1.\" $OpenBSD: usleep.3,v 1.17 2008/10/24 14:34:39 jmc Exp $ 2.\" 3.\" Copyright (c) 1986, 1991, 1993 4.\" The Regents of the University of California. 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, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.Dd $Mdocdate: October 24 2008 $ 31.Dt USLEEP 3 32.Os 33.Sh NAME 34.Nm usleep 35.Nd suspend execution for interval of microseconds 36.Sh SYNOPSIS 37.Fd #include <unistd.h> 38.Ft int 39.Fn usleep "useconds_t microseconds" 40.Sh DESCRIPTION 41The 42.Fn usleep 43function suspends execution of the calling process for 44.Fa microseconds 45microseconds of time. 46System activity or time spent in processing the 47call may lengthen the sleep slightly. 48.Pp 49This routine is implemented using 50.Xr nanosleep 2 ; 51it requires one system call each time it is invoked. 52A similar but less compatible function can be obtained with a single 53.Xr select 2 ; 54such a function would not restart after signals, and also does not interfere 55with other uses of 56.Xr setitimer 2 57(not that 58.Fn usleep 59interferes with interval timers anymore). 60.Sh RETURN VALUES 61If the 62.Fn usleep 63function returns because the requested time has elapsed, the value 64returned will be zero. 65.Pp 66If the 67.Fn usleep 68function returns due to the delivery of a signal, the value returned 69will be \-1, and the global variable 70.Va errno 71will be set to indicate the interruption. 72.Sh ERRORS 73If any of the following conditions occur, the 74.Fn usleep 75function shall return \-1 and set 76.Va errno 77to the corresponding value. 78.Bl -tag -width Er 79.It Bq Er EINTR 80.Fn usleep 81was interrupted by the delivery of a signal. 82.It Bq Er EINVAL 83.Fa microseconds 84specified a value of 1,000,000 or more microseconds. 85.El 86.Sh NOTES 87A microsecond is 0.000001 seconds. 88.Sh SEE ALSO 89.Xr sleep 1 , 90.Xr getitimer 2 , 91.Xr nanosleep 2 , 92.Xr setitimer 2 , 93.Xr alarm 3 , 94.Xr sigpause 3 , 95.Xr sleep 3 , 96.Xr ualarm 3 97.Sh STANDARDS 98The 99.Fn usleep 100function conforms to 101.St -xpg4.2 . 102.Sh HISTORY 103The 104.Fn usleep 105function appeared in 106.Bx 4.3 . 107