queue.enqueue(incrementingEvent(counters, listener, 3));
    queue.enqueue(incrementingEvent(counters, listener, 4));
    assertEquals(0, counters.size());
    queue.dispatch();
    assertEquals(multiset(listener, 4), counters);
  }

  public void testEnqueueAndDispatch_multipleListeners() {
    Object listener1 = new Object();
    ListenerCallQueue<Object> queue = new ListenerCallQueue<>();

      Queues.newConcurrentLinkedQueue();

  private Dispatcher dispatcher;

  public void testPerThreadQueuedDispatcher() {
    dispatcher = Dispatcher.perThreadDispatchQueue();
    dispatcher.dispatch(1, integerSubscribers.iterator());

    assertThat(dispatchedSubscribers)
        .containsExactly(
            i1,
            i2,
            i3, // Integer subscribers are dispatched to first.
            s1,

      Queues.newConcurrentLinkedQueue();

  private Dispatcher dispatcher;

  public void testPerThreadQueuedDispatcher() {
    dispatcher = Dispatcher.perThreadDispatchQueue();
    dispatcher.dispatch(1, integerSubscribers.iterator());

    assertThat(dispatchedSubscribers)
        .containsExactly(
            i1,
            i2,
            i3, // Integer subscribers are dispatched to first.
            s1,

/**
 * An {@link EventBus} that takes the Executor of your choice and uses it to dispatch events,
 * allowing dispatch to occur asynchronously.
 *
 * @author Cliff Biffle
 * @since 10.0
 */
@ElementTypesAreNonnullByDefault
public class AsyncEventBus extends EventBus {

  /**
   * Creates a new AsyncEventBus that will use {@code executor} to dispatch events. Assigns {@code
   * identifier} as the bus's name for logging purposes.
   *

  abstract void dispatch(Object event, Iterator<Subscriber> subscribers);

  /** Implementation of a {@link #perThreadDispatchQueue()} dispatcher. */
  private static final class PerThreadQueuedDispatcher extends Dispatcher {

    // This dispatcher matches the original dispatch behavior of EventBus.

    /** Per-thread queue of events to dispatch. */
    private final ThreadLocal<Queue<Event>> queue =

    queue.enqueue(incrementingEvent(counters, listener, 3));
    queue.enqueue(incrementingEvent(counters, listener, 4));
    assertEquals(0, counters.size());
    queue.dispatch();
    assertEquals(multiset(listener, 4), counters);
  }

  public void testEnqueueAndDispatch_multipleListeners() {
    Object listener1 = new Object();
    ListenerCallQueue<Object> queue = new ListenerCallQueue<>();

    // Now we find the task in our Executor and explicitly activate it.
    List<Runnable> tasks = executor.getTasks();
    assertEquals("One event dispatch task should be queued.", 1, tasks.size());

    tasks.get(0).run();

    assertEquals("One event should be delivered.", 1, events.size());
    assertEquals("Correct string should be delivered.", EVENT, events.get(0));

 * #enqueue enqueueing} and then {@linkplain #dispatch dispatching} events.
 *
 * <p>The API of this class is designed to make it easy to achieve the following properties
 *
 * <ul>
 *   <li>Multiple events for the same listener are never dispatched concurrently.
 *   <li>Events for the different listeners are dispatched concurrently.
 *   <li>All events for a given listener dispatch on the provided {@link #executor}.

        MoreExecutors.directExecutor(),
        Dispatcher.perThreadDispatchQueue(),
        exceptionHandler);
  }

  EventBus(
      String identifier,
      Executor executor,
      Dispatcher dispatcher,
      SubscriberExceptionHandler exceptionHandler) {
    this.identifier = checkNotNull(identifier);
    this.executor = checkNotNull(executor);
    this.dispatcher = checkNotNull(dispatcher);

   * #monitor}.
   */
  private void dispatchListenerEvents() {
    if (!monitor.isOccupiedByCurrentThread()) {
      listeners.dispatch();
    }
  }

  private void enqueueStartingEvent() {
    listeners.enqueue(STARTING_EVENT);
  }

  private void enqueueRunningEvent() {
    listeners.enqueue(RUNNING_EVENT);
  }