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

        this.pathToLease = new ConcurrentHashMap<>();
        this.fileCache = new ConcurrentHashMap<>();
        this.lock = new ReentrantReadWriteLock();

        // Start cleanup executor for expired leases
        this.cleanupExecutor = Executors.newSingleThreadScheduledExecutor(r -> {
            Thread t = new Thread(r, "LeaseManager-Cleanup");
            t.setDaemon(true);
            return t;
        });

        final int numThreads = 10;
        final ExecutorService executor = Executors.newFixedThreadPool(numThreads);
        final CountDownLatch latch = new CountDownLatch(numThreads);
        final AtomicInteger callbackCount = new AtomicInteger(0);

        // Add listeners concurrently from multiple threads
        for (int i = 0; i < numThreads; i++) {
            executor.submit(() -> {
                try {

        final ExecutorService executor = Executors.newFixedThreadPool(threadCount);
        final CountDownLatch startLatch = new CountDownLatch(1);
        final AtomicInteger errors = new AtomicInteger(0);

        final List<Future<?>> futures = new ArrayList<>();
        for (int t = 0; t < threadCount; t++) {
            final int threadId = t;
            futures.add(executor.submit(() -> {
                try {

  /**
   * Returns a snapshot of tasks currently scheduled for execution. Does not include the
   * currently-executing task unless it is also scheduled for future execution.
   */
  val scheduledTasks: List<Task>
    get() = taskRunner.withLock { futureTasks.toList() }

  /**
   * Schedules [task] for execution in [delayNanos]. A task may only have one future execution

    val boom = RuntimeException("boom!")
    addInterceptor(network) { chain: Interceptor.Chain? -> throw boom }
    val executor = ExceptionCatchingExecutor()
    client =
      client
        .newBuilder()
        .dispatcher(Dispatcher(executor))
        .build()
    val request =
      Request
        .Builder()
        .url(server.url("/"))
        .build()

    List<StringCatcher> catchers = new CopyOnWriteArrayList<>();
    List<Future<?>> futures = new ArrayList<>();
    ExecutorService executor = newFixedThreadPool(10);
    int numberOfCatchers = 10000;
    for (int i = 0; i < numberOfCatchers; i++) {
      futures.add(executor.submit(new Registrator(bus, catchers)));
    }
    for (int i = 0; i < numberOfCatchers; i++) {
      futures.get(i).get();
    }

    List<StringCatcher> catchers = new CopyOnWriteArrayList<>();
    List<Future<?>> futures = new ArrayList<>();
    ExecutorService executor = newFixedThreadPool(10);
    int numberOfCatchers = 10000;
    for (int i = 0; i < numberOfCatchers; i++) {
      futures.add(executor.submit(new Registrator(bus, catchers)));
    }
    for (int i = 0; i < numberOfCatchers; i++) {
      futures.get(i).get();
    }

 */
class TaskFaker : Closeable {
  val logger = Logger.getLogger("TaskFaker." + instance++)

  /** Though this executor service may hold many threads, they are not executed concurrently. */
  private val tasksExecutor = Executors.newCachedThreadPool(threadFactory("TaskFaker"))

  /**
   * True if this task faker has ever had multiple tasks scheduled to run concurrently. Guarded by
   * `this`.
   */
  var isParallel = false

java.util.concurrent.Executors#newFixedThreadPool(int)
java.util.concurrent.Executors#newSingleThreadExecutor()
java.util.concurrent.Executors#newCachedThreadPool()
java.util.concurrent.Executors#newSingleThreadScheduledExecutor()
java.util.concurrent.Executors#newScheduledThreadPool(int)
java.util.concurrent.Executors#defaultThreadFactory()