<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_countdown_for_next_slice(self, spec):
 """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. """

    countdown = 0
    if self._processing_limit(spec) != -1:
      countdown = max(
          int(parameters.config._SLICE_DURATION_SEC -
              (self._time() - self._start_time)), 0)
    return countdown