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.\" $OpenBSD: sem_open.3,v 1.12 2023/02/11 21:13:56 jmc Exp $
.\"
.\" Copyright (c) 2013 Ted Unangst <tedu@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: February 11 2023 $
.Dt SEM_OPEN 3
.Os
.Sh NAME
.Nm sem_open ,
.Nm sem_close ,
.Nm sem_unlink
.Nd open and close named semaphores
.Sh SYNOPSIS
.In semaphore.h
.Ft sem_t *
.Fn sem_open "const char *name" "int oflag" "..."
.Ft int
.Fn sem_close "sem_t *sem"
.Ft int
.Fn sem_unlink "const char *name"
.Sh DESCRIPTION
The
.Fn sem_open
function opens and returns a named semaphore.
The
.Fn sem_close
function closes a previously opened named semaphore without removing it.
The
.Fn sem_unlink
function removes the named semaphore from the system without closing it.
.Sh RETURN VALUES
On success,
.Fn sem_open
returns a pointer to a semaphore.
.Fn sem_close
and
.Fn sem_unlink
return 0 on success.
.Fn sem_open
returns SEM_FAILED and sets
.Va errno
to indicate an error.
.Fn sem_close
and
.Fn sem_unlink
return -1 and set
.Va errno
to indicate an error.
.Sh ERRORS
It is an error to call
.Fn sem_close
with an unnamed semaphore or to call
.Xr sem_destroy 3
with a named semaphore.
.Pp
.Fn sem_open
may fail if:
.Bl -tag -width Er
.It Bq Er ENOSPC
Insufficient memory is available.
.It Bq Er EPERM
An attempt was made to open a shared semaphore owned by another user.
.El
.Pp
.Fn sem_unlink
may fail for any of the reasons listed in
.Xr unlink 2 .
.Sh SEE ALSO
.Xr sem_destroy 3 ,
.Xr sem_getvalue 3 ,
.Xr sem_init 3 ,
.Xr sem_post 3 ,
.Xr sem_wait 3
.Sh STANDARDS
.Fn sem_open ,
.Fn sem_close ,
and
.Fn sem_unlink
appear in
.St -p1003.1-96 .
This implementation deviates from the standard by permitting less sharing.
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