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https://issues.apache.org/jira/browse/JCR-2768?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13865464#comment-13865464
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Konrad Windszus commented on JCR-2768:
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Why not using phantom references for exactly that instead of the finalizer?
They will only defer garbage collection (only as much as a finalizer) in the
case when you forgot to call logout(). You just have to listen for newly added
entries within the reference queue for weak session references and that will
only happen, if you forgot to call logout in your code. Of course you would
need another thread to actually watch for changes within the reference queue
and log the error and close the session there.
A similar approach was implemented for OSGi service references in
https://svn.apache.org/repos/asf/sling/whiteboard/justin/yamf/org.apache.sling.yamf.impl/src/main/java/org/apache/sling/yamf/impl/YamfAdapterFactory.java.
The big performance gain is, that the session can get garbage collected almost
immediately for all the cases, where the session has been correctly closed.
Only session references of unclosed sessions might live longer (but only as
long as right now all the sessions survive due to the use of the finalizer)
> Finalize method on SessionImpl
> ------------------------------
>
> Key: JCR-2768
> URL: https://issues.apache.org/jira/browse/JCR-2768
> Project: Jackrabbit Content Repository
> Issue Type: Improvement
> Components: jackrabbit-core
> Affects Versions: 2.1
> Reporter: Douglas Britsch
>
> Doing some profiling on our application which uses Jackrabbit-2.1.0 I noticed
> that there were an awful lot of java.lang.ref.Finalizer objects hanging
> around. Digging around I found the culprit was a finalize method on
> SessionImpl. While I can see what it is trying to do (close the session if
> you have not called logout) , I have found in the past that on application
> servers, finalize should be avoided for objects that are created and deleted
> frequently, as the GC behavior and object allocation is severely impacted,
> and because of the number of references held by the session this seems like
> it could keep a lot more in memory than needed a lot longer. (for more info
> see http://www.fasterj.com/articles/finalizer1.shtml ).
> Per Jukka's suggestion on the mailing list "
> The automatic closing of a discarded session and related the warning
> message are pretty useful in practice, as there are quite a few
> session leaks in many client applications. So I'd rather keep that
> functionality.
> If the finalizer causes problems, we could investigate using weak (or
> perhaps phantom) references and a reference queue for this purpose.
> The RepositoryImpl class already keeps weak references to all sessions
> in the activeSessions map, so this shouldn't even be too difficult to
> implement."
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