[jira] [Commented] (OPENJPA-1993) Deadlock Potential with ORM XML Processing

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    [ https://issues.apache.org/jira/browse/OPENJPA-1993?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16581454#comment-16581454 ] 

ASF subversion and git services commented on OPENJPA-1993:
----------------------------------------------------------

Commit 1838131 from dazeydev@apache.org in branch 'openjpa/branches/2.2.x'
[ https://svn.apache.org/r1838131 ]

OPENJPA-1993: Deadlock Potential with ORM XML Processing

> 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: Will Dazey
>            Priority: Major
>             Fix For: 1.2.3, 2.0.2, 2.1.2, 2.2.0, 2.3.0
>
>         Attachments: XMLMetaDataParser.patch
>
>
> 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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