.\" Copyright (c) 2008, David Xu <davidxu@FreeBSD.org>
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.\" Portions of this text are reprinted and reproduced in electronic form
.\" from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology --
.\" Portable Operating System Interface (POSIX), The Open Group Base
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.Dd March 3, 2008
.Dt SEM_TIMEDWAIT 3
.Os
.Sh NAME
.Nm sem_timedwait
.Nd "lock a semaphore"
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In semaphore.h
.Ft int
.Fn sem_timedwait "sem_t *sem" "const struct timespec *abs_timeout"
.Sh DESCRIPTION
The
.Fn sem_timedwait
function locks the semaphore referenced by
.Fa sem ,
as in the
.Xr sem_wait 3
function.
However, if the semaphore cannot be locked without waiting for
another process or thread to unlock the semaphore by performing
a
.Xr sem_post 3
function, this wait will be terminated when the specified timeout expires.
.Pp
The timeout will expire when the absolute time specified by
.Fa abs_timeout
passes, as measured by the clock on which timeouts are based (that is,
when the value of that clock equals or exceeds
.Fa abs_timeout ) ,
or if the
absolute time specified by
.Fa abs_timeout
has already been passed at the time of the call.
.Pp
Note that the timeout is based on the
.Dv CLOCK_REALTIME
clock.
.Pp
The validity of the
.Fa abs_timeout
is not checked if the semaphore can be locked immediately.
.Sh RETURN VALUES
The
.Fn sem_timedwait
function returns zero if the calling process successfully performed the
semaphore lock operation on the semaphore designated by
.Fa sem .
If the call was unsuccessful, the state of the semaphore is unchanged,
and the function returns a value of \-1 and sets the global variable
.Va errno
to indicate the error.
.Sh ERRORS
The
.Fn sem_timedwait
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa sem
argument does not refer to a valid semaphore, or the process or thread would
have blocked, and the
.Fa abs_timeout
parameter specified a nanoseconds field value less than zero or greater than
or equal to 1000 million.
.It Bq Er ETIMEDOUT
The semaphore could not be locked before the specified timeout expired.
.It Bq Er EINTR
A signal interrupted this function.
.El
.Sh SEE ALSO
.Xr sem_post 3 ,
.Xr sem_trywait 3 ,
.Xr sem_wait 3 ,
.Xr sem 4
.Sh STANDARDS
The
.Fn sem_timedwait
function conforms to
.St -p1003.1-2004 .
.Sh HISTORY
The function first appeared in
.Fx 5.0 .