.\" $OpenBSD: sem_init.3,v 1.8 2023/02/11 21:13:56 jmc Exp $
.\"
.\" 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: src/lib/libc_r/man/sem_init.3,v 1.11 2001/10/01 16:09:09 ru Exp $
.Dd $Mdocdate: February 11 2023 $
.Dt SEM_INIT 3
.Os
.Sh NAME
.Nm sem_init
.Nd initialize an unnamed semaphore
.Sh SYNOPSIS
.In semaphore.h
.Ft int
.Fn sem_init "sem_t *sem" "int pshared" "unsigned int value"
.Sh DESCRIPTION
The
.Fn sem_init
function initializes the unnamed semaphore pointed to by
.Fa sem
to have the value
.Fa value .
A non-zero value for
.Fa pshared
specifies a shared semaphore that can be used by multiple processes, which this
implementation is not capable of.
.Pp
Following a successful call to
.Fn sem_init ,
.Fa sem
can be used as an argument in subsequent calls to
.Xr sem_wait 3 ,
.Xr sem_trywait 3 ,
.Xr sem_post 3 ,
and
.Xr sem_destroy 3 .
.Fa sem
is no longer valid after a successful call to
.Xr sem_destroy 3 .
.Sh RETURN VALUES
.Rv -std sem_init
.Sh ERRORS
It is an error to call
.Xr sem_destroy 3
on a named semaphore created by
.Xr sem_open 3 .
.Pp
.Fn sem_init
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
.Fa value
exceeds SEM_VALUE_MAX.
.It Bq Er ENOSPC
Memory allocation error.
.It Bq Er EPERM
Unable to initialize a shared semaphore.
.El
.Sh SEE ALSO
.Xr sem_destroy 3 ,
.Xr sem_getvalue 3 ,
.Xr sem_open 3 ,
.Xr sem_post 3 ,
.Xr sem_wait 3
.Sh STANDARDS
.Fn sem_init
conforms to
.St -p1003.1-96 .
.Pp
This implementation does not support shared semaphores, and reports this fact
by setting
.Va errno
to
.Er EPERM .
This is perhaps a stretch of the intention of POSIX, but is
compliant, with the caveat that
.Fn sem_init
always reports a permissions error when an attempt to create a shared semaphore
is made.