IJ22300: JAVA JIT: NEW OPTION TO PREVENT ALIASING PRIMITIVE BOX CLASSES FINAL FIELDS

APAR status

• Closed as program error.

Error description

• Error Message: N/A
  .
  Stack Trace: N/A
  .
  The JIT might propagate final field initialization values to
  future uses of the final field. This means that modification of
  the final field's value might not be visible to code executed
  after the modification occurs. Final fields can be modified
  using JNI and Unsafe APIs which breaks the java language
  guarantee that final fields cannot have their values changed
  after an initial value is assigned.
  

Local fix

• With this APAR we are introducing an java command line option
  that can be used to prevent the JIT from assuming that primitive
  box class final fields are immutable.
  -Xjit:disableImmutableFieldAliasing
  This option is added to avoid problem while developers modify
  there code such that they avoid modifying primitive box class
  final fields.
  

Problem summary

• When applications use JNI or Unsafe code to modify a primitive
  box classes final field the JIT might prevent that change from
  being visible by Java code. This is the result of the JIT
  optimizing the Java code to avoid unnecessary memory operations
  based the Java specification definition of the "final" keyword
  causing fields to be immutable after initial assignment.
  

Problem conclusion

• A Java command line option was added that is used by the JIT to
  disable aliasing of primitive box class final fields.
  .
  This APAR will be fixed in the following Java Releases:
     8    SR6 FP7   (8.0.6.7)
  .
  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

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