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

  /** Releases all threads in the {@link #waitersField} list, and clears the list. */
  final void releaseWaiters() {
    Waiter head = gasWaiters(Waiter.TOMBSTONE);
    for (Waiter currentWaiter = head; currentWaiter != null; currentWaiter = currentWaiter.next) {
      currentWaiter.unpark();
    }
  }

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

  /** Releases all threads in the {@link #waitersField} list, and clears the list. */
  final void releaseWaiters() {
    Waiter head = gasWaiters(Waiter.TOMBSTONE);
    for (Waiter currentWaiter = head; currentWaiter != null; currentWaiter = currentWaiter.next) {
      currentWaiter.unpark();
    }
  }