Question

I want a Thread-Pool that provides a maximum of X Threads to process tasks, so far no problem. However each submitted Task can specify an IO-Target which is specifically limited (say Y).

So a submitted IOTask returns the target “google.com” with limit 4 (Y) and the pool has a global limit 16 (X). I want to submit 10 google.com-tasks where only 4 are processed in parallel and the pool has 12 threads free for other tasks.

How can I achieve this?

Answer 1

You can wrap two ExecutorService instances in a custom class and manually manage the submission of tasks as follows:

class ExecutorWrapper {

    private ExecutorService ioExec = Executors.newFixedThreadPool(4);
    private ExecutorService genExec = Executors.newFixedThreadPool(12);

    public Future<?> submit(final IOTask task) {
        return ioExec.submit(task);
    }

    public Future<?> submit(final Runnable task) {
        return genExec.submit(task);
    }
}

interface IOTask extends Runnable {}

This allows you to use 4 threads to do the IO operations and leaves the other 12 threads to service the other tasks.