code: def service_timeouts(self):
          
          queue = self._queue
          if self._new_timers:
              new_timers = self._new_timers
              while new_timers:
                  heappush(queue, new_timers.pop())
  
          if queue:
              now = time.time()
              while queue:
                  try:
                      timer = queue[0][1]
                      if timer.finish(now):
                          heappop(queue)
                      else:
                          return timer.end
                  except Exception:
                      log.exception("Exception while servicing timeout callback: ")
docs: run callbacks on all expired timers
          Called from the event thread
          :return: next end time, or None