Collecting Return Values from Launched Threads? [latest Java]

Question

I'm looking for the simplest, most straightforward way to implement the following:

• main starts and launches 3 threads
• all 3 tasks process and end in a resulting value (which I need to return somehow?)
• main waits (.join?) on each thread to ensure they have all 3 completed their task
• main somehow gets the value from each thread (3 values)

Then the rest is fairly simple, processes the 3 results and then terminates...

Now, I've been doing some reading and found multiple ideas, like:

• Using Future, but this is for asynch, is this really a good idea when the main thread needs to block waiting for all 3 spawned threads to finsih?
• Passing in an object (to a thread) and then simply having the thread "fill it" with the result
• Somehow using Runnable (not sure how yet).

Anyways - what would be the best, and simplest recommended approach? Thanks,

Answer 1

List<Callable<Result>> list = ... create list of callables

ExecutorService es = Executors.newFixedThreadPool(3);
List<Future<Result>> results = es.invokeAll(list);

ExecutorService.invokeAll method will return only after all tasks (instances of Callable) finished, either normally or by throwing exception.

For details see ExecutorService (mainly its invokeAll method), Executors, Callable.