IV30066: APPLICATION HANG DUE TO DEADLOCK BETWEEN JVM THREADS WHILE LOADI NG CLASSES FROM SIGNED JARS

APAR status

• Closed as program error.

Error description

• Error Message: Customer reported as their application getting
  hang at application startup
  .
  Stack Trace: Threads those resulted a deadlock condition are
  Thread (T1)
  "Agent Execution" J9VMThread:0x0000000012415C00,
  j9thread_t:0x00007FB62CAF43D0,
  java/lang/Thread:0x00000000119616B8, state:CW, prio=5
  
   at java/lang/Class.forNameImpl(Native Method)
   at java/lang/Class.forName(Class.java:168)
   at java/security/Provider$Service$1.run(Provider.java:831)
   at java/security/Provider$Service$1.run(Provider.java:823)
   at
  java/security/AccessController.doPrivileged(AccessController.jav
  a:203)
   at
  java/security/Provider$Service.newInstance(Provider.java:822)
  
   at
  sun/security/jca/GetInstance.getInstance(GetInstance.java:299)
   at
  sun/security/jca/GetInstance.getInstance(GetInstance.java:237)
  Thread (T2)
  "main" J9VMThread:0x00000000120DC100,
  j9thread_t:0x00007FB62C007BA0,
  java/lang/Thread:0x00000000021E4DA0, state:B, prio=5
  
    Blocked on:
  sun/misc/Launcher$ExtClassLoader@0x0000000002201BC0
    Owned by: "Agent Execution" (J9VMThread:0x0000000012415C00,
  
    java/lang/Thread:0x00000000119616B8)                        at
  java/lang/ClassLoader.loadClassHelper(ClassLoader.java:657(Compi
  led Code))
   at java/lang/ClassLoader.loadClass(ClassLoader.java:644)
   at
  sun/misc/Launcher$AppClassLoader.loadClass(Launcher.java:358)
   at java/lang/ClassLoader.loadClass(ClassLoader.java:627)
   at java/lang/Class.forNameImpl(Native Method)
   at java/lang/Class.forName(Class.java:168)
   at java/security/Provider$Service$1.run(Provider.java:831)
   at java/security/Provider$Service$1.run(Provider.java:823)
   at
  java/security/AccessController.doPrivileged(AccessController.jav
  a:203)
   at
  java/security/Provider$Service.newInstance(Provider.java:822)
   at
  sun/security/jca/GetInstance.getInstance(GetInstance.java:299)
   at
  sun/security/jca/GetInstance.getInstance(GetInstance.java:237)
  3LKMONOBJECT
  sun/misc/Launcher$ExtClassLoader@0x0000000001B90F90:
  Flat locked by "Agent Execution" (0x0000000041E8DA00), entry
  count 1
  3LKWAITERQ            Waiting to enter:3LKWAITER
  "main" (0x0000000041B5C100)
  2LKREGMON          VM class table lock (0x00007F14A4007120):
  <unowned>
  3LKNOTIFYQ            Waiting to be notified:
  3LKWAITNOTIFY            "Agent Execution" (0x0000000041E8DA00)
  .
  

Local fix

Problem summary

• In JVM class loading, there is a validation whether a class is
  already in loading process or not. A thread will wait with its
  loading process if another thread is already in progress. With
  the error scenario, one thread which is holding Extention
  ClassLoader lock and trying to load a class identifies that the
  class is already in load process by another thread and then wait
  for the class loading to complete. The second thread which is
  loading the class from a signed jar requires Extention
  ClassLoader lock and resulted in the deadlock.
  

Problem conclusion

• This defect will be fixed in:
  6.0.0 SR13
  6.0.1 SR5
  .
  IBM JVM has been modified to avoid the deadlock situation while
  loading class from signed jars.
  

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:

  PM77001

Fix information

• Fixed component name

  JAVA CLASS LIBS

• Fixed component ID

  620700130

Applicable component levels

• R600 PSY

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