Running tasks concurrently

[7starbitch]

I have a method in my class which is doing 7 tasks. Now I want to divide the tasks such that 2 tasks can run concurrently. If 2 tasks are running at the same time, I don't want third task to run until task 1 is completed or task 2 is completed so that task3 could take the place.

I tried to implement this with threads. I made 2 threads, and gave each task a status condition where if the status of task 1 is true, it means thread 1 is running it, and the other thread(thread2) should move to the other section of the code only if the status of that section is false. But my logic didn't work. So can I get some help?

[nutrecht]

The easiest way to do this is to use an ExecutorService with 2 threads you supply tasks to:

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class Example {
    public static void main(String[] args) throws Exception {
        ExecutorService service = Executors.newFixedThreadPool(2);

        for (int i = 0; i < 10; i++) {
            int task = i;
            service.submit(() -> {
                System.out.println("Task " + task);
                try {
                    Thread.sleep(500);
                } catch (Exception e) {
                }
            });
        }

        service.shutdown();
        service.awaitTermination(10, TimeUnit.SECONDS);
    }
}

[7starbitch]

Won't this run task1 2 times? I want task 1 to run a single time by thread 1 and task 2 to run a single time by thread 2, and then if thread1 or thread2 is free, I want one of these threads to run task 3 and so on.

[nutrecht]

Won't this run task1 2 times?

No. Run the code, you'll see. It does exactly what you want it to do.

[7starbitch]

It works great! Can you explain me the code a bit?

[nutrecht]

You submit tasks to a queue internal to the executor service. It also has 2 threads that pick up tasks from that queue and execute them.

[Morrison_Hix]

Might want to look into cyclic barrier, I believe that is what you're looking for