.\" Copyright (C) 2000 Jason Evans <jasone@FreeBSD.org>.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice(s), this list of conditions and the following disclaimer as
.\"    the first lines of this file unmodified other than the possible
.\"    addition of one or more copyright notices.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice(s), this list of conditions and the following disclaimer in
.\"    the documentation and/or other materials provided with the
.\"    distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD: head/lib/libc/gen/sem_post.3 277862 2015-01-28 22:42:56Z jilles $
.\"
.Dd January 28, 2015
.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.
.It Bq Er EOVERFLOW
The semaphore value would exceed
.Dv SEM_VALUE_MAX .
.El
.Sh SEE ALSO
.Xr sem_getvalue 3 ,
.Xr sem_trywait 3 ,
.Xr sem_wait 3
.Sh STANDARDS
The
.Fn sem_post
function conforms to
.St -p1003.1-96 .