final String key = "key";

    final AtomicLongMap<String> map = AtomicLongMap.create();

    ExecutorService threadPool = Executors.newFixedThreadPool(nThreads);
    ArrayList<Future<Long>> futures = new ArrayList<>();
    for (int i = 0; i < nTasks; i++) {
      futures.add(
          threadPool.submit(
              new Callable<Long>() {
                @Override
                public Long call() {

    final String key = "key";

    final AtomicLongMap<String> map = AtomicLongMap.create();

    ExecutorService threadPool = Executors.newFixedThreadPool(nThreads);
    ArrayList<Future<Long>> futures = new ArrayList<>();
    for (int i = 0; i < nTasks; i++) {
      futures.add(
          threadPool.submit(
              new Callable<Long>() {
                @Override
                public Long call() {

        }
        throw new SearchEngineClientException("client is not HttpClient.");
    }

    //
    // Fesen Client
    //

    @Override
    public ThreadPool threadPool() {
        return client.threadPool();
    }

    @Override
    public AdminClient admin() {
        return client.admin();
    }

    @Override