Spring Parallel Execution Of A Method

Question

I am in the situation where I have a collection of objects and every object has to run an expensive method that takes about 5-10 seconds to complete.

How can I run all methods in parallel and check the status periodically?

I tried to use the @Async annotation with a Future response, but nothing changed.

public static void populate(String marketId) {
    //irrelevant code removed

    List<Company> companies = mongo().find(new Query(c), Company.class);
    List<Future> futures = new ArrayList<Future>();

    for(Company comp : companies) {
        futures.add(comp.updateData(market));
    }
}

@Async
public Future<Boolean> updateData(Market market) {
    //do my slow logic here

    return new AsyncResult(false);

}

Is the ThreadPoolTaskExecutor the way to go?

Answer 1

I'm a bit confused as to the reasons you use AsyncResult (and which implementation... ejb?). If I'm not mistaken, it will not work that way, as (from what I know) AsyncResult is connected to the bean and @Asyncronous annotation making the response from a specific bean method assyncronous. But if used inside an object, it would be effectively sequential.

What you need here is a normal Future. If so, you need to actually run these futures in an executor and than wait until they finish by calling future.get(). A nice tutorial on that you can find here: http://java.dzone.com/articles/javautilconcurrentfuture

You can also look into Akka. Actor model is my personal favourite, as you can simply spawn a bunch of workers, tell them what to do, and let them let you know once they're done with their job. Still it might be an overkill if you only have a simple task at hand, depends on your style.

ExecutorService pool = Executors.newFixedThreadPool(10);

public static void populate(String marketId) {
    //irrelevant code removed

    List<Company> companies = mongo().find(new Query(c), Company.class);
    List<Future> futures = new ArrayList<Future>();

    for(Company comp : companies) {
        futures.add(comp.updateData(market));
    }

    for(Future future: futures) {
        future.get()
    }
}

public Future<Boolean> updateData(Market market) {
  return pool.submit(new Callable<Boolean>() {
            @Override
            public Void call() throws Exception {
                //do your slow stuff here;
                return false;
            }
        })

}

of cause this makes sense if you need to get some actual return from those futures. If they're void, and you just need a thread to run some side-effects somewhere else, than there's no point in doing it that way, and you can simply use runnables and executor. Something similar to this: wait until all threads finish their work in java