A bit late to the game but for the sake of completion...
Instead of 'waiting' for all tasks to finish, you can think in terms of the Hollywood principle, "don't call me, I'll call you" - when I'm finished.
I think the resulting code is more elegant...
Guava offers some interesting tools to accomplish this.
An example:
Wrap an ExecutorService into a ListeningExecutorService:
ListeningExecutorService service = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(10));
Submit a collection of callables for execution ::
for (Callable<Integer> callable : callables) {
ListenableFuture<Integer> lf = service.submit(callable);
// listenableFutures is a collection
listenableFutures.add(lf)
});
Now the essential part:
ListenableFuture<List<Integer>> lf = Futures.successfulAsList(listenableFutures);
Attach a callback to the ListenableFuture, that you can use to be notified when all futures complete:
Futures.addCallback(lf, new FutureCallback<List<Integer>> () {
@Override
public void onSuccess(List<Integer> result) {
// do something with all the results
}
@Override
public void onFailure(Throwable t) {
// log failure
}
});
This also offers the advantage that you can collect all the results in one place once the processing is finished...
More information here