PM38854: POTENTIAL DEADLOCK IN OPENJPA WITH OBJECT RELATIONAL MAPPING (ORM) PROCESSING

Fixes are available

APAR status

Closed as program error.

Error description

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.

Local fix

```
N/A
```

Problem summary

****************************************************************
* USERS AFFECTED:  All users of IBM WebSphere Application      *
*                  Server V7.0 and V8.0                        *
****************************************************************
* PROBLEM DESCRIPTION: The potential for deadlock exists with  *
*                      the ORM XML processing                  *
*                      function.                               *
****************************************************************
* RECOMMENDATION:                                              *
****************************************************************
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 run. 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.
The deadlock occurs when a thread locks the compound
classloader (which can occur when the transformation
classloader is invoked) and xerces is called upon by the
OpenJPA PCEnhancer to parse an ORM XML. Xerces will use the
ClassLoader specified by the Thread's ContextClassLoader to
find SAX/DOM Parser implementations, which means its
ClassLoader activity will attempt to lock the Thread's
ContextClassLoader.  In this situation, the ContextClassLoader
is the classloader at the bottom of the heirarchy, such as the
web container's application classloader.  The deadlock can
occur if another thread performs a ClassLoader operation that
locks the web container application classloader and makes a
further attempt to lock a higher classloder (ie, the compound
classloader).  This results in a deadlock between the two
threads.

Problem conclusion

The solution is to change the Thread ContextClassLoader to the
classloader used to load the OpenJPA implementation classes
which guarantees that Xerces will use a ClassLoader that is
higher up the ClassLoader heirarchy.

An interim Fix is available to fix this problem.  In addition
to installing the interim Fix, the following property must be
set to enable the ContextClassLoader override in either the
persistence unit definition within persistence.xml or as a
server JVM property:

=========================================
Name:   openjpa.Compatibility
Value:  OverrideContextClassloader=true
=========================================

The fix for this APAR is currently targeted for inclusion in
fix pack 7.0.0.23 and 8.0.0.3.  Please refer to the Recommended
Updates page for delivery information:
http://www.ibm.com/support/docview.wss?rs=180&uid=swg27004980

Temporary fix

Comments

APAR Information

APAR number
PM38854
Reported component name
WEBSPHERE APP S
Reported component ID
5724J0800
Reported release
700
Status
CLOSED PER
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt
Submitted date
2011-05-10
Closed date
2012-02-16
Last modified date
2012-02-16

APAR is sysrouted FROM one or more of the following:

PM38422
APAR is sysrouted TO one or more of the following:

Fix information

Fixed component name
WEBSPHERE APP S
Fixed component ID
5724J0800

Applicable component levels

R700 PSY
UP
R800 PSY
UP

[{"Business Unit":{"code":"BU059","label":"IBM Software w\/o TPS"},"Product":{"code":"SSEQTP","label":"WebSphere Application Server"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"7.0","Line of Business":{"code":"LOB45","label":"Automation"}}]

Document Information

Modified date:
27 October 2021

Tips

PM38854: POTENTIAL DEADLOCK IN OPENJPA WITH OBJECT RELATIONAL MAPPING (ORM) PROCESSING

Fixes are available

Subscribe

APAR status

Closed as program error.

Error description

Local fix

Problem summary

Problem conclusion

Temporary fix

Comments

APAR Information

APAR number

Reported component name

Reported component ID

Reported release

Status

PE

HIPER

Special Attention

Submitted date

Closed date

Last modified date

APAR is sysrouted FROM one or more of the following:

APAR is sysrouted TO one or more of the following:

Fix information

Fixed component name

Fixed component ID

Applicable component levels

R700 PSY

R800 PSY

Document Information

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