/** Queues with tasks that are currently executing their [TaskQueue.activeTask]. */
  private val busyQueues = mutableListOf<TaskQueue>()

  /** Queues not in [busyQueues] that have non-empty [TaskQueue.futureTasks]. */
  private val readyQueues = mutableListOf<TaskQueue>()

  private val runnable: Runnable =
    object : Runnable {
      override fun run() {
        var incrementedRunCallCount = false
        while (true) {

    final Runnable runChosenTest =
        new Runnable() {
          @Override
          public void run() {
            runChosenTest();
          }
        };
    final FutureTask<@Nullable Void> task = new FutureTask<>(runChosenTest, null);
    startThread(
        new Runnable() {
          @Override
          public void run() {
            task.run();
          }
        });

    final Runnable runChosenTest =
        new Runnable() {
          @Override
          public void run() {
            runChosenTest();
          }
        };
    final FutureTask<@Nullable Void> task = new FutureTask<>(runChosenTest, null);
    startThread(
        new Runnable() {
          @Override
          public void run() {
            task.run();
          }
        });

     * Any of the setException() calls below can fail if the output Future is cancelled between now
     * and then. This means that we're silently swallowing an exception -- maybe even an Error. But
     * this is no worse than what FutureTask does in that situation. Additionally, because the
     * Future was cancelled, its listeners have been run, so its consumers will not hang.
     *

         * Future might not even be a ListenableFuture, just a plain Future. That said, similar
         * problems can exist with methods like FutureTask.done(), not to mention slow calls to
         * Thread.interrupt() (as discussed in InterruptibleTask). At the end of the day, it's
         * unlikely that cancel() will be slow, so we can probably get away with calling it while