code: def send(self):
          if not self._receive_has_been_called:
              all_addrs = self._dest_addrs
          else:
              all_addrs = [a for (i, a) in list(self._id_to_addr.items())
                           if i in self._remaining_ids]
          if self._last_used_id is None:
              self._last_used_id = int(time.time()) & 0xffff
          for addr in all_addrs:
              self._last_used_id = (self._last_used_id + 1) & 0xffff
              self._id_to_addr[self._last_used_id] = addr
              self._send_ping(addr, payload=struct.pack("d", time.time()))