\" $NetBSD: sem_wait.3,v 1.3 2012/03/08 22:13:32 wiz Exp $

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Dd February 29, 2012
Dt SEM_WAIT 3
Os
Sh NAME
Nm sem_wait ,
Nm sem_timedwait ,
Nm sem_trywait
Nd decrement (lock) a semaphore
Sh LIBRARY
Lb librt
Sh SYNOPSIS
In semaphore.h
Ft int
Fn sem_wait "sem_t *sem"
Ft int
Fn sem_timedwait "sem_t *sem" "const struct timespec * restrict abstime"
Ft int
Fn sem_trywait "sem_t *sem"
Sh DESCRIPTION
The
Fn sem_wait
function decrements (locks) the semaphore pointed to by
Fa sem ,
but blocks if the value of
Fa sem
is zero, until the value is non-zero and the value can be decremented.
Pp
The
Fn sem_timedwait
function performs the same action, but will not wait beyond
Fa abstime
for the value of
Fa sem
to be non-zero.
Pp
The
Fn sem_trywait
function decrements (locks) the semaphore pointed to by
Fa sem
only if the value is non-zero.
Otherwise, the semaphore is not decremented and an error is returned.
Sh RETURN VALUES
Rv -std sem_wait
Sh ERRORS
Fn sem_wait ,
Fn sem_timedwait ,
and
Fn sem_trywait
will fail if:
Bl -tag -width Er
It Bq Er EINVAL
Fa sem
points to an invalid semaphore.
El
Pp
Additionally,
Fn sem_trywait
will fail if:
Bl -tag -width Er
It Bq Er EAGAIN
The semaphore value was zero, and thus could not be decremented.
El
Pp
Fn sem_timedwait
will also fail if:
Bl -tag -width Er
It Bq Er ETIMEDOUT
The semaphore value was zero and
Fa abstime
was reached.
El
Sh SEE ALSO
Xr sem_post 3
Sh STANDARDS
Fn sem_wait
and
Fn sem_trywait
conform to
St -p1003.1-96 .