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From Julien Viet <jul...@jboss.com>
Subject Re: Getting "custom" objects from the repository?
Date Sat, 16 Apr 2005 22:03:49 GMT
aaahhhh I did not look at the API :-), so you are right, my bad.
I see in the source code there is a notification thread in the 
ObservationManagerFactory.

about event notification; I think that all the clients should receive 
those notifications. In the case of a local repository it is obvious it 
works. In the case of a proxy
like JCR RMI, it depends how it is coded but it could be possible to 
have it but that would need to have the client to export a remote object 
to have callbacks
(or use any other similar mechanism). I don't know if the implementation 
currently do it.

Daniel Dekany wrote:

>Saturday, April 16, 2005, 10:39:30 PM, Julien Viet wrote:
>
>  
>
>>ok for 1/ but 2/, isnt the notification synchronous ? (even if the spec
>>does not mandate it).
>>    
>>
>
>The specification says:
>
>  This specification defines only asynchronous event delivery. It is
>  possible for a repository to also implement synchronous events in
>  order to support the vetoing of changes before they happen. However,
>  this functionality is outside the scope of this specification.
>
>As it is "outside the scope of the specification", you don't even have
>Repositiry.OPTION_SYNCHRONOUS_OBSERVATION_SUPPORTED or something like
>that, so the object mapper can't check if it can work correctly over the
>JCR implementation in use or not.
>
>Then, from the API docs of javax.jcr.observation.EventListener:
>
>  An EventListener can be registered via the ObservationManager object.
>  Event listeners are notified asynchronously, and see events after they
>  occur and the transaction is committed. An event listener only sees
>  events for which the session that registered it has sufficient access
>  rights.
>
>which is absolutely not encouraging. Especially note that last sentence.
>Because, it doesn't mater who has modified the node, if it has modified,
>the cache system must realize that it is out of sync, so it never serves
>outdated objects (that would ruing the "ACID").
>  
>Then, I'm not 100% sure about this one, but I think event listeners are
>running inside the repository server, and not inside the repository
>client. And since the cache is (typically) in the client's JVM, the
>event listeners had connect back to the client's JVM somehow to send the
>notifications... lot of complication and point of failure. And if the
>event notification is synchronous, then it possibly causes serious
>performance degradation, since then the commitment of the transaction is
>done only if the event listener has completed the notification of the
>cache system.
>
>  
>


-- 
Julien Viet
JBoss Portal Lead Developer


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