for (int i = 0; i < numTasks; i++) {
            tasks.add(testCallable);
        }

        // 時間取得
        final long time = System.nanoTime();

        // Callableタスク(複数)を実行する
        final ExecutorService executor = Executors.newFixedThreadPool(numTasks);
        try {
            final List<Future<Integer>> futures = executor.invokeAll(tasks);