docs: def _queue_task(self, bucket, file_pair_list, transfer_config, subscribers, direction):
          ''' queue the upload/download - when get processed when resources available
              Use class level transfer_config if not defined. '''
          config = transfer_config if transfer_config else self._transfer_config
  
          _call_args = CallArgs(bucket=bucket,
                                file_pair_list=file_pair_list,
                                transfer_config=config,
                                subscribers=subscribers,
                                direction=direction,
                                transfer_spec=None,
                                transfer_spec_func=self._create_transfer_spec,
                                transfer_id=str(uuid.uuid4()))
  
          self._validate_args(_call_args)
          return self._coordinator_controller._queue_task(_call_args)