CountingRunnable listener = new CountingRunnable();

    future.addListener(listener, directExecutor());
    listener.assertNotRun();

    future.set(1);
    listener.assertRun();
  }

  public void testListenLaterFailed() {
    CountingRunnable listener = new CountingRunnable();

    future.addListener(listener, directExecutor());
    listener.assertNotRun();

    private final ArtifactTransferListener listener;

    private final Map<Resource, ArtifactTransferResource> artifacts;

    private final Map<Resource, Long> transfers;

    public static TransferListener newAdapter(ArtifactTransferListener listener) {
        if (listener == null) {
            return null;
        } else {
            return new TransferListenerAdapter(listener);
        }
    }

    Listener listener;
    synchronized (this) {
      listener = listeners.get(state);
    }

    if (code == null || listener == null) {
      return new MockResponse()
          .setResponseCode(404)
          .setBody("unexpected request");
    }

    try {
      OAuthSession session = slackApi.exchangeCode(code, redirectUrl());
      listener.sessionGranted(session);

     * asynchronous process to connect the socket. Once that succeeds or fails, `listener` will be
     * notified. The caller must cancel the returned event source when it is no longer in use.
     */
    fun newEventSource(
      request: Request,
      listener: EventSourceListener,
    ): EventSource
  }

    CountingRemovalListener<Object, Object> listener = countingRemovalListener();
    LoadingCache<Object, Object> nullCache =
        CacheBuilder.newBuilder().maximumSize(0).removalListener(listener).build(identityLoader());
    assertEquals(0, nullCache.size());
    Object key = new Object();
    assertSame(key, nullCache.getUnchecked(key));
    assertEquals(1, listener.getCount());
    assertEquals(0, nullCache.size());

![Events Diagram](../assets/images/******@****.***)

Here’s a [sample event listener](https://github.com/square/okhttp/blob/master/samples/guide/src/main/java/okhttp3/recipes/PrintEventsNonConcurrent.java) that prints each event with a timestamp.

```java
class PrintingEventListener extends EventListener {

public class PropertyDetailRenderer {
    private final GenerationListener listener;
    private final LinkRenderer linkRenderer;
    private final ElementWarningsRenderer warningsRenderer = new ElementWarningsRenderer();

    public PropertyDetailRenderer(LinkRenderer linkRenderer, GenerationListener listener) {
        this.linkRenderer = linkRenderer;
        this.listener = listener;
    }

   * executor}.
   *
   * @param listener the backing listener
   * @param executor the executor with which removal notifications are asynchronously executed
   */
  public static <K, V> RemovalListener<K, V> asynchronous(
      RemovalListener<K, V> listener, Executor executor) {
    checkNotNull(listener);
    checkNotNull(executor);
    return (RemovalNotification<K, V> notification) ->

            final ClassRealm realm,
            final ConfigurationListener listener)
            throws ComponentConfigurationException {
        try {
            ClassRealmConverter.pushContextRealm(realm);

            this.configureComponent(component, configuration, evaluator, (ClassLoader) realm, listener);
        } finally {
            ClassRealmConverter.popContextRealm();
        }
    }

	"istio.io/istio/pkg/network"
)

func SetupMonitoring(port int, path string, stop <-chan struct{}) {
	if port <= 0 {
		return
	}
	mux := http.NewServeMux()
	var listener net.Listener
	var err error
	if listener, err = net.Listen("tcp", fmt.Sprintf(":%d", port)); err != nil {
		log.Errorf("unable to listen on socket: %v", err)
		return
	}
	exporter, err := monitoring.RegisterPrometheusExporter(nil, nil)