Clean way in GWT/Java to wait for multiple asynchronous events to finish

Question

What is the best way to wait for multiple asynchronous callback functions to finish in Java before continuing. Specifically I\'m using GWT with AsyncCallback, but I think this i

Answer 1

I wrote two classes that solve this problem on my project. Basically, each individual callback registers with a parent. The parent waits for each child callback to complete, then fires off it's own handleSuccess().

The client code looks like this:

public void someGwtClientSideMethod() {
    SomeServiceAsync someService = GWT.create(SomeService.class);
    ParallelCallback fooCallback = new ParallelCallback();
    ParallelCallback barCallback = new ParallelCallback();
    ParentCallback parent = new ParentCallback(fooCallback, barCallback) {
        public void handleSuccess() {
            doSomething(getCallbackData(1), getCallbackData(2));
        }
    };
    someService.foo(fooCallback);
    someService.bar(barCallback);
}

I wrote a post explaining it here: Parallel Asynchronous Calls in GWT. The implementation for these two classes is linked from that post (sorry, can't give links here because I'm a newbie user - not enough karma to include more than one link!).