private void notifyDataSubscribers() {
    final boolean isFailure = hasFailed();
    final boolean isCancellation = wasCancelled();
    for (Pair<DataSubscriber<T>, Executor> pair : mSubscribers) {
      notifyDataSubscriber(pair.first, pair.second, isFailure, isCancellation);
    }
  }
Subclasses should override this method to close the result that is not needed anymore.

<p>This method is called in two cases: 1. to clear the result when data source gets closed 2.
to clear the previous result when a new result is set
fbcore/src/main/java/com/facebook/datasource/AbstractDataSource.java