1.\" $NetBSD: sem_wait.3,v 1.3 2012/03/08 22:13:32 wiz Exp $ 2.\" 3.\" Copyright (C) 2000 Jason Evans <jasone@FreeBSD.org>. 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice(s), this list of conditions and the following disclaimer as 11.\" the first lines of this file unmodified other than the possible 12.\" addition of one or more copyright notices. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice(s), this list of conditions and the following disclaimer in 15.\" the documentation and/or other materials provided with the 16.\" distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 19.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE 22.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR 25.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 26.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE 27.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, 28.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd February 29, 2012 31.Dt SEM_WAIT 3 32.Os 33.Sh NAME 34.Nm sem_wait , 35.Nm sem_timedwait , 36.Nm sem_trywait 37.Nd decrement (lock) a semaphore 38.Sh LIBRARY 39.Lb librt 40.Sh SYNOPSIS 41.In semaphore.h 42.Ft int 43.Fn sem_wait "sem_t *sem" 44.Ft int 45.Fn sem_timedwait "sem_t *sem" "const struct timespec * restrict abstime" 46.Ft int 47.Fn sem_trywait "sem_t *sem" 48.Sh DESCRIPTION 49The 50.Fn sem_wait 51function decrements (locks) the semaphore pointed to by 52.Fa sem , 53but blocks if the value of 54.Fa sem 55is zero, until the value is non-zero and the value can be decremented. 56.Pp 57The 58.Fn sem_timedwait 59function performs the same action, but will not wait beyond 60.Fa abstime 61for the value of 62.Fa sem 63to be non-zero. 64.Pp 65The 66.Fn sem_trywait 67function decrements (locks) the semaphore pointed to by 68.Fa sem 69only if the value is non-zero. 70Otherwise, the semaphore is not decremented and an error is returned. 71.Sh RETURN VALUES 72.Rv -std sem_wait 73.Sh ERRORS 74.Fn sem_wait , 75.Fn sem_timedwait , 76and 77.Fn sem_trywait 78will fail if: 79.Bl -tag -width Er 80.It Bq Er EINVAL 81.Fa sem 82points to an invalid semaphore. 83.El 84.Pp 85Additionally, 86.Fn sem_trywait 87will fail if: 88.Bl -tag -width Er 89.It Bq Er EAGAIN 90The semaphore value was zero, and thus could not be decremented. 91.El 92.Pp 93.Fn sem_timedwait 94will also fail if: 95.Bl -tag -width Er 96.It Bq Er ETIMEDOUT 97The semaphore value was zero and 98.Fa abstime 99was reached. 100.El 101.Sh SEE ALSO 102.Xr sem_post 3 103.Sh STANDARDS 104.Fn sem_wait 105and 106.Fn sem_trywait 107conform to 108.St -p1003.1-96 . 109