.\" Copyright (C) 2000 Jason Evans <jasone@freebsd.org>.
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.\" $FreeBSD$
.Dd February 15, 2000
.Dt SEM_POST 3
.Os
.Sh NAME
.Nm sem_post
.Nd increment (unlock) a semaphore
.Sh LIBRARY
.Lb libc_r
.Sh SYNOPSIS
.Fd #include <semaphore.h>
.Ft int
.Fn sem_post "sem_t *sem"
.Sh DESCRIPTION
The
.Fn sem_post
function increments (unlocks) the semaphore pointed to by
.Fa sem .
If there are threads blocked on the semaphore when
.Fn sem_post
is called, then the highest priority thread that has been blocked the longest on
the semaphore will be allowed to return from
.Fn sem_wait .
.Sh RETURN VALUES
If successful,
.Fn sem_post
returns 0.  Otherwise, -1 is returned and
.Va errno
is set to indicate the type of
error.
.Sh ERRORS
.Fn sem_post
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
.Fa sem
points to an invalid semaphore.
.El
.Sh SEE ALSO
.Xr sem_trywait 3 ,
.Xr sem_wait 3
.Sh STANDARDS
.Fn sem_post
conforms to ISO/IEC 9945-1 ANSI/IEEE
.Pq Dq Tn POSIX
Std 1003.1 1996 Edition.