code: def _get_countdown_for_next_slice(self, spec):
      
      countdown = 0
      if self._processing_limit(spec) != -1:
        countdown = max(
            int(parameters.config._SLICE_DURATION_SEC -
                (self._time() - self._start_time)), 0)
      return countdown
docs: Get countdown for next slice's task.
  
      When user sets processing rate, we set countdown to delay task execution.
  
      Args:
        spec: model.MapreduceSpec
  
      Returns:
        countdown in int.