- When `SchedulerQueueingHint` is enabled,
  the scheduler's in-tree plugins now subscribe to specific node events to decide whether to requeue Pods.
  This allows the scheduler to handle cluster events faster with less memory.

  Specific node events include updates to taints, tolerations or allocatable.

      private final Object event;
      private final Subscriber subscriber;

      private EventWithSubscriber(Object event, Subscriber subscriber) {
        this.event = event;
        this.subscriber = subscriber;
      }
    }
  }

  /** Implementation of {@link #immediate()}. */
  private static final class ImmediateDispatcher extends Dispatcher {

  private @Nullable H subscriber;

  H getSubscriber() {
    return subscriber;
  }

  @Override
  protected void setUp() throws Exception {
    subscriber = createSubscriber();
    EventBus bus = new EventBus();
    bus.register(subscriber);
    bus.post(EVENT);
  }

  @Override
  protected void tearDown() throws Exception {
    subscriber = null;
  }

import com.google.common.base.MoreObjects;

/**
 * Wraps an event that was posted, but which had no subscribers and thus could not be delivered.
 *
 * <p>Registering a DeadEvent subscriber is useful for debugging or logging, as it can detect
 * misconfigurations in a system's event distribution.
 *
 * @author Cliff Biffle
 * @since 10.0
 */
public class DeadEvent {

  private final Object source;