.\" Copyright (c) 1986, 1991 Regents of the University of California.
.\" All rights reserved.
.\"
.\" %sccs.include.redist.man%
.\"
.\"     @(#)usleep.3	6.4 (Berkeley) 04/19/91
.\"
.Dd 
.Dt USLEEP 3
.Os BSD 4.3
.Sh NAME
.Nm usleep
.Nd suspend execution for interval of microseconds
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft void
.Fn usleep "u_int microseconds"
.Sh DESCRIPTION
The
.Fn sleep
function
suspends execution of the calling process
for
.Fa microseconds
of time.
System activity or time spent in processing the
call may lengthen the sleep slightly.
.Pp
If a timer is already running on the process its state is saved.
If the value
.Fa microseconds
is more than or equal to the remaining clock time for the saved timer,
the sleep time is set to
the remaining clock time.
The state of the previous timer
is restored after
.Fa microseconds
has passed.
.Pp
This routine is implemented using 
.Xr setitimer 2 ;
it requires eight system calls 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, but would not interfere
with other uses of
.Xr setitimer .
.Sh SEE ALSO
.Xr setitimer 2 ,
.Xr getitimer 2 ,
.Xr sigpause 2 ,
.Xr ualarm 3 ,
.Xr sleep 3 ,
.Xr alarm 3
.Sh HISTORY
The
.Fn usleep
function appeared in 
.Bx 4.3 .