1.\" $OpenBSD: sem_wait.3,v 1.9 2013/06/05 03:44:50 tedu 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.\" $FreeBSD: src/lib/libc_r/man/sem_wait.3,v 1.8 2001/10/01 16:09:09 ru Exp $ 31.Dd $Mdocdate: June 5 2013 $ 32.Dt SEM_WAIT 3 33.Os 34.Sh NAME 35.Nm sem_wait , 36.Nm sem_timedwait , 37.Nm sem_trywait 38.Nd decrement (lock) a semaphore 39.Sh SYNOPSIS 40.In semaphore.h 41.Ft int 42.Fn sem_wait "sem_t *sem" 43.Ft int 44.Fn sem_timedwait "sem_t *sem" "const struct timespec *abstime" 45.Ft int 46.Fn sem_trywait "sem_t *sem" 47.Sh DESCRIPTION 48The 49.Fn sem_wait 50function decrements (locks) the semaphore pointed to by 51.Fa sem , 52but blocks if the value of 53.Fa sem 54is zero, until the value is non-zero and the value can be decremented. 55.Pp 56The 57.Fn sem_timedwait 58function decrements (locks) the semaphore pointed to by 59.Fa sem , 60but blocks if the value of 61.Fa sem 62is zero, until either the value is non-zero and can be decremented 63or the system time specified by 64.Fa abstime 65is reached. 66.Pp 67The 68.Fn sem_trywait 69function decrements (locks) the semaphore pointed to by 70.Fa sem 71only if the value is non-zero. 72Otherwise, the semaphore is not decremented and 73an error is returned. 74.Sh RETURN VALUES 75.Rv -std sem_wait sem_timedwait sem_trywait 76.Sh ERRORS 77.Fn sem_wait , 78.Fn sem_timedwait , 79and 80.Fn sem_trywait 81will fail if: 82.Bl -tag -width Er 83.It Bq Er EINVAL 84.Fa sem 85points to an invalid semaphore. 86.El 87.Pp 88Additionally, 89.Fn sem_timedwait 90will fail if: 91.Bl -tag -width Er 92.It Bq Er ETIMEDOUT 93The semaphore value was zero and could not be decremented before 94.Fa abstime 95was reached. 96.El 97.Pp 98Additionally, 99.Fn sem_trywait 100will fail if: 101.Bl -tag -width Er 102.It Bq Er EAGAIN 103The semaphore value was zero, and thus could not be decremented. 104.El 105.Sh SEE ALSO 106.Xr sem_destroy 3 , 107.Xr sem_getvalue 3 , 108.Xr sem_init 3 , 109.Xr sem_open 3 , 110.Xr sem_post 3 111.Sh STANDARDS 112.Fn sem_wait , 113.Fn sem_timedwait , 114and 115.Fn sem_trywait 116conform to 117.St -p1003.1-2008 . 118