NetBSD-5.0.2/lib/libpthread/pthread_cond_wait.3

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.\" $NetBSD: pthread_cond_wait.3,v 1.9 2008/05/26 08:43:08 wiz Exp $
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.\" $FreeBSD: src/lib/libpthread/man/pthread_cond_wait.3,v 1.16 2002/09/16 19:29:28 mini Exp $
.\"
.Dd May 26, 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 unblocks 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 unblocks 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
.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 .