IJ08850: JAVA JIT: CRASH IN ARRAYLIST$ITR.NEXT()

APAR status

• Closed as program error.

Error description

• Error Message: SIG_SEGV when executing in code for
  java/util/ArrayList$Itr.next() on POWER platforms.
  .
  Stack Trace: Looking at the javacore from the crash the
  "Current thread" stack trace looks like this:
  3XMTHREADINFO3    Java callstack:
  4XESTACKTRACE         at
  java/util/ArrayList$Itr.next(ArrayList.java:878(Compiled Code))
  .
  The problem can only surface when an array of objects is
  allocated at the very end of the java heap memory space and that
  object array is being accessed using the Iterator object
  returned from ArrayList.iterator()
  i.e.
     static void test(ArrayList numbers){
        Iterator<String> itr = numbers.iterator();
        while( itr.hasNext() ){
           System.out.println("Itr: " + itr.next() );
        }
        System.out.println("\n");
     }
  This issue involving ArrayList$Itr.next() can only happen in
  Java 8.0.5.17, 8.0.5.20 and 8.0.5.21 but a similar issue
  involving TreeMap$UnboundedValueIterator.next() can happen in
  previous releases. The chances of hitting the TreeMap problem
  were increased in Java 8.0.5.17 because of a change in the
  prefetching stride distance. Both issues are addressed by the
  same fix. The issue only effects POWER (PowerPC) platforms (AIX
  and Linux on PPC)
  

Local fix

• You can only avoid the problem by preventing the JIT from
  compiling and inlining two specific methods using the following
  command line option:
  -Xjit:exclude={java/util/ArrayList$Itr.next*|java/util/Tree
  Map$UnboundedValueIterator.next*},dontInline={java/util/ArrayLis
  t$Itr.next*|java/util/TreeMap$UnboundedValueIterator.next*}
  The above option should only have a minor effect on performance
  for most applications.
  
  Note that depending on how the option is provided and the
  environment that the command is running in, it may be necessary
  to escape the $ characters to prevent them being processed by
  the shell.
  

Problem summary

• When attempting to load the CPU cache with the contents of
  objects that we expect to be accessed in the near future, the
  JIT could run off the end of an object array leading to a crash
  when that array is allocated at very the end of the addressable
  memory space.
  

Problem conclusion

• The JIT was modified so that it will only attempt to load the
  CPU cache when it's known to be safe to do so.
  .
  This APAR will be fixed in the following Java Releases:
     8    SR5 FP22  (8.0.5.22)
  .
  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