IV91507: JAVA JIT - DEADLOCK WITH A JAVA OBJECT MONITOR

APAR status

• Closed as program error.

Error description

• Error Message: Hang with the javacore file showing a deadlock.
  Many cases show a deadlock between a StringBuffer and a
  SystemOutputStream object, but other object types are possible.
  .
  Stack Trace: N/A
  .
  The problem is most likely to occur in Java 7.1 and Java 8.0.
  It's is very unlikely to occur on Java 7.0 / 6.1 and it is only
  possible when using the -Xaggressive option on 7.0 / 6.1. The
  problem is not possible in Java 6.0.
  Typically, one of the objects involved in the deadlock will have
  a very high "entry count" as seen in the javacore.
  

Local fix

• The problem can be avoided by using the java command line option
  "-Xjit:disableMonitorCoarsening". If this option does not avoid
  the problem then this APAR is NOT the cause of the deadlock. The
  use of this option will have a very minor effect on the
  performance.
  

Problem summary

• The JIT may try to replace two adjacent monitor entry/exit
  sequences with one sequence that encapsulates the code locked by
  both sequences. In rare cases it would do this when one of the
  entry/exist sequences is inside a loop where the other sequence
  is not. This would result in the monitor entry being executed
  more then once inside the loop but only execute the monitor
  exist once, leaving the object locked incorrectly.
  

Problem conclusion

• The JIT was modified so that monitors will not be combined with
  they exist at different loop nesting levels.
  .
  This APAR will be fixed in the following Java Releases:
     7 R1 SR4       (7.1.4.0)
     6 R1 SR8 FP40  (6.1.8.40)
     7    SR10      (7.0.10.0)
     8    SR4       (8.0.4.0)
  .
  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

• R260 PSY

     UP