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

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!).