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.\" $FreeBSD$ 29.\" 30.Dd December 8, 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 libc 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. 52.Pp 53Following a successful call to 54.Fn sem_init , 55.Fa sem 56can be used as an argument in subsequent calls to 57.Xr sem_wait 3 , 58.Xr sem_trywait 3 , 59.Xr sem_post 3 , 60and 61.Xr sem_destroy 3 . 62The 63.Fa sem 64argument is no longer valid after a successful call to 65.Xr sem_destroy 3 . 66.Sh RETURN VALUES 67.Rv -std sem_init 68.Sh ERRORS 69The 70.Fn sem_init 71function will fail if: 72.Bl -tag -width Er 73.It Bq Er EINVAL 74The 75.Fa value 76argument exceeds 77.Dv SEM_VALUE_MAX . 78.It Bq Er ENOSPC 79Memory allocation error. 80.El 81.Sh SEE ALSO 82.Xr sem_destroy 3 , 83.Xr sem_getvalue 3 , 84.Xr sem_post 3 , 85.Xr sem_trywait 3 , 86.Xr sem_wait 3 , 87.Xr sem 4 88.Sh STANDARDS 89The 90.Fn sem_init 91function conforms to 92.St -p1003.1-96 . 93.Sh BUGS 94A sem_t is a pointer to a separately allocated structure, 95therefore process shared semaphores only work between related processes 96and do not perform very well 97(each operation is a system call, 98while single-process semaphores only do a system call 99if they need to block or wake up a thread). 100