the condition cond
105 is signaled or broadcast. When such timeouts occur, pthread_cond_rel‐
106 timedwait_np() releases and reacquires the mutex referenced by mutex.
107 The pthread_cond_reltimedwait_np() function is also a cancellation
108 point.
109 If a signal is delivered to a thread waiting for a condition variable,
112 upon return from the signal handler the thread resumes waiting for the
113 condition variable as if it was not interrupted, or it returns 0 due to
114 spurious wakeup.
115
117 Except in the case of ETIMEDOUT, EOWNERDEAD, or ENOTRECOVERABLE, all of
118 these error checks act as if they were performed immediately at the
119 beginning of processing for the function and cause an error return, in
120 effect, prior to modifying the state of the mutex specified by mutex or
121 the condition variable specified by cond.
122 Upon successful completion, 0 is returned. Otherwise, an error value is
125 returned to indicate the error.
126
128 These functions will fail if:
129 EPERM The mutex type is PTHREAD_MUTEX_ERRORCHECK or the mutex is a
131 robust mutex, and the current thread does not own the mutex.
132 The pthread_cond_timedwait() function will fail if:
136 ETIMEDOUT The absolute time specified by abstime to
138 pthread_cond_timedwait() has passed.
139 The pthread_cond_reltimedwait_np() function will fail if:
143 EINVAL The value specified by reltime is invalid.
145 ETIMEDOUT The relative time specified by reltime to
148 pthread_cond_reltimedwait_np() has passed.
149 These functions may fail if:
153 EINVAL The value specified by cond, mutex, abstime, or reltime is
155 invalid.
156 EINVAL Different mutexes were supplied for concurrent operations on
159 the same condition variable.
160 If the mutex specified by mutex is a robust mutex (initialized with the
164 robustness attribute PTHREAD_MUTEX_ROBUST), the pthread_cond_wait(),
165 pthread_cond_timedwait(), and pthread_cond_reltimedwait_np() functions
166 will, under the specified conditions, return the following error val‐
167 ues. For complete information, see the pthread_mutex_lock(3C) and
168 pthread_mutexattr_setrobust(3C) manual pages.
169 EOWNERDEAD The last owner of this mutex died while holding the
171 mutex, leaving the state it was protecting possibly
172 inconsistent. The mutex is now owned by the caller.
173 ENOTRECOVERABLE The mutex was protecting state that has now been
176 left irrecoverable. The mutex has not been acquired.
177
180 See attributes(5) for descriptions of the following attributes:
181 ┌─────────────────────────────┬─────────────────────────────┐
186 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
187 ├─────────────────────────────┼─────────────────────────────┤
188 │Interface Stability │Standard │
189 ├─────────────────────────────┼─────────────────────────────┤
190 │MT-Level │MT-Safe │
191 └─────────────────────────────┴─────────────────────────────┘
192
194 pthread_cond_signal(3C), pthread_cond_broadcast(3C),
195 pthread_mutex_lock(3C), pthread_mutexattr_getrobust(3C), time.h(3HEAD),
196 attributes(5), condition(5), pthreads(5), standards(5)
197SunOS 5.11 11 Nov 2008 pthread_cond_wait(3C)