my ($quit, $next_req, $cur_time, $cnt) = (0,0,0,0);
while (!$quit) {
   <<<do stuff>>>
   if ($cur_time<time) {
      # A new second has arrived, permit 3 more requests
      $cnt=3;
      $cur_time=time;
   }
   if ($cnt) {
      --$cnt;
      request(...);
   }
   <<<do more stuff>>>
}