code: public void pingLoop() {
          if ( ! isStopped() ) {
              Log.Info(this, "----------- START MULTI RESPONSE REQUEST ------------");
              mediator.askSubscribers(self(), "defaultTopic", "Hello from " + myName,
                  (reply, error) -> {
                      if (Actors.isComplete(error)) {
                          Log.Info(this,"----------- ALL RESULTS RECEIVED ------------");
                          delayed(5000, () -> pingLoop());
                      } else {
                          Log.Info(this,"=>" + reply);
                      }
                  });
          }
      }
docs: instead of broadcasting fire-and-forget (tellMsg), this one send a request
  and receives results from each actor.