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.\" $FreeBSD: release/9.1.0/lib/libc/gen/sem_post.3 147952 2005-07-13 13:15:22Z rwatson $
.\"
.Dd February 15, 2000
.Dt SEM_POST 3
.Os
.Sh NAME
.Nm sem_post
.Nd increment (unlock) a semaphore
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In 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 .
.Pp
The
.Fn sem_post
function is signal-reentrant and may be called within signal handlers.
.Sh RETURN VALUES
.Rv -std sem_post
.Sh ERRORS
The
.Fn sem_post
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa sem
argument
points to an invalid semaphore.
.El
.Sh SEE ALSO
.Xr sem_getvalue 3 ,
.Xr sem_trywait 3 ,
.Xr sem_wait 3 ,
.Xr sem 4
.Sh STANDARDS
The
.Fn sem_post
function conforms to
.St -p1003.1-96 .