import java.util.Collections;
import java.util.List;
import java.util.Queue;
import java.util.concurrent.Executor;
import java.util.logging.Level;

/**
 * A list of listeners for implementing a concurrency friendly observable object.
 *
 * <p>Listeners are registered once via {@link #addListener} and then may be invoked by {@linkplain
 * #enqueue enqueueing} and then {@linkplain #dispatch dispatching} events.
 *