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.Dd April 16, 2013 29.Dt SEM_WAIT 3 30.Os 31.Sh NAME 32.Nm sem_wait , 33.Nm sem_trywait 34.Nd decrement (lock) a semaphore 35.Sh LIBRARY 36.Lb libc 37.Sh SYNOPSIS 38.In semaphore.h 39.Ft int 40.Fn sem_wait "sem_t *sem" 41.Ft int 42.Fn sem_trywait "sem_t *sem" 43.Sh DESCRIPTION 44The 45.Fn sem_wait 46function decrements (locks) the semaphore pointed to by 47.Fa sem , 48but blocks if the value of 49.Fa sem 50is zero, until the value is non-zero and the value can be decremented. 51.Pp 52The 53.Fn sem_trywait 54function decrements (locks) the semaphore pointed to by 55.Fa sem 56only if the value is non-zero. 57Otherwise, the semaphore is not decremented and 58an error is returned. 59.Sh RETURN VALUES 60.Rv -std 61.Sh ERRORS 62The 63.Fn sem_wait 64and 65.Fn sem_trywait 66functions will fail if: 67.Bl -tag -width Er 68.It Bq Er EINVAL 69The 70.Fa sem 71argument 72points to an invalid semaphore. 73.El 74.Pp 75Additionally, 76.Fn sem_wait 77will fail if: 78.Bl -tag -width Er 79.It Bq Er EINTR 80A signal interrupted this function. 81.El 82.Pp 83Additionally, 84.Fn sem_trywait 85will fail if: 86.Bl -tag -width Er 87.It Bq Er EAGAIN 88The semaphore value was zero, and thus could not be decremented. 89.El 90.Sh SEE ALSO 91.Xr sem_getvalue 3 , 92.Xr sem_post 3 , 93.Xr sem_timedwait 3 94.Sh STANDARDS 95The 96.Fn sem_wait 97and 98.Fn sem_trywait 99functions conform to 100.St -p1003.1-96 . 101