code: def _on_timeout():
      
      global _buffer_size
  
      LOGGER.debug('No metrics submitted in the last %.2f seconds',
                   _timeout_interval / 1000.0)
      _buffer_size = _pending_measurements()
      if _buffer_size:
          return _trigger_batch_write()
      _start_timeout()
docs: Invoked periodically to ensure that metrics that have been collected
      are submitted to InfluxDB.
  
      :rtype: tornado.concurrent.Future or None