code: def _handle_processor_error(self, failure):
          
          # Check if we're stopping/stopped and the errback of the processor
          # deferred is just the cancelling we initiated.  If so, we skip
          # notifying via the _start_d deferred, as it will be 'callback'd at the
          # end of stop()
          if not (self._stopping and failure.check(CancelledError)):
              if self._start_d:  # Make sure we're not already stopped
                  self._start_d.errback(failure)
docs: Handle a failure in the processing of a block of messages
  
          This method is called when the processor func fails while processing
          a block of messages. Since we can't know how best to handle a
          processor failure, we just :func:`errback` our :func:`start` method's
          deferred to let our user know about the failure.