IJ26324: UNEXPECTED CLASSCASTEXCEPTION THROWN IN HIGH LEVEL PARALLEL APPLICATION ON IBM Z PLATFORM

APAR status

• Closed as program error.

Error description

• Error Message: "java.lang.ClassCastException"
  .
  Stack Trace:
  .
  "This issue can only occur on IBM Z (zOS/Linux on Z and
  LinuxONE) and cannot occur on POWER or x86 systems."
  

Local fix

• "Using JIT option -Xjit:maxOnsiteCacheSlotForInstanceOf=0 will
  disable the part of the code that causes the issue. If running
  with Shared Class Cache with AOT enabled, you need to first
  clear the shared class cache (See
  https://www.ibm.com/support/knowledgecenter/SSYKE2_8.0.0/openj9/
  xshareclasses/index.html#destroy-cache-utility ) and in
  subsequent runs you need to disable the optimization from both
  JIT compiled code and AOT compiled code using java options
  -Xjit:maxOnsiteCacheSlotForInstanceOf=0
  -Xaot:maxOnsiteCacheSlotForInstanceOf=0. Depending on the
  application, this workaround will have less than 1% performance
  impact on the application"
  

Problem summary

• On IBM Z, the JIT was reading/updating the instanceOf cache
  using two instructions which would allow for a race condition
  resulting in the possibility of a ClassCastException being
  thrown when two threads concurrently access the instanceOf
  cache.
  

Problem conclusion

• Compiler code has been updated to generate appropriate code to
  load and store such associated information in single operation.
  .
  This APAR will be fixed in the following Java Releases:
     8    SR6 FP15  (8.0.6.15)
  .
  Contact your IBM Product's Service Team for these Service
  Refreshes and Fix Packs.
  For those running stand-alone, information about the available
  Service Refreshes and Fix Packs can be found at:
             https://www.ibm.com/developerworks/java/jdk/
  

Temporary fix

• N/A
  

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