How can I call alarm() or usleep() from Perl?

    It's available as a built-in as of version 3.038.  If you want finer
    granularity than 1 second (as usleep() provides) and have itimers and
    syscall() on your system, you can use the following.  You could also
    use select().

    It takes a floating-point number representing how long to delay until
    you get the SIGALRM, and returns a floating- point number representing
    how much time was left in the old timer, if any.  Note that the C
    function uses integers, but this one doesn't mind fractional numbers.

    # alarm; send me a SIGALRM in this many seconds (fractions ok)
    # tom christiansen <tchrist@convex.com>
    sub alarm {
        require 'syscall.ph';
        require 'sys/time.ph';

        local($ticks) = @_;
        local($in_timer,$out_timer);
        local($isecs, $iusecs, $secs, $usecs);

        local($itimer_t) = 'L4'; # should be &itimer'typedef()

        $secs = int($ticks);
        $usecs = ($ticks - $secs) * 1e6;

        $out_timer = pack($itimer_t,0,0,0,0);  
        $in_timer  = pack($itimer_t,0,0,$secs,$usecs);

        syscall(&SYS_setitimer, &ITIMER_REAL, $in_timer, $out_timer)
            && die "alarm: setitimer syscall failed: $!";

        ($isecs, $iusecs, $secs, $usecs) = unpack($itimer_t,$out_timer);
        return $secs + ($usecs/1e6);
    }