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.\"     @(#)usleep.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/gen/usleep.3,v 1.19 2007/01/09 00:27:56 imp Exp $
.\"
.Dd February 13, 1998
.Dt USLEEP 3
.Os
.Sh NAME
.Nm usleep
.Nd suspend thread execution for an interval measured in microseconds
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fo usleep
.Fa "useconds_t useconds"
.Fc
.Sh DESCRIPTION
The
.Fn usleep
function suspends execution of the calling thread until either
.Fa useconds
microseconds have elapsed
or a signal is delivered to the thread whose action
is to invoke a signal-catching function
or to terminate the thread or process.
The actual time slept may be longer, due to system latencies
and possible limitations in the timer resolution of the hardware.
.Pp
This function is implemented, using
.Xr nanosleep 2 ,
by pausing for
.Fa useconds
microseconds or until a signal occurs.
Consequently, in this implementation,
sleeping has no effect on the state of process timers
and there is no special handling for SIGALRM.
.Sh RETURN VALUES
.Rv -std usleep
.Sh ERRORS
The
.Fn usleep
function
will fail if:
.Bl -tag -width Er
.It Bq Er EINTR
A signal was delivered to the process and its
action was to invoke a signal-catching function.
.El
.Sh SEE ALSO
.Xr nanosleep 2 ,
.Xr sleep 3
.Sh HISTORY
The
.Fn usleep
function appeared in
.Bx 4.3 .