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.Dd $Mdocdate: October 16 2012 $
.Dt USLEEP 3
.Os
.Sh NAME
.Nm usleep
.Nd suspend process execution for interval measured in microseconds
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn usleep "useconds_t microseconds"
.Sh DESCRIPTION
.Bf -symbolic
This interface is obsoleted by
.Xr nanosleep 2 .
.Ef
.Pp
The
.Fn usleep
function suspends execution of the calling process until either
.Fa microseconds
microseconds have elapsed or a signal is delivered to the process and its
action is to invoke a signal-catching function or to terminate the
process.
The suspension time may be longer than requested due to the
scheduling of other activity by the system.
.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
.Dv 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 NOTES
A microsecond is 0.000001 seconds.
.Sh SEE ALSO
.Xr sleep 1 ,
.Xr nanosleep 2 ,
.Xr sleep 3
.Sh STANDARDS
The
.Fn usleep
function conforms to
.St -xpg4.2 .
.Sh HISTORY
The
.Fn usleep
function appeared in
.Bx 4.3 .
.Sh CAVEATS
Some implementations of
.Fn usleep
return an error if
.Fa microseconds
is greater than or equal to 1,000,000.
Portable applications should be written with this limitation in mind.