1.\" Copyright (C) 2000 Jason Evans <jasone@FreeBSD.org>. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice(s), this list of conditions and the following disclaimer as 9.\" the first lines of this file unmodified other than the possible 10.\" addition of one or more copyright notices. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice(s), this list of conditions and the following disclaimer in 13.\" the documentation and/or other materials provided with the 14.\" distribution. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 17.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 19.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE 20.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 21.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 22.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR 23.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 24.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE 25.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, 26.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27.\" 28.\" $FreeBSD: src/lib/libc_r/man/sem_init.3,v 1.1.2.9 2001/12/17 10:08:26 ru Exp $ 29.\" 30.Dd June 30, 2009 31.Dt SEM_INIT 3 32.Os 33.Sh NAME 34.Nm sem_init 35.Nd initialize an unnamed semaphore 36.Sh LIBRARY 37.Lb libpthread 38.Sh SYNOPSIS 39.In semaphore.h 40.Ft int 41.Fn sem_init "sem_t *sem" "int pshared" "unsigned int value" 42.Sh DESCRIPTION 43The 44.Fn sem_init 45function initializes the unnamed semaphore pointed to by 46.Fa sem 47to have the value 48.Fa value . 49A non-zero value for 50.Fa pshared 51specifies a shared semaphore that can be used by multiple processes 52in addition to threads. 53Any process able to access the related backing memory, typically via 54.Fn fork , 55is allowed to use a semaphore created with a non-zero 56.Fa pshared , 57otherwise only threads may access the semaphore. 58.Pp 59Following a successful call to 60.Fn sem_init , 61.Fa sem 62can be used as an argument in subsequent calls to 63.Fa sem_wait , 64.Fa sem_trywait , 65.Fa sem_post , 66and 67.Fa sem_destroy . 68.Fa sem 69is no longer valid after a successful call to 70.Fa sem_destroy . 71.Sh IMPLEMENTATION NOTES 72Shared sempahores are allocated out of anonymous shared mmapped 73pages. 74Due to lack of clarity in the standard the mechanics of 75destroying such a space are unclear, so 76.Fa sem_destroy 77is currently unable to reclaim such semaphores. 78.Sh RETURN VALUES 79.Rv -std sem_init 80.Sh ERRORS 81.Fn sem_init 82will fail if: 83.Bl -tag -width Er 84.It Bq Er EINVAL 85.Fa value 86exceeds 87.Dv SEM_VALUE_MAX . 88.It Bq Er ENOSPC 89Memory allocation error. 90.El 91.Sh SEE ALSO 92.Xr umtx 2 , 93.Xr sem_destroy 3 , 94.Xr sem_post 3 , 95.Xr sem_trywait 3 , 96.Xr sem_wait 3 97.Sh STANDARDS 98.Fn sem_init 99conforms to 100.St -p1003.1-96 . 101