How do I create a ThreadPoolExecutor, create threads as needed and expire them when applicable?

My use case:

>Set the minimum size "n" for the thread pool, which means that "n" threads are always available after the executor starts. > Set the maximum size "m" for the thread pool. > When all "m" threads are busy, incoming tasks should be queued. > Expire (M - n) threads based on idle timeout

I believe the pool manager behind httpclient can make similar settings I'm trying to implement it using ThreadPoolExecutor, but I can't find a way Is it possible?

This is an example of a test

public class ExecutorExample {

    public static void main(String[] args) throws InterruptedException {
        int minPoolSize = 2;
        int maxPoolSize = 10;
        int ttlMillis = 100;
        ThreadPoolExecutor startupExecutor = new ThreadPoolExecutor(minPoolSize,maxPoolSize,// surprisingly this is not obeyed.
                ttlMillis,TimeUnit.MILLISECONDS,new LinkedBlockingQueue<Runnable>());

        for (int i = 0; i < 20; i++) {
            System.out.println(Thread.currentThread().getName() + ":" + startupExecutor.getCorePoolSize());
            startupExecutor.execute(new MyRunnable(i));
        }

        for (int i = 0; i < 20; i++) {
            Thread.sleep(1000);
            System.out.println(Thread.currentThread().getName() + ":" + startupExecutor.getCorePoolSize());
        }
    }

}

class MyRunnable implements Runnable {

    int n;

    public MyRunnable(int n) {
        this.n = n;
    }

    @Override
    public void run() {
        try {
            Thread.sleep(2000);
            System.out.println(Thread.currentThread().getName() + ":" + n);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }

}

Solution

How's this?

ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize,maximumPoolSize,keepAliveTime,unit,workQueue);

ThreadPoolExecutor

Edit: the queue I usually use is bounded blocking queue

BlockingQueue<Runnable> workQueue = new ArrayBlockingQueue(queueCapacity,true);

Edit2: the maximum pool size starts only when the queue is full Because you are using unbounded queues, the number of threads will not be higher than 2 The se link is as follows

rules-of-a-threadpoolexecutor-pool-size

Zoom in size 1 and you'll see the difference

new LinkedBlockingQueue<>(1));

Edit 3: in your example, use startupexecution Getpoolsize() change startupexecution getCorePoolSize().