/** Use {@link MoreExecutors#newSequentialExecutor} */
  SequentialExecutor(Executor executor) {
    this.executor = Preconditions.checkNotNull(executor);
  }

  /**
   * Adds a task to the queue and makes sure a worker thread is running.
   *
   * <p>If this method throws, e.g. a {@code RejectedExecutionException} from the delegate executor,
   * execution of tasks will stop until a call to this method is made.
   */

      final Runnable runnable;
      final Executor executor;

      RunnableExecutorPair(Runnable runnable, Executor executor) {
        this.runnable = runnable;
        this.executor = executor;
      }

      void execute() {
        try {
          executor.execute(runnable);
        } catch (RuntimeException e) {
          log.log(
              Level.SEVERE,

  }

  /**
   * Adds a listener that will be called using the given executor when events are later {@link
   * #enqueue enqueued} and {@link #dispatch dispatched}.
   */
  public void addListener(L listener, Executor executor) {
    checkNotNull(listener, "listener");
    checkNotNull(executor, "executor");
    listeners.add(new PerListenerQueue<>(listener, executor));
  }

  /**

    addEdge(5, 6, "baz");

    int threadCount = 20;
    ExecutorService executor = newFixedThreadPool(threadCount);
    final CyclicBarrier barrier = new CyclicBarrier(threadCount);
    ImmutableList.Builder<Future<?>> futures = ImmutableList.builder();
    for (int i = 0; i < threadCount; i++) {
      futures.add(
          executor.submit(
              new Callable<@Nullable Void>() {
                @Override

  }

  public void testNoOpScheduledExecutorShutdown() {
    ListeningScheduledExecutorService executor = TestingExecutors.noOpScheduledExecutor();
    assertFalse(executor.isShutdown());
    assertFalse(executor.isTerminated());
    executor.shutdown();
    assertTrue(executor.isShutdown());
    assertTrue(executor.isTerminated());
  }

   */
  public <T extends @Nullable Object> ListenableFuture<T> submitAsync(
      AsyncCallable<T> callable, Executor executor) {
    checkNotNull(callable);
    checkNotNull(executor);
    TaskNonReentrantExecutor taskExecutor = new TaskNonReentrantExecutor(executor, this);
    AsyncCallable<T> task =
        new AsyncCallable<T>() {
          @Override

   *
   * @param listener the listener to run when the computation is complete
   * @param executor the executor to run the listener in
   * @throws RejectedExecutionException if we tried to execute the listener immediately but the
   *     executor rejected it.
   */
  void addListener(Runnable listener, Executor executor);

   *
   * @param listener the listener to run when the computation is complete
   * @param executor the executor to run the listener in
   * @throws RejectedExecutionException if we tried to execute the listener immediately but the
   *     executor rejected it.
   */
  void addListener(Runnable listener, Executor executor);

   *
   * @param listener the listener to run when the computation is complete
   * @param executor the executor to run the listener in
   * @throws RejectedExecutionException if we tried to execute the listener immediately but the
   *     executor rejected it.
   */
  void addListener(Runnable listener, Executor executor);

    executor.execute(task);
    return task;
  }

  /**
   * Executes {@code runnable} on the specified {@code executor}, returning a {@code Future} that
   * will complete after execution.
   *
   * @throws RejectedExecutionException if the task cannot be scheduled for execution
   * @since 28.2
   */
  public static ListenableFuture<@Nullable Void> submit(Runnable runnable, Executor executor) {