.\" $OpenBSD: sem_open.3,v 1.12 2023/02/11 21:13:56 jmc Exp $
.\"
.\" Copyright (c) 2013 Ted Unangst <tedu@openbsd.org>
.\"
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.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.