break;
      case TERMINATED:
      case FAILED:
        throw new AssertionError();
    }
  }

  private void enqueueFailedEvent(final State from, final Throwable cause) {
    // can't memoize this one due to the exception
    listeners.enqueue(
        new ListenerCallQueue.Event<Listener>() {
          @Override
          public void call(Listener listener) {
            listener.failed(from, cause);