public static double dataRaceHypotenuse(double a, double b) {
    Lock lock = new ReentrantLock();
    double[] sum = {0.0};
    Future<Void> future = void_fork(() -> {
        lock.lock();
        try {
            sum[0] += a * a;
        } finally {
            lock.unlock();
        }
    });
    sum[0] += b * b;
    join(future);
    return Math.sqrt(sum[0]);
} 
public static double dataRaceFreeHypotenuse(double a, double b)