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.\" $OpenBSD: usleep.3,v 1.16 2007/05/31 19:19:29 jmc Exp $
.\"
.\" Copyright (c) 1986, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd $Mdocdate: May 31 2007 $
.Dt USLEEP 3
.Os
.Sh NAME
.Nm usleep
.Nd suspend execution for interval of microseconds
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn usleep "useconds_t microseconds"
.Sh DESCRIPTION
The
.Fn usleep
function suspends execution of the calling process for
.Fa microseconds
microseconds of time.
System activity or time spent in processing the
call may lengthen the sleep slightly.
.Pp
This routine is implemented using
.Xr nanosleep 2 ;
it requires one system call each time it is invoked.
A similar but less compatible function can be obtained with a single
.Xr select 2 ;
such a function would not restart after signals, and also does not interfere
with other uses of
.Xr setitimer 2
(not that
.Fn usleep
interferes with interval timers anymore).
.Sh RETURN VALUES
If the
.Fn usleep
function returns because the requested time has elapsed, the value
returned will be zero.
.Pp
If the
.Fn usleep
function returns due to the delivery of a signal, the value returned
will be \-1, and the global variable
.Va errno
will be set to indicate the interruption.
.Sh ERRORS
If any of the following conditions occur, the
.Fn usleep
function shall return \-1 and set
.Va errno
to the corresponding value.
.Bl -tag -width Er
.It Bq Er EINTR
.Fn usleep
was interrupted by the delivery of a signal.
.It Bq Er EINVAL
.Fa microseconds
specified a value of 1,000,000 or more microseconds.
.El
.Sh NOTES
A microsecond is 0.000001 seconds.
.Sh SEE ALSO
.Xr getitimer 2 ,
.Xr nanosleep 2 ,
.Xr setitimer 2 ,
.Xr alarm 3 ,
.Xr sigpause 3 ,
.Xr sleep 3 ,
.Xr ualarm 3
.Sh STANDARDS
The
.Fn usleep
function conforms to
.St -xpg4.2 .
.Sh HISTORY
The
.Fn usleep
function appeared in
.Bx 4.3 .
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