PM38422: POTENTIAL DEADLOCK IN OPENJPA WITH OBJECT RELATIONAL MAPPING (ORM) PROCESSING

6.1.0.47: WebSphere Application Server V6.1 Fix Pack 47
6.1.0.43: Java SDK 1.5 SR13 Cumulative Fix for WebSphere Application Server
6.1.0.45: Java SDK 1.5 SR14 Cumulative Fix for WebSphere Application Server
6.1.0.47: Java SDK 1.5 SR16 Cumulative Fix for WebSphere Application Server

APAR status

• Closed as program error.

Error description

• The potential for deadlock exists 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.
  

Local fix

• N/A
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:  All users of IBM WebSphere Application      *
  *                  Server Feature Pack for EJB 3.0             *
  ****************************************************************
  * PROBLEM DESCRIPTION: Potential for deadlock 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 guerentees 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 6.1.0.43.  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 is sysrouted FROM one or more of the following:

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

  PM38854 PM65860

Fix information

• Fixed component name

  WAS EJB3 FEATUR

• Fixed component ID

  5724J0851

Applicable component levels

• R610 PSY

     UP