for (int i = 0; i < size; i++) {
      builder.add(i);
    }
    keys = builder.build();
    threadPool =
        Executors.newFixedThreadPool(threads, new ThreadFactoryBuilder().setDaemon(true).build());
  }

  @Benchmark
  long add(final int reps) throws ExecutionException, InterruptedException {
    return doMultithreadedLoop(
        new Callable<Long>() {
          @Override