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.Dd November 4, 1997
.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 .