1.\" $OpenBSD: sem_open.3,v 1.12 2023/02/11 21:13:56 jmc Exp $ 2.\" 3.\" Copyright (c) 2013 Ted Unangst <tedu@openbsd.org> 4.\" 5.\" Permission to use, copy, modify, and distribute this software for any 6.\" purpose with or without fee is hereby granted, provided that the above 7.\" copyright notice and this permission notice appear in all copies. 8.\" 9.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16.\" 17.Dd $Mdocdate: February 11 2023 $ 18.Dt SEM_OPEN 3 19.Os 20.Sh NAME 21.Nm sem_open , 22.Nm sem_close , 23.Nm sem_unlink 24.Nd open and close named semaphores 25.Sh SYNOPSIS 26.In semaphore.h 27.Ft sem_t * 28.Fn sem_open "const char *name" "int oflag" "..." 29.Ft int 30.Fn sem_close "sem_t *sem" 31.Ft int 32.Fn sem_unlink "const char *name" 33.Sh DESCRIPTION 34The 35.Fn sem_open 36function opens and returns a named semaphore. 37The 38.Fn sem_close 39function closes a previously opened named semaphore without removing it. 40The 41.Fn sem_unlink 42function removes the named semaphore from the system without closing it. 43.Sh RETURN VALUES 44On success, 45.Fn sem_open 46returns a pointer to a semaphore. 47.Fn sem_close 48and 49.Fn sem_unlink 50return 0 on success. 51.Fn sem_open 52returns SEM_FAILED and sets 53.Va errno 54to indicate an error. 55.Fn sem_close 56and 57.Fn sem_unlink 58return -1 and set 59.Va errno 60to indicate an error. 61.Sh ERRORS 62It is an error to call 63.Fn sem_close 64with an unnamed semaphore or to call 65.Xr sem_destroy 3 66with a named semaphore. 67.Pp 68.Fn sem_open 69may fail if: 70.Bl -tag -width Er 71.It Bq Er ENOSPC 72Insufficient memory is available. 73.It Bq Er EPERM 74An attempt was made to open a shared semaphore owned by another user. 75.El 76.Pp 77.Fn sem_unlink 78may fail for any of the reasons listed in 79.Xr unlink 2 . 80.Sh SEE ALSO 81.Xr sem_destroy 3 , 82.Xr sem_getvalue 3 , 83.Xr sem_init 3 , 84.Xr sem_post 3 , 85.Xr sem_wait 3 86.Sh STANDARDS 87.Fn sem_open , 88.Fn sem_close , 89and 90.Fn sem_unlink 91appear in 92.St -p1003.1-96 . 93This implementation deviates from the standard by permitting less sharing. 94