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From "Douglas Britsch (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCR-2768) Finalize method on SessionImpl
Date Wed, 06 Oct 2010 19:53:33 GMT

    [ https://issues.apache.org/jira/browse/JCR-2768?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12918643#action_12918643

Douglas Britsch commented on JCR-2768:

I did some investigation into using phantom references to track abandon sessions instead of
the finalize method used currently. Unfortunately keeping references to the sessions them
selfs will not work, as they have been GC'd when I am notified and I am unable to call logout
for obvious reasons. I looked a bit into using proxy objects for the SessionImpl, and that
is workable with a little overhead, but would require using cglib as there are quite a lot
of uses of the public methods on the concrete SessionImpl class. So there seems to be four
options here:
1. leave as is and take the GC hit in well behaved applications 
2. Use phantom references to the SessionImpl and log a warning when we detect an abandon session,
but dont logout the session.
3. Do some refactoring and extract an interface for the public methods of SessionImpl, then
use the jdk's Proxy as the object we hand out. Thus allowing us to cleanup the real SesionImpl
when the proxy is no longer referenced.
4. Same as above, but introduce cglib and proxy the current concrete SessionImpl. 


> 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: 2.1.0
>            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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