IV81926: FINAL FIELD OF STRING CREATED BY A STRINGBUILDER APPEARS INCORRE CTLY INITIALIZED ON A WEAK MEMORY PLATFORM

APAR status

• Closed as program error.

Error description

• Error Message: The user is most likely to report this issue as a
  NullPointerException or SIGSEGV reading a final instance field
  from a String object where that String object was created by a
  StringBuilder (either explicitly or via using the Java +
  notation). There is no reasonable expectation of the null field
  being null.
  .
  Stack Trace: N/A
  .
  The problem does not occur with -Xint and the problem only
  occurs on hardware with a weak memory ordering model - namely
  POWER hardware.
  

Local fix

• The problem can be worked around by specifying
  -Xjit:disableStringPeepholes either globally or on the affected
  method(s). This workaround is likely to reduce performance by
  about 1-2% in a typical web server scenario.
  

Problem summary

• The JIT optimizer recognizes a number of common patterns for
  StringBuilders and transforms them to use special String
  constructors for increased performance. In doing this the JIT
  added calls to various String.<init> methods without a
  subsequent allocation fence. This means that the final field
  values written by the init method are not guaranteed to be
  visible to all threads once the constructor has finished leading
  to incorrect values possibly being seen.
  

Problem conclusion

• The JIT optimizer has been enhanced to generate the necessary
  allocation fences where required to ensure final field values
  can be read reliably after the StringBuilder optimizations
  performed by the JIT.
  .
  This APAR will be fixed in the following Java Releases:
     7 R1 SR3 FP40  (7.1.3.40)
     6    SR16 FP25 (6.0.16.25)
     7    SR9 FP40  (7.0.9.40)
     6 R1 SR8 FP25  (6.1.8.25)
     8    SR3       (8.0.3.0)
  .
  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

• R130 PSY

     UP

• R600 PSY

     UP

• R260 PSY

     UP