1.\" $OpenBSD: sem_wait.3,v 1.1 2002/01/28 19:24:03 fgsch Exp $ 2.\" Copyright (C) 2000 Jason Evans <jasone@FreeBSD.org>. 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice(s), this list of conditions and the following disclaimer as 10.\" the first lines of this file unmodified other than the possible 11.\" addition of one or more copyright notices. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice(s), this list of conditions and the following disclaimer in 14.\" the documentation and/or other materials provided with the 15.\" distribution. 16.\" 17.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 18.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 20.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE 21.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 22.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 23.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR 24.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 25.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE 26.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, 27.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28.\" 29.\" $FreeBSD: src/lib/libc_r/man/sem_wait.3,v 1.8 2001/10/01 16:09:09 ru Exp $ 30.Dd February 15, 2000 31.Dt SEM_WAIT 3 32.Os 33.Sh NAME 34.Nm sem_wait , 35.Nm sem_trywait 36.Nd decrement (lock) a semaphore 37.\" .Sh LIBRARY 38.\" .Lb libc_r 39.Sh SYNOPSIS 40.In semaphore.h 41.Ft int 42.Fn sem_wait "sem_t *sem" 43.Ft int 44.Fn sem_trywait "sem_t *sem" 45.Sh DESCRIPTION 46The 47.Fn sem_wait 48function decrements (locks) the semaphore pointed to by 49.Fa sem , 50but blocks if the value of 51.Fa sem 52is zero, until the value is non-zero and the value can be decremented. 53.Pp 54The 55.Fn sem_trywait 56function decrements (locks) the semaphore pointed to by 57.Fa sem 58only if the value is non-zero. Otherwise, the semaphore is not decremented and 59an error is returned. 60.Sh RETURN VALUES 61.Rv -std 62.Sh ERRORS 63.Fn sem_wait 64and 65.Fn sem_trywait 66will fail if: 67.Bl -tag -width Er 68.It Bq Er EINVAL 69.Fa sem 70points to an invalid semaphore. 71.El 72.Pp 73Additionally, 74.Fn sem_trywait 75will fail if: 76.Bl -tag -width Er 77.It Bq Er EAGAIN 78The semaphore value was zero, and thus could not be decremented. 79.El 80.Sh SEE ALSO 81.Xr sem_post 3 82.Sh STANDARDS 83.Fn sem_wait 84and 85.Fn sem_trywait 86conform to 87.St -p1003.1-96 . 88