PH26967: OPENJPA'S CLASS TRANSFORMER NEEDS TO RESPECT APP CLASSLOADER CONCURRENCY

APAR status

• Closed as program error.

Error description

• OpenJPA's class transformer was designed in a time when
  ClassLoader access was synchronized. Because it was assumed
  that
  if the ClassLoader caused another class to load while it was
  already enhancing a class, causing another triggering of the
  class transformer, it was assumed that that could only
  happen if
  OpenJPA was bundled as part of the application (loaded by
  the
  app classloader in an EE environment), and was safe to
  assume
  that this reentrant invocation would not be a request to
  enhance
  a persistent type, and thus return null (no enhancement
  needed).
  
  In recent releases of Liberty, the application ClassLoader
  was
  updated to allow multi-thread concurrent access as a
  performance
  improvement. Now, because the same ClassLoader (and thus
  same
  transformer), can be invoked concurrently by different
  threads,
  this assumption was no longer valid.
  

Local fix

• N/A
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:  Users of OpenJPA                            *
  ****************************************************************
  * PROBLEM DESCRIPTION: A recent performance improvement with   *
  *                      the Application Classloader allowing    *
  *                      concurrent access can cause OpenJPA to  *
  *                      miss enhancing entity types.            *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  OpenJPA's class transformer guards against reentrancy, which the
  design expected to only occur if an OpenJPA library class was
  first loaded while executing the enhance() method body.  This
  design was valid in older specifications of the JVM which
  disallowed concurrent access to a single ClassLoader.  When
  reentrancy was detected, the enhancement code was designed to
  immediately return without transforming the class (which is the
  appropriate behavior for an OpenJPA library type.). The design,
  which leveraged a simple boolean value, was insufficient for
  later JVM specifications that allowed for concurrent ClassLoader
  access.
  

Problem conclusion

• The boolean sentinel value guarding against reentrancy has been
  made thread-aware, allowing different threads (called by the
  application ClassLoader through its concurrent access) to
  concurrently enter the enhancer without rejection, while still
  enforcing non-reentrancy (for the same established reasons) on
  the same thread.
  
  The fix for this APAR is currently targeted for inclusion in
  Commercial Liberty fix pack 20.0.0.9 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:

Fix information

• Fixed component name

  LIBERTY PROFILE

• Fixed component ID

  5724J0814

Applicable component levels