basic-lib/src/main/java/com/streamsets/pipeline/stage/processor/aggregation/aggregator/Aggregators.java
public void start(long newDataWindowEndTimeMillis) {
    Utils.checkState(!started, "Already started");
    Utils.checkState(!stopped, "Already stopped");
    dataProvider.start(newDataWindowEndTimeMillis);
    started = true;
  }
public void start(long newDataWindowEndTimeMillis) {
    Utils.checkState(!started, "Already started");
    Utils.checkState(!stopped, "Already stopped");
    dataProvider.start(newDataWindowEndTimeMillis);
    started = true;
  }
Starts the Aggregators instance.

@param newDataWindowEndTimeMillis ending time of the new DataWindow.