};
    addCallback(f, callback, directExecutor());
  }

  private class CountingSameThreadExecutor implements Executor {
    int runCount = 0;

    @Override
    public void execute(Runnable command) {
      command.run();
      runCount++;
    }
  }

  private final class MockCallback implements FutureCallback<String> {
    @Nullable private String value = null;

   * this method to use a custom {@link Executor}, which may configure its worker thread with a
   * specific name, thread group or priority. The returned executor's {@link
   * Executor#execute(Runnable) execute()} method is called when this service is started, and should
   * return promptly.
   *
   * <p>The default implementation returns a new {@link Executor} that sets the name of its threads

    }

    @SuppressWarnings("ThreadPriorityCheck") // TODO: b/175898629 - Consider onSpinWait.
    Interruptenator(Thread interruptee, AtomicBoolean shutdown) {
      super(
          new Runnable() {
            @Override
            public void run() {
              while (!shutdown.get()) {
                interruptee.interrupt();
                Thread.yield();
              }
            }

            Thread webFsCrawlerThread = null;
            Thread dataCrawlerThread = null;

            if (runAll || webConfigIdList != null || fileConfigIdList != null) {
                webFsCrawlerThread = new Thread((Runnable) () -> {
                    // crawl web
                    writeTimeToSessionInfo(crawlingInfoHelper, Constants.WEB_FS_CRAWLER_START_TIME);

    /** An array of supported language codes. */
    protected String[] supportedLanguages;

    /** A list of shutdown hooks to be executed on system shutdown. */
    protected List<Runnable> shutdownHookList = new ArrayList<>();

    /** The previous state of the cluster. */
    protected AtomicInteger previousClusterState = new AtomicInteger(0);

    /** The version of the Fess application. */

#### Do-stuff-later pool

Sometimes there's an action required like calling the application layer or responding to a ping, and the thread discovering the action is not the thread that should do the work. We enqueue a runnable on this executor and it gets handled by one of the executor's threads.

### Locks

We have 3 different things that we synchronize on.

#### Http2Connection

@SuppressWarnings("ShortCircuitBoolean")
abstract class AbstractTransformFuture<
        I extends @Nullable Object, O extends @Nullable Object, F, T extends @Nullable Object>
    extends FluentFuture.TrustedFuture<O> implements Runnable {
  static <I extends @Nullable Object, O extends @Nullable Object> ListenableFuture<O> createAsync(
      ListenableFuture<I> input,
      AsyncFunction<? super I, ? extends O> function,
      Executor executor) {

  }

  @SuppressWarnings("Java8ApiChecker")
  static class MyServerExampleWithCleaner implements AutoCloseable {
    private static final Cleaner cleaner = Cleaner.create();

    private static Runnable closeServerSocketRunnable(
        ServerSocket serverSocket, AtomicBoolean cleanerRan) {
      return () -> {
        try {
          serverSocket.close();
          cleanerRan.set(true);

  }

  @SuppressWarnings("Java8ApiChecker")
  static class MyServerExampleWithCleaner implements AutoCloseable {
    private static final Cleaner cleaner = Cleaner.create();

    private static Runnable closeServerSocketRunnable(
        ServerSocket serverSocket, AtomicBoolean cleanerRan) {
      return () -> {
        try {
          serverSocket.close();
          cleanerRan.set(true);

    assertTrue(ArbitraryInstances.get(ConcurrentMap.class).isEmpty());
    assertTrue(ArbitraryInstances.get(ConcurrentNavigableMap.class).isEmpty());
    ArbitraryInstances.get(Executor.class).execute(ArbitraryInstances.get(Runnable.class));
    assertNotNull(ArbitraryInstances.get(ThreadFactory.class));
    assertFreshInstanceReturned(
        BlockingQueue.class,
        BlockingDeque.class,
        PriorityBlockingQueue.class,