Geoff Howard wrote:
>
> Unico,
>
> Thanks for taking a look at this with me, comments inline:
>
> Unico Hommes wrote:
> > I've checked out your event-cache code just now and like to
> make some
> > comments.
> >
> > One thing I found was that the EventRegistry.init() method
> breaks IoC
> > in Avalon. I think it's better to have initialization be
> done by the
> > Avalon container as part of lifecycle handling. This way Avalon can
> > control when the component gets initialized. Since
> EventRegistry has a
> > thread-safe lifestyle the same instance is available to other
> > components as well. A property that tells whether or not persistent
> > state was successfully regained would allow this.
>
> I agree, and at various stages on my HDD it was that way.
> IIRC the issue I never solved cleanly was the fact that it
> needed to tell the
> Cache(Store) if there was a problem retrieving persistent
> state. At the time though I was not as confident in the
> lifecycle contract regarding dealing with other components in
> initialize(). But I now think IoC can be done more cleanly
> there pretty easily.
>
> > The other thing I was wondering about is why not use Store
> component
> > in DefaultEventRegistryImpl so that it won't have to handle
> > persistence itself?
>
> I thought of that, but thought there could potentially be
> some circular issues there that I didn't have brain cycles to
> think through carefully.
> Actually, it could be the opposite: it may get rid of
> some of the issues with failing to retrieve persistent state,
> since it would either all be there together or not.
Hey yeah, I hadn't thought of that one yet :)
>
> > I have been thinking about an easy way to add all this
> functionality
> > to the pipeline and figure that a nice way to do it is to
> have a sort
> > of EventCacheGenerator that wraps any sitemap defined generator,
> > delegating al the real generating to the wrapped generator
> but taking
> > care of the handing out of Validity objects based on parameters it
> > gets from the
> > sitemap:
> >
> > <map:match pattern="blah">
> > <map:generate type="event-cache">
> > <map:parameter name="delegate" value="file" />
> > <map:parameter name="event-type" value="name-value" />
> > <map:parameter name="event-name" value="db-table" />
> > <map:parameter name="event-value" value="customers" />
> > </map:generate>
> > <map:serialize />
> > </map:match>
>
> > This way we get event-cacheable sitemap components without
> having to
> > add that functionality to each individual sitemap component.
>
> That's an excellent idea. You can see from the sample
> extended file generator in the block (which serves no purpose
> ATM) that I was thinking it would have to get handled by
> individually extending each Generator.
> Delegation would be much better.
Great.
>
> > This is actually based on a use case that came up yesterday
> from one
> > of our site developers. He uses cinclude transformer for content
> > aggregation. Some parts are generated from a backend for
> which we have
> > an event-cache equivalent system in place. The cinclude transformer
> > has only a timeout sort of caching mechanism as you may
> know, but our
> > client's case requires real-time updates so we can't use
> that. Instead
> > he needs the content-aggregating pipeline to be invalidated
> at certain
> > backend events as well. In this case probably a declaratively more
> > sound approach would be to also have a Transformer wrapper
> for event-cache.
> >
> > If you want I could code these up and send them to you? What do you
> > think?
>
> That'd be great - except it'd be better to send a patch
> through Bugzilla so I'm not the only one who can act, and so
> it doesn't get lost. When my wife & kids get back this
> afternoon I may be out of commission for a few days!
OK, I'll do that then.
There is one more thing I was thinking about earlier. The EventAware
interface could also function as a component interface. Clients that
want to send Events need to do the following now:
cache = (Cache) componentManager.lookup(Cache.ROLE);
if (cache instanceof EventAware) {
((EventAware) cache).processEvent(event);
}
Wouldn't it be better to have them say:
eventAware = (EventAware) componentManager.lookup(EventAware.ROLE);
eventAware.processEvent(event);
Regards,
Unico
