2009/6/15 Todor Boev <t.b...@prosyst.bg>
> Hello,
> Seems I have been chewing on the service dynamics issue forever. Just as I
> though I got a workable concept about tracking and releasing services I
> stumble
> on a contradicting concept. The problem is this:
>
> According to my understanding it is not acceptable importer behavior to
> ever
> call service objects that are unregistered. Achieving this requires the
> service
> to be tracked and every piece of code that calls the service be
> synchronized
> with the tracking code. I'll name this the "dedicated lock approach":
>
> private Object lock;
> private Hello service;
>
> void set(Hello service) {
> synchronized (lock) {
> this.service = service;
> }
> }
>
> Hello get() {
> synchronized (lock) {
> if (service == null) {
> throw new ServiceUnavailableException();
> }
> return service;
> }
> }
>
> void usefulMethod() {
> synchronized (lock) {
> get().greet("World");
> }
> }
>
> Some say we should never call out from the bundle while holding a lock but
> I
> think we are safe if we use a dedicated private lock for every tracked
> service.
> In any case I can't think of any other way to be safe at all times. Lately
> however I have been encountering the "local-cache" approach, which seems to
> state we don't need to be that paranoid. E.g.
>
> void usefulMethod() {
> Hello service = get();
>
> /* At this spot right here the service can go down! */
>
> service.greet("World");
> }
>
> Here we risk calling a service in an undetermined state. Do we expect every
> exporter to invalidate his objects to keep us safe? E.g. the exporter must
> keep
> a "closed" flag around, mark the service as invalid in a thread-safe
> manner, and
> start tossing exceptions at callers from that point on.
>
> iPojo follows the local cache approach - right Richard?
> Peaberry follows the dedicated lock approach - right Stuart?
>
nope - peaberry doesn't hold any locks during the actual service call, it
only
has a small amount of synchronization to properly manage internal records
when setting up and tearing down a service call
> I'd be grateful if you help me compare these import modes. That is if I got
> it
> right who uses what :)
>
> Cheers,
> Todor
>
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>
--
Cheers, Stuart
