IJ49047: JAVA JIT: REORDERING CODE WITH A CALL TO CURRENTTIMEMILLIS() CAN RESULT IN INACCURATE RESULTS

APAR status

• Closed as program error.

Error description

• Error Message: The difference between two calls to
  currentTimeMillis() would result in impossible results.
  .
  Stack Trace: N/A
  .
  The problem can only occur when running the Java JVM under zOS.
  The issue is not possible on other platforms including zLinux.
  

Local fix

• The problem can be avoided by using the following java command
  line parameter:
  -Xjit:disableTreeSimplification
  Using this options will have some effect on the performance of
  the application.
  

Problem summary

• The JIT converts a call to currentTimeMillis() into a a special
  System-Z instruction, but in doing so, the internal
  representation of the code was setup in an incorrect way that
  allowed another JIT optimization to move the code around. This
  might result in a delayed execution of the Z instruction by
  moving it after other calls. This delay might cause incorrect
  and unexpected time calculations.
  

Problem conclusion

• The JIT was modified so that a methods internal representation
  is correct after currentTimeMillis() conversion on zOS
  preventing any incorrect code motion.
  .
  This APAR will be fixed in the following Releases:
  .
  IBM Semeru Runtimes
     11              11.0.22.0
     17              17.0.10.0
  IBM SDK, Java Technology Edition
     8    SR8 FP20  (8.0.8.20)
  .
  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