private final StringSubscriber s2 = new StringSubscriber("s2");
  private final ImmutableList<Subscriber> stringSubscribers =
      ImmutableList.of(
          subscriber(bus, s1, "handleString", String.class),
          subscriber(bus, s2, "handleString", String.class));

  private final ConcurrentLinkedQueue<Object> dispatchedSubscribers = new ConcurrentLinkedQueue<>();

  private Dispatcher dispatcher;