.\" $NetBSD: pthread_cond_wait.3,v 1.13 2009/07/02 19:43:06 rumble Exp $ .\" .\" Copyright (c) 2002, 2008 The NetBSD Foundation, Inc. .\" All rights reserved. .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS .\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED .\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR .\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS .\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR .\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF .\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS .\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN .\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE .\" POSSIBILITY OF SUCH DAMAGE. .\" .\" Copyright (c) 1997 Brian Cully .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the author nor the names of any co-contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" $FreeBSD: src/lib/libpthread/man/pthread_cond_wait.3,v 1.16 2002/09/16 19:29:28 mini Exp $ .\" .Dd December 31, 2008 .Dt PTHREAD_COND_WAIT 3 .Os .Sh NAME .Nm pthread_cond_wait , .Nm pthread_cond_timedwait .Nd wait on a condition variable .Sh LIBRARY .Lb libpthread .Sh SYNOPSIS .In pthread.h .Ft int .Fn pthread_cond_wait "pthread_cond_t * restrict cond" "pthread_mutex_t * restrict mutex" .Ft int .Fn pthread_cond_timedwait "pthread_cond_t * restrict cond" "pthread_mutex_t * restrict mutex" "const struct timespec * restrict abstime" .Sh DESCRIPTION The .Fn pthread_cond_wait function atomically blocks the current thread waiting on the condition variable specified by .Fa cond , and unlocks the mutex specified by .Fa mutex . The waiting thread unblocks after another thread calls .Xr pthread_cond_signal 3 , or .Xr pthread_cond_broadcast 3 with the same condition variable. The current thread holds the lock on .Fa mutex upon return from the .Fa pthread_cond_wait call. .Pp The .Fn pthread_cond_timedwait function atomically blocks the current thread waiting on the condition variable specified by .Fa cond , and unlocks the mutex specified by .Fa mutex . The waiting thread unblocks after another thread calls .Xr pthread_cond_signal 3 , or .Xr pthread_cond_broadcast 3 with the same condition variable, or if the system time reaches the time specified in .Fa abstime . .Pp Note that a call to .Fn pthread_cond_wait or .Fn pthread_cond_timedwait may wake up spontaneously, without a call to .Xr pthread_cond_signal 3 or .Xr pthread_cond_broadcast 3 . The caller should prepare for this by invoking .Fn pthread_cond_wait or .Fn pthread_cond_timedwait within a predicate loop that tests whether the thread should proceed. .Pp When calling .Fn pthread_cond_wait or .Fn pthread_cond_timedwait , a temporary binding is established between the condition variable .Fa cond and the mutex .Fa mutex . .Pp The same mutex must be held while calling .Fn pthread_cond_broadcast and .Fn pthread_cond_signal on .Fa cond . Additionally, the same mutex must be used for concurrent calls to .Fn pthread_cond_wait and .Fn pthread_cond_timedwait . Only when a condition variable is known to be quiescent may an application change the mutex associated with it. In this implementation, none of the functions enforce this requirement, but if the mutex is not held or independent mutexes are used the resulting behaviour is undefined. .Sh RETURN VALUES If successful, the .Fn pthread_cond_wait and .Fn pthread_cond_timedwait functions will return zero. Otherwise an error number will be returned to indicate the error. .Sh ERRORS .Fn pthread_cond_wait may fail if: .Bl -tag -width Er .It Bq Er EINVAL The value specified by .Fa cond or the value specified by .Fa mutex is invalid. .El .Pp .Fn pthread_cond_timedwait shall fail if: .Bl -tag -width Er .It Bq Er ETIMEDOUT The system time has reached or exceeded the time specified in .Fa abstime . .El .Pp .Fn pthread_cond_timedwait may fail if: .Bl -tag -width Er .It Bq Er EINVAL The value specified by .Fa cond , .Fa mutex , or .Fa abstime is invalid. .El .Pp .Fn pthread_cond_wait and .Fn pthread_cond_timedwait may fail if: .Bl -tag -width Er .It Bq Er EPERM The value specified by .Fa mutex is not locked in condition wait. .El .Sh SEE ALSO .Xr pthread_cond_broadcast 3 , .Xr pthread_cond_destroy 3 , .Xr pthread_cond_init 3 , .Xr pthread_cond_signal 3 .Sh STANDARDS .Fn pthread_cond_wait and .Fn pthread_cond_timedwait conform to .St -p1003.1-96 .