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From "Jody Grassel (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (OPENJPA-1993) Deadlock Potential with ORM XML Processing
Date Wed, 04 May 2011 22:38:03 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-1993?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13029019#comment-13029019
] 

Jody Grassel commented on OPENJPA-1993:
---------------------------------------

Checked in the fix for this issue.  To preserve original behavior, the ContextClassLoader
override will only take place if the following OpenJPA Compatibility option is set:

openjpa.Compatibility="OverrideContextClassloader=true"

> Deadlock Potential with ORM XML Processing
> ------------------------------------------
>
>                 Key: OPENJPA-1993
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-1993
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: kernel
>    Affects Versions: 1.0.0, 1.0.1, 1.0.2, 1.0.3, 1.0.4, 1.2.0, 1.2.1, 1.2.2, 2.0.0, 2.0.1,
2.1.0
>            Reporter: Jody Grassel
>            Assignee: Jody Grassel
>
> There exists the potential for deadlock with the ORM XML processing function.  In an
environment
> with multiple threads (such as an application server), operations (such as creating a
new
> EntityManagerFactory or transformation Classloader activity) can lead to a point where
> a Xerces SAX Parser (acquired by XMLFactory) is constituted and executed.  Xerces calls

> Thread.currentThread().getContextClassloader() during its execution to construct the
> SAXParser (via ObjectFactory.createObject()).  This means that within the call to Xerces,
> a ClassLoader lock will be attempted on the Thread's ContextClassLoader.  If there is
already
> a lock with a ClassLoader higher in the heirarchy, and another thread with a lock on
the
> same ContextClassLoader that is waiting to acquire a lock on a higher level ClassLoader,
then
> a deadlock will occur.
> A solution to this problem is to temporally set the Thread's ContextClassLoader at the
> point where XML APIs are invoked (such as in XMLFactory, XMLMetaDataParser) to the
> ClassLoader that loaded the OpenJPA implementation classes.  This will prevent Xerces
from
> starting with a lower level classloader and avoid this deadlock potential.

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