IJ42263: JAVA JIT, UNEXPECTED CLASSCASTEXCEPTION

APAR status

• Closed as program error.

Error description

• Error Message: An Intermittent ClassCastException is thrown.
  Other symptoms are also possible depending on how the java code
  was written to respond to the return value when calling
  Class.instanceOf().
  .
  Stack Trace: N/A
  .
  This issue can only occur on the POWER version of the J9 JVM
  (AIX and LinuxPCC, LinuxPPCle). All other architectures are not
  effected by this issue.
  The issue was first introduced in Java 8.0.6.36, earlier version
  of the J9 JVM are not subject to this issue.
  The issue only effects methods that contain a call to
  Class.instanceOf(), the instanceof keyword is not effected. In
  addition, the type of the class must not be statically knowable
  in order for the problem to occur.
  

Local fix

• The issue can be avoided by using the following java command
  line argument:
  -Xjit:disableInlineIsInstance
  This will have a minor effect on performance when handling some
  types of cases where the JIT needs to do an instanceof check
  (but it's not limited to just Class.instanceOf() calls).
  You can reduce the performance cost by limiting this option so
  it only effects the method that is known to trigger this issue:
  -Xjit:{pkg/class.method*}(disableInlineIsInstance)
  Where "pkg/class.method" is replaced with the full name of the
  effected method.
  

Problem summary

• When the JIT compiles a method with a call to Class.isInstance()
  the code might return an incorrect result. Specifically, it may
  return True when it should be False.
  

Problem conclusion

• The JIT was modified to prevent it from incorrectly returning
  True.
  .
  This APAR will be fixed in the following Releases:
  .
  IBM SDK, Java Technology Edition
     8    SR6 FP20  (8.0.6.20)
  .
  Contact your IBM Product's Service Team for these Service
  Refreshes and Fix Packs.
  For those running stand-alone, information about the available
  maintenance can be found at:
             https://www.ibm.com/support/pages/java-sdk
  

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

  JIT

• Fixed component ID

  620700124

Applicable component levels