IV34570: THE ADJUSTMENT OF COMPUTER CLOCK WHILE JAVA PROGRAM IS RUNNING C AN CREATE AN EFFECT OF 'TIME GOES BACKWARDS'

APAR status

• Closed as program error.

Error description

• Error Message: JVMDUMP039I Processing dump event "systhrow",
  detail "java/lang/OutOfMemoryError" at 2012/04/01 23:28:40 -
  please wait.
  JVMDUMP032I JVM requested System dump using
  '/tmp/bld_106960/cmdLineTester_classesdbgddrext/106026550/core.2
  0120401.232840.21717.0001.dmp' in response to an event
  JVMDUMP010I System dump written to
  /tmp/bld_106960/cmdLineTester_classesdbgddrext/106026550/core.20
  120401.232840.21717.0001.dmp
  JVMDUMP032I JVM requested Heap dump using
  '/tmp/bld_106960/cmdLineTester_classesdbgddrext/106026550/heapdu
  mp.20120401.232840.21717.0002.phd' in response to an event
  JVMDUMP010I Heap dump written to
  /tmp/bld_106960/cmdLineTester_classesdbgddrext/106026550/heapdum
  p.20120401.232840.21717.0002.phd
  JVMDUMP032I JVM requested Java dump using
  '/tmp/bld_106960/cmdLineTester_classesdbgddrext/106026550/javaco
  re.20120401.232840.21717.0003.txt' in response to an event
  JVMDUMP010I Java dump written to
  /tmp/bld_106960/cmdLineTester_classesdbgddrext/106026550/javacor
  e.20120401.232840.21717.0003.txt
  JVMDUMP032I JVM requested Snap dump using
  '/tmp/bld_106960/cmdLineTester_classesdbgddrext/106026550/Snap.2
  0120401.232840.21717.0004.trc' in response to an event
  JVMDUMP010I Snap dump written to
  /tmp/bld_106960/cmdLineTester_classesdbgddrext/106026550/Snap.20
  120401.232840.21717.0004.trc
  JVMDUMP013I Processed dump event "systhrow", detail
  "java/lang/OutOfMemoryError".
  Exception in thread "Thread-20" java.lang.OutOfMemoryError: Java
  heap space
   at
  java.lang.StringBuffer.ensureCapacityImpl(StringBuffer.java:338)
   at java.lang.StringBuffer.append(StringBuffer.java:204)
   at Test$StreamMatcher.run(Unknown Source)
  .
  Stack Trace: N/A
  .
  "!!! The external wall clock shift (backwards) detected !!!"
  message in GC verbose log
  

Local fix

• This is extremely intermittent issue occur if computer clock was
  adjusted while Java program was running. This is
  -Xgcpolicy:gencon specific issue, so this issue can be worked
  around using another GC policy or just re-running Java program.
  

Problem summary

• An adjustment of computer clock while Java program is running
  can create an effect of "time goes backwards" when GC End time
  is earlier then GC Start time. This might be a reason for
  mistake in calculation of duration of GC Cycle (very large
  number). The result of this might be unnecessary throwing OOM or
  even crash in Java VM
  

Problem conclusion

• This defect will be fixed in:
  7.0.0 SR3
  6.0.1 SR4
  .
  Added detection of "time goes backwards" situation and adjust
  required calculations.
  

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

  J9 COMMON CODE

• Fixed component ID

  620700127

Applicable component levels

• R260 PSY

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