Executing code in parallel in Java

Question

I have this very basic script which performs a Redis server request but I do not understand multithreading enough as to successfully make it run in parallel. This is what I have in my main() method

        Jedis jedis1 = new Jedis("10.10.25.54", 6381);
        Jedis jedis2 = new Jedis("10.10.25.54", 6382);
        Jedis jedis3 = new Jedis("10.10.25.54", 6383);
        Jedis jedis4 = new Jedis("10.10.25.54", 6384);
        Jedis jedis5 = new Jedis("10.10.25.54", 6385);
        Jedis jedis6 = new Jedis("10.10.25.54", 6386);
        Jedis jedis7 = new Jedis("10.10.25.54", 6387);
        Jedis jedis8 = new Jedis("10.10.25.54", 6388);

        // The bit i would like to learn how run in parallel
        //
        System.out.println(jedis1.eval(SCRIPT, 0).toString());
        System.out.println(jedis2.eval(SCRIPT, 0).toString());
        System.out.println(jedis3.eval(SCRIPT, 0).toString());
        System.out.println(jedis4.eval(SCRIPT, 0).toString());
        System.out.println(jedis5.eval(SCRIPT, 0).toString());
        System.out.println(jedis6.eval(SCRIPT, 0).toString());
        System.out.println(jedis7.eval(SCRIPT, 0).toString());
        System.out.println(jedis8.eval(SCRIPT, 0).toString());

Answer 1

Multithreadding and concurrency is a fairly large topic in Java, too big to answer in a single question, and there any many possible solutions. However I recommend reading the Orical Concurrency tutorials .

My approach would be:

ExecutorService es = Executors.newCachedThreadPool();

es.submit(new RunJedis(jedis1));
es.submit(new RunJedis(jedis2));
es.submit(new RunJedis(jedis3));
es.submit(new RunJedis(jedis4));
es.submit(new RunJedis(jedis5));
es.submit(new RunJedis(jedis6));
es.submit(new RunJedis(jedis7));
es.submit(new RunJedis(jedis8));

class RunJedis{
    Jedis jedis;
    RunJedis(Jedis jedis1){
        this.jedis=jedis1;
    }

    void run(){ 
        System.out.println(jedis.eval(SCRIPT, 0).toString());
    }
}

However, this wouldn't be guaranteed to use multiple threads. You are leaving it up to the executor service to decide how is best.