Java: How to wake thread on demand?

Question

Let's say I want to create an object that basically runs a thread infinitely. I want the thread to sleep while there is no need for him, but when there is a need for certain job to be done, it wakes the thread - gets the job done and goes back to sleep. I also want the jobs to be queued and be executed in the order they arrive. In cocoa/objective c there is an NSOperationQueue for that. I wonder if java has something similar.

What do you think?

Answer 1

I would use an ExecutorService like

private final ExecutorService executor = Executors.newSingleThreadExecutor();

public void task(final int arg) {
    executor.execute(new Runnable() {
        @Override
        public void run() {
            // perform task using `arg`
        }
    });
}

This has a built in thread which wakes when a tasks is added and sleeps when there is no tasks left, a Blocking Queue for queue tasks.

Answer 2

I think a combination of a BlockingQueue and a ThreadPoolExecutor will do what you need.

Or, if you deploy on a Java EE app server, you could use JMS and a message-driven bean.