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https://issues.apache.org/jira/browse/SLING-4751?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14585780#comment-14585780
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Marc Pfaff commented on SLING-4751:
-----------------------------------
Hi
I have question related to the lazy loading and inspection of ResourceChange
objects. I assume this feature will turn ResourceChange events into resource
wrapper kind of objects. In this context, I wonder what the life cycle will be
of the underlaying resolver used by the change objects?
I'm asking because I would expect a ResourceListener implementation to have the
freedom to process the change events asynchronously. In this case I have
concerns that it's very easy for ResourceListener implementations to leave the
thread boundary of the change objects, leading to thread contention issues on
the resolver and underlaying JCR session.
The same concern applies to the prototype of
UserAwareResourceListener.onChange() with regards the passed resource resolver.
> New Observation Support
> -----------------------
>
> Key: SLING-4751
> URL: https://issues.apache.org/jira/browse/SLING-4751
> Project: Sling
> Issue Type: Improvement
> Components: API, JCR, ResourceResolver
> Reporter: Carsten Ziegeler
> Assignee: Carsten Ziegeler
> Fix For: API 2.10.0, Resource Resolver 1.2.6
>
>
> Mail thread:
> http://mail-archives.apache.org/mod_mbox/sling-dev/201505.mbox/%3C555983F2.20402%40apache.org%3E
> Starting mail
> Right now, resources changes are propagated through event admin - which
> at the time sounded like a good idea. Over time, this has shown to be a
> bottle neck.
> Basically there are at least three problems:
> - the sender of the resource events does not know whether there is a
> receiver, therefore events for each and every change need to be sent
> - event objects are immutable and therefore all relevant data needs to
> be calculated upfront, even if it's not used. For example a resource
> event contains the resource type which needs to be fetched from the
> repository, even if no one is interested in it.
> - receivers of the events can't easily act on behalf of the user who
> initiated the change.
> I created a new listener api at [1] which defines a ResourceListener
> interface and some ways how to specify the events one is interested in.
> The user aware resource listener allows to act on behalf of the user (if
> that information is available).
> On the other side, a new service, the ObservationReporter [2] is
> defined. Resource providers report changes through this interface. The
> payload of such an event is an interface which allows for lazy retrieval
> of the information.
> We can also use this mechanism for compatibility and an implementation
> of the observation reporter might sent all events via the event admin.
> [1]
> https://svn.apache.org/repos/asf/sling/whiteboard/cziegeler/api-v3/src/main/java/org/apache/sling/api/resource/observation/
> [2]
> https://svn.apache.org/repos/asf/sling/whiteboard/cziegeler
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