NetBSD/lib/libpthread/pthread_cond_wait.3

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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 January 30, 2003
.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.
.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 .