Re: [infinispan-dev] Async Notification API

On 05/15/2009 06:27 PM, Manik Surtani wrote: > While the new async API has been getting rave reviews, someone did > bring up async notifications. E.g., > Future f = cache.putAsync(k, v); > f.get(); > But what if I don't want to wait on f.get(), I'd rather be told > when the future is done so I can do an f.get()? In XNIO, I've solved this problem simply by using a new IoFuture type that can have notifiers registered on it, not unlike your NotifyingFuture example (which, by the way, works very well). http://anonsvn.jboss.org/repos/xnio/xnio-base/trunk/api/src/main/java/org... Notice a couple of things that I learned the hard way. future.addNotifier() accepts a notifier and an attachment (allowing the same notifier to be reused by the user if so desired). The notifier itself is called in any of three possible cases: success, cancellation (which may not apply to your use case), and failure. The notifier has a single notify method which is called in any case (an IoFuture has a getStatus() method which returns an enum value). There is an abstract class which has separate handleDone/ handleCancelled/handleFailure methods, each with an empty default implementation; this allows users to easily create anonymous classes which only implement, say, handleDone, while still allowing a single method implementation which is called when any status change occurs. Finally, the addNotifier method has a signature like this: public interface IoFuture<T> { ... <A> IoFuture<T> addNotifier(Notifier<? super T, A> notifier, A attachment); ... } This allows users to register notifiers for IoFutures of any superclass type of the result. This means, for example, that a Notifier<Object, ?> can be registered on any IoFuture, while a Notifier<Closeable, ?> can be registered on just about any IoFuture that returns an I/O entity (think async close after an operation completes). One other lesson I've learned that may be useful to you even if you opt to stick with Future<T> is that you should always use Future<? extends Whatever> rather than Future<Whatever>, and encourage your users to do the same, which gives you a little more flexibility with respect to covariance. While I doubt that IoFuture is directly applicable to your situation, hopefully you won't have to relearn the same lessons the hard way. :-) - DML