Question

Problem Statement is:-

Each thread uses unique ID between 1 and 1000 and program has to run for 60 minutes or more, So in that 60 minutes it is possible that all the ID’s will get finished so I need to reuse those ID’s again,

I know several ways to do it, one way is the below that I wrote by taking help from StackOverflow, but when I tried running this, what I found is that, after few minutes of run this program gets very slow and it takes lot of time to print the ID on the console. And also I get OutOfMemory Error sometimes. Is there any better way to solve this kind of problem?

class IdPool {
    private final LinkedList<Integer> availableExistingIds = new LinkedList<Integer>();

    public IdPool() {
        for (int i = 1; i <= 1000; i++) {
            availableExistingIds.add(i);
        }
    }

    public synchronized Integer getExistingId() {
        return availableExistingIds.removeFirst();
    }

    public synchronized void releaseExistingId(Integer id) {
        availableExistingIds.add(id);
    }
}


class ThreadNewTask implements Runnable {
    private IdPool idPool;

    public ThreadNewTask(IdPool idPool) {
        this.idPool = idPool;
    }

    public void run() {
        Integer id = idPool.getExistingId();
        someMethod(id);
        idPool.releaseExistingId(id);
    }

    private void someMethod(Integer id) {
        System.out.println("Task: " +id);
    }
}

public class TestingPool {
    public static void main(String[] args) throws InterruptedException {
        int size = 10;
        int durationOfRun = 60;
        IdPool idPool = new IdPool();   
        // create thread pool with given size
        // create thread pool with given size
    ExecutorService service = new ThreadPoolExecutor(size, size, 500L, TimeUnit.MILLISECONDS, new ArrayBlockingQueue<Runnable>(10), new ThreadPoolExecutor.CallerRunsPolicy()); 


        // queue some tasks
        long startTime = System.currentTimeMillis();
        long endTime = startTime + (durationOfRun * 60 * 1000L);

        // Running it for 60 minutes
        while(System.currentTimeMillis() <= endTime) {
            service.submit(new ThreadNewTask(idPool));
        }

        // wait for termination        
        service.shutdown();
        service.awaitTermination(Long.MAX_VALUE, TimeUnit.DAYS); 
    }
}

Answer 1

I already explained you in your previous question that your code submitted millions and millions of tasks to the executor, since it submits tasks in a loop during 60 minutes, withot waiting.

It’s very unclear what your end goal is, but as is, you’re filling a queue of tasks until you don’t have any memory available anymore. Since you don’t explain the goal of your program, it’s hard to give you any solution.

But the first thing you could do is to limit the size of the task queue of your executor. This would force the main thread to block each time the queue is full.