1.\" Copyright (c) 2008, David Xu <davidxu@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, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" Portions of this text are reprinted and reproduced in electronic form 26.\" from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology -- 27.\" Portable Operating System Interface (POSIX), The Open Group Base 28.\" Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of 29.\" Electrical and Electronics Engineers, Inc and The Open Group. In the 30.\" event of any discrepancy between this version and the original IEEE and 31.\" The Open Group Standard, the original IEEE and The Open Group Standard is 32.\" the referee document. The original Standard can be obtained online at 33.\" http://www.opengroup.org/unix/online.html. 34.\" 35.\" $FreeBSD: src/lib/libc/gen/sem_timedwait.3,v 1.6 2012/11/17 01:49:25 svnexp Exp $ 36.\" 37.Dd December 25, 2012 38.Dt SEM_TIMEDWAIT 3 39.Os 40.Sh NAME 41.Nm sem_timedwait 42.Nd "lock a semaphore" 43.Sh LIBRARY 44.Lb libpthread 45.Sh SYNOPSIS 46.In semaphore.h 47.Ft int 48.Fn sem_timedwait "sem_t * restrict sem" "const struct timespec * restrict abs_timeout" 49.Sh DESCRIPTION 50The 51.Fn sem_timedwait 52function locks the semaphore referenced by 53.Fa sem , 54as in the 55.Xr sem_wait 3 56function. 57However, if the semaphore cannot be locked without waiting for 58another process or thread to unlock the semaphore by performing 59a 60.Xr sem_post 3 61function, this wait will be terminated when the specified timeout expires. 62.Pp 63The timeout will expire when the absolute time specified by 64.Fa abs_timeout 65passes, as measured by the clock on which timeouts are based (that is, 66when the value of that clock equals or exceeds 67.Fa abs_timeout ) , 68or if the 69absolute time specified by 70.Fa abs_timeout 71has already been passed at the time of the call. 72.Pp 73Note that the timeout is based on the 74.Dv CLOCK_REALTIME 75clock. 76.Pp 77The validity of the 78.Fa abs_timeout 79is not checked if the semaphore can be locked immediately. 80.Sh RETURN VALUES 81The 82.Fn sem_timedwait 83function returns zero if the calling process successfully performed the 84semaphore lock operation on the semaphore designated by 85.Fa sem . 86If the call was unsuccessful, the state of the semaphore is unchanged, 87and the function returns a value of \-1 and sets the global variable 88.Va errno 89to indicate the error. 90.Sh ERRORS 91The 92.Fn sem_timedwait 93function will fail if: 94.Bl -tag -width Er 95.It Bq Er EINVAL 96The 97.Fa sem 98argument does not refer to a valid semaphore, or the process or thread would 99have blocked, and the 100.Fa abs_timeout 101parameter specified a nanoseconds field value less than zero or greater than 102or equal to 1000 million. 103.It Bq Er ETIMEDOUT 104The semaphore could not be locked before the specified timeout expired. 105.It Bq Er EINTR 106A signal interrupted this function. 107.El 108.Sh SEE ALSO 109.Xr sem_post 3 , 110.Xr sem_trywait 3 , 111.Xr sem_wait 3 112.Sh STANDARDS 113The 114.Fn sem_timedwait 115function conforms to 116.St -p1003.1-2004 . 117.Sh HISTORY 118The function first appeared in 119.Fx 5.0 . 120