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From "Fernando (JIRA)" <j...@apache.org>
Subject [jira] Commented: (OPENJPA-825) slices: hangs with multithreaded true
Date Mon, 15 Dec 2008 17:27:44 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-825?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12656666#action_12656666
] 

Fernando commented on OPENJPA-825:
----------------------------------

I have to add that because Slices does execute the Query using multiple threads ( ST1, ST2,
ST3 mentioned above ).  It is explicitly accessing the EM in a multi-threaded manner, thus
breaking the whole assumptions that you can only access the EM with one thread.

THUS:

Slices REQUIRES openjpa.Multithreaded=true !!!!!!!!!!!!

Conceptually, if you will be executing the EM with multiple threads, you have to use openjpa.Multithreaded=true.
 And if you don't you will see corruption and weird behavior, which another issue (OPENJPA-820)
shows exactly that Slices with openjpa.Multithread=false can have erratic behavior, with invalid
results for queries.  Thus if you run Slices with openjpa.Multithreaded=false, then any query
you run could be returning invalid values!

I just wanted to go on record stating that this bug (OPENJPA-825) is an either/or proposition,
or only an issue if you run with openjpa.Multithreaded=true, because currently Slices requires
openjpa.Multithreaded=true.  Thus though the easy solution is #1, that is the most un-performant
of any of them, so it's a great short-term solution.  And #3 is useless because deadlocks
ARE GUARANTEED to occur (OPENJPA-820), because most of the code uses a global lock, there
is no way around deadlocks.  #2 is the only long-term solution...


> slices: hangs with multithreaded true
> -------------------------------------
>
>                 Key: OPENJPA-825
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-825
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: kernel
>    Affects Versions: 2.0.0
>            Reporter: Fernando
>            Assignee: Pinaki Poddar
>            Priority: Critical
>         Attachments: hang-multithread.jstack, hang-multithread.txt
>
>
> When I turned on openjpa.Multithreaded as a possible fix for another bug, I see that
the system hangs.  Attached are going to be a log file, and jstack, showing how it system
hung on the very first query. ( it did execute a few find() operations, but those are not
executed via ParallelExecutor ).

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