public Map<Aggregator, AggregatorData> roll(long newDataWindowEndTimeMillis) {
    Utils.checkState(started, "Not started");
    Utils.checkState(!stopped, "Already stopped");
    return dataProvider.roll(newDataWindowEndTimeMillis);
  }
public Map < Aggregator , AggregatorData > roll ( long newDataWindowEndTimeMillis ) { Utils . checkState ( started , "Not started" ) ; Utils . checkState ( ! stopped , "Already stopped" ) ; return dataProvider . roll ( newDataWindowEndTimeMillis ) ; }
Atomically rolls the DataWindow of all aggregators associated with the Aggregators instance.

@param newDataWindowEndTimeMillis ending time of the new DataWindow.
@return a Map with all the aggregators data of the DataWindow that closed.