// Test with listener1
        factory.setOnDestroyListener(listener1);
        assertEquals(listener1, factory.getOnDestroyListener());
        factory.destroyObject(pooledObject);
        assertEquals(1, events.size());
        assertEquals("listener1", events.get(0));

        // Switch to listener2
        factory.setOnDestroyListener(listener2);
        assertEquals(listener2, factory.getOnDestroyListener());

        };

        ShutdownListener listener2 = new ShutdownListener() {
            @Override
            public void onShutdown() {
                callCount.addAndGet(10);
            }
        };

        // Add first listener
        jobExecutor.addShutdownListener(listener1);
        assertEquals(listener1, jobExecutor.shutdownListener);

        // Replace with second listener

    queue.enqueue(incrementingEvent(counters, listener1, 1));
    queue.enqueue(incrementingEvent(counters, listener1, 2));

    Object listener2 = new Object();
    queue.addListener(listener2, directExecutor());
    queue.enqueue(incrementingEvent(counters, multiset(listener1, 3, listener2, 1)));
    queue.enqueue(incrementingEvent(counters, multiset(listener1, 4, listener2, 2)));
    assertEquals(0, counters.size());
    queue.dispatch();

    queue.enqueue(incrementingEvent(counters, listener1, 1));
    queue.enqueue(incrementingEvent(counters, listener1, 2));

    Object listener2 = new Object();
    queue.addListener(listener2, directExecutor());
    queue.enqueue(incrementingEvent(counters, multiset(listener1, 3, listener2, 1)));
    queue.enqueue(incrementingEvent(counters, multiset(listener1, 4, listener2, 2)));
    assertEquals(0, counters.size());
    queue.dispatch();

        // Add second listener (should replace first)
        TestShutdownListener listener2 = new TestShutdownListener();
        scriptExecutor.addShutdownListener(listener2);

        // Call shutdown
        scriptExecutor.shutdown();

        // Verify only second listener was called
        assertFalse(listener1.wasShutdownCalled());
        assertTrue(listener2.wasShutdownCalled());

import org.apache.maven.api.annotations.Experimental;
import org.apache.maven.api.annotations.Nonnull;

/**
 * A listener for session events.
 * TODO: open this to other events like similar to {@code org.apache.maven.eventspy.EventSpy}
 *
 * @since 4.0.0
 */
@Experimental
@FunctionalInterface
@Consumer
public interface Listener {
    void onEvent(@Nonnull Event event);

   * across calls to multiple listeners. Specifically, a given listener will have its callbacks
   * invoked in the same order as the underlying service enters those states. Additionally, at most
   * one of the listener's callbacks will execute at once. However, multiple listeners' callbacks
   * may execute concurrently, and listeners may execute in an order different from the one in which
   * they were registered.

    void enqueueStoppedEvent() {
      listeners.enqueue(STOPPED_EVENT);
    }

    void enqueueHealthyEvent() {
      listeners.enqueue(HEALTHY_EVENT);
    }

    void enqueueFailedEvent(Service service) {
      listeners.enqueue(
          new ListenerCallQueue.Event<Listener>() {
            @Override
            public void call(Listener listener) {
              listener.failure(service);
            }

   * across calls to multiple listeners. Specifically, a given listener will have its callbacks
   * invoked in the same order as the underlying service enters those states. Additionally, at most
   * one of the listener's callbacks will execute at once. However, multiple listeners' callbacks
   * may execute concurrently, and listeners may execute in an order different from the one in which
   * they were registered.

  final @Nullable Listener listeners() {
    return listeners;
  }

  final void releaseWaiters() {}

  AbstractFutureState() {}

  static final Object NULL = new Object();

  static final LazyLogger log = new LazyLogger(AbstractFuture.class);

  static final boolean GENERATE_CANCELLATION_CAUSES = false;

  private volatile @Nullable Object value;

  private volatile @Nullable Listener listeners;