override fun start() {
      taskRunner.assertLockHeld()
      require(currentTask == this)
      activeThreads++

      tasksExecutor.execute {
        taskRunner.assertLockNotHeld()
        require(currentTask == this)
        try {
          runnable.run()
          require(currentTask == this) { "unexpected current task: $currentTask" }
        } finally {
          taskRunner.withLock {

  }

  public void testToString() {
    Runnable[] currentTask = new Runnable[1];
    Executor delegate =
        new Executor() {
          @Override
          public void execute(Runnable task) {
            currentTask[0] = task;
            task.run();
            currentTask[0] = null;
          }

          @Override
          public String toString() {