EAP 6 classloader deadlocks on JRockit JVM

Solution Unverified - Updated

Environment

  • JBoss Enterprise Application Platform (EAP) 6.x
  • JRockit 1.6

Issue

  • EAP 6 deadlocks in classloading on the JRockit JDK like so:

"ServerService Thread Pool -- 327" id=805 idx=0x7b4 tid=24043 prio=5 alive, blocked, native_blocked
    -- Blocked trying to get lock: org/jboss/modules/ModuleClassLoader@0x6bcfcf18[fat lock]
    at jrockit/vm/Threads.waitForUnblockSignal()V(Native Method)
    at jrockit/vm/Locks.fatLockBlockOrSpin(Locks.java:1411)
    at jrockit/vm/Locks.lockFat(Locks.java:1512)
    at jrockit/vm/Locks.monitorEnterSecondStageHard(Locks.java:1054)
    at jrockit/vm/Locks.monitorEnterSecondStage(Locks.java:1005)
    at jrockit/vm/Locks.monitorEnter(Locks.java:2179)
    at org/jboss/modules/ModuleClassLoader.defineClass(ModuleClassLoader.java:450)
    at org/jboss/modules/ModuleClassLoader.loadClassLocal(ModuleClassLoader.java:277)
    at org/jboss/modules/ModuleClassLoader$1.loadClassLocal(ModuleClassLoader.java:92)
    at org/jboss/modules/Module.loadModuleClass(Module.java:568)
    at org/jboss/modules/ModuleClassLoader.findClass(ModuleClassLoader.java:205)
    at org/jboss/modules/ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:459)
    at org/jboss/modules/ConcurrentClassLoader.performLoadClassChecked(ConcurrentClassLoader.java:408)
    at org/jboss/modules/ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:389)
    at org/jboss/modules/ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:134)
    at jrockit/vm/Classes.loadClassInternal(Classes.java:76)
    ^-- Holding lock: org/jboss/modules/ModuleClassLoader@0x6bcefbe0[fat lock]
    at jrockit/vm/RNI.c2java(JJJJJ)V(Native Method)
    at jrockit/vm/Classes.forName0(Ljava/lang/String;ZLjava/lang/ClassLoader;)Ljava/lang/Class;(Native Method)
    at java/lang/Class.forName0(Ljava/lang/String;ZLjava/lang/ClassLoader;)Ljava/lang/Class;(Native Method)
    at java/lang/Class.forName(Class.java:171)

"ServerService Thread Pool -- 328" id=806 idx=0x7b8 tid=24044 prio=5 alive, blocked, native_blocked
    -- Blocked trying to get lock: org/jboss/modules/ModuleClassLoader@0x6bcefbe0[fat lock]
    at jrockit/vm/Threads.waitForUnblockSignal()V(Native Method)
    at jrockit/vm/Locks.fatLockBlockOrSpin(Locks.java:1411)
    at jrockit/vm/Locks.lockFat(Locks.java:1512)
    at jrockit/vm/Locks.monitorEnterSecondStageHard(Locks.java:1054)
    at jrockit/vm/Locks.monitorEnterSecondStage(Locks.java:1005)
    at jrockit/vm/Locks.monitorEnter(Locks.java:2179)
    at org/jboss/modules/ModuleClassLoader.defineClass(ModuleClassLoader.java:450)
    at org/jboss/modules/ModuleClassLoader.loadClassLocal(ModuleClassLoader.java:277)
    at org/jboss/modules/ModuleClassLoader$1.loadClassLocal(ModuleClassLoader.java:92)
    at org/jboss/modules/Module.loadModuleClass(Module.java:568)
    at org/jboss/modules/ModuleClassLoader.findClass(ModuleClassLoader.java:205)
    at org/jboss/modules/ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:459)
    at org/jboss/modules/ConcurrentClassLoader.performLoadClassChecked(ConcurrentClassLoader.java:408)
    at org/jboss/modules/ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:389)
    at org/jboss/modules/ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:134)
    at jrockit/vm/Classes.loadClassInternal(Classes.java:76)
    ^-- Holding lock: org/jboss/modules/ModuleClassLoader@0x6bcfcf18[fat lock]
    at jrockit/vm/RNI.c2java(JJJJJ)V(Native Method)
    at jrockit/vm/RNI.generateVirtualCode(Ljava/lang/Object;JJ)J(Native Method)

Resolution

  • Set the jboss.modules.safe-jdk system property to false to disable that safe classloading mode:
-Djboss.modules.safe-jdk=false

Root Cause

  • EAP 6 classloading assumes jrockit JVMs are "safe", meaning the classloader locking done by the JVM will not pose concerns of deadlocks.
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