sub do_request {
    use Time::HiRes qw[sleep time];
    use 5.010;
    state $sleep = [0, 0, 0];
    my $url = shift;
    while ($$sleep[0] + 1 > time) {
        # Loop, as sleep() may get interrupted.
        sleep time - $$sleep[0] + 1;
    }
    $sleep = [@$sleep [1 .. $#$sleep], time];
    ... fetch from server ...
}