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.\"     @(#)usleep.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD$
.\"
.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
.Fn usleep "useconds_t microseconds"
.Sh DESCRIPTION
The
.Fn usleep
function suspends execution of the calling thread until either
.Fa microseconds
microseconds have elapsed or a signal is delivered to the thread and its
action is to invoke a signal-catching function or to terminate the
process.
System activity or limitations may lengthen the sleep by an indeterminate amount.
.Pp
This function is implemented using
.Xr nanosleep 2
by pausing for
.Fa microseconds
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.
Also, this implementation does not put a limit on the value of
.Fa microseconds
(other than that limited by the size of the
.Ft useconds_t
type); some other platforms require it to be less than one million.
.Sh NOTE
The
.Fn usleep
function is obsolescent.
Use
.Xr nanosleep 2
instead.
.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 .