*/
  final boolean casListeners(@Nullable Listener expect, Listener update) {
    return ATOMIC_HELPER.casListeners(this, expect, update);
  }

  /**
   * Performs a {@linkplain java.lang.invoke.VarHandle#getAndSet get-and-set} operation on {@link
   * #listenersField}.
   */
  final @Nullable Listener gasListeners(Listener update) {
    return ATOMIC_HELPER.gasListeners(this, update);
  }

  /**

   */
  final boolean casListeners(@Nullable Listener expect, Listener update) {
    return ATOMIC_HELPER.casListeners(this, expect, update);
  }

  /**
   * Performs a {@linkplain java.lang.invoke.VarHandle#getAndSet get-and-set} operation on {@link
   * #listenersField}.
   */
  final @Nullable Listener gasListeners(Listener update) {
    return ATOMIC_HELPER.gasListeners(this, update);
  }

  /**

    private final ExecutionList executionList = new ExecutionList();

    // This allows us to only start up a thread waiting on the delegate future when the first
    // listener is added.
    private final AtomicBoolean hasListeners = new AtomicBoolean(false);

    // The delegate future.
    private final Future<V> delegate;

    ListenableFutureAdapter(Future<V> delegate) {
      this(delegate, defaultAdapterExecutor);
    }