/** {@inheritDoc} */
 @Override
 public void onCompleted() {
   try {
     completionMarkerFound.set(true);
     resultQueue.put(ResultQueueEntry.<Row>completionMarker());
   } catch (InterruptedException e) {
     Thread.currentThread().interrupt();
     throw new RuntimeException("Interrupted while adding a ResultQueueEntry", e);
   }
 }