Hi, I just ran into the famous deadlock with Java 6 where the same class is being loaded from two different bundles (also see FELIX-3953). This happened on a startup of a CQ instance.
I'll add more analysis details but my question is: what is the suggested best practice to handle this issue? * Use '-XX:+UnlockDiagnosticVMOptions -XX:+UnsyncloadClass' as suggested in [0] and [1]? But then again [1] says "You must treat it as unstable, experimental, temporary, unsupported". * Or would it be worth while to reconsider fixing FELIX-3953? Here's more details (see thread-dumps below): * Thread 158 (on behalf on bundle X) wants to load class A which is part of bundle Y - hence goes via getClassByDelegation - then does a BundleWiringImpl$BundleClassLoader.findClass * before Thread 158 continues VM threading decides to give Thread 156 some execution time: * Thread 156 now wants to load same class A, but this time directly on behalf of bundle Y. * Due to [1] Thread 156 internally does a synchronized loadClassInternal, thus holds the lock on 6f025d710 (the BundleClassLoader of bundle Y) (I was able to verify this by hooking the deadlocked-VM to a debugger, which indicated exactly this) * Thread 156 now continues into BundleClassLoader.findClass(BundleWiringImpl.java:2115) where it has to do a m_classLocks.wait() - since Thread 158 earlier marked the BundleClassLoader 'in use/locked for class A'. * Thread 158 on the other hand continues the findClass execution, eventually walks into checkCerts, which is synchronized(this), which Thread 156 holds * and we have the famous classloading deadlock. Cheers, Stefan -- [0] https://issues.apache.org/jira/browse/FELIX-3953 [1] http://underlap.blogspot.de/2006/11/experimental-fix-for-sunbug-4670071.html PS: Used org.apache.felix.framework 4.3.0.R1558704 - which is a snapshot-release as of SVN revision 1558704 "Thread-158" daemon prio=5 tid=7f83a4cbd800 nid=0x25b73e000 waiting for monitor entry [25b73c000] java.lang.Thread.State: BLOCKED (on object monitor) at java.lang.ClassLoader.checkCerts(ClassLoader.java:788) - waiting to lock <6f025d710> (a org.apache.felix.framework.BundleWiringImpl$BundleClassLoaderJava5) at java.lang.ClassLoader.preDefineClass(ClassLoader.java:493) at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631) at java.lang.ClassLoader.defineClass(ClassLoader.java:621) at org.apache.felix.framework.BundleWiringImpl$BundleClassLoader.findClass(BundleWiringImpl.java:2297) at org.apache.felix.framework.BundleWiringImpl.findClassOrResourceByDelegation(BundleWiringImpl.java:1519) at org.apache.felix.framework.BundleWiringImpl.access$400(BundleWiringImpl.java:77) at org.apache.felix.framework.BundleWiringImpl$BundleClassLoader.loadClass(BundleWiringImpl.java:1973) at java.lang.ClassLoader.loadClass(ClassLoader.java:247) at org.apache.felix.framework.BundleWiringImpl.getClassByDelegation(BundleWiringImpl.java:1392) at org.apache.felix.framework.BundleWiringImpl.searchImports(BundleWiringImpl.java:1571) at org.apache.felix.framework.BundleWiringImpl.findClassOrResourceByDelegation(BundleWiringImpl.java:1502) at org.apache.felix.framework.BundleWiringImpl.access$400(BundleWiringImpl.java:77) at org.apache.felix.framework.BundleWiringImpl$BundleClassLoader.loadClass(BundleWiringImpl.java:1973) at java.lang.ClassLoader.loadClass(ClassLoader.java:247) [class A being loaded from a class of bundle X] "Thread-156" daemon prio=5 tid=7f83a57ac800 nid=0x25b36b000 in Object.wait() [25b369000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) at java.lang.Object.wait(Object.java:485) at org.apache.felix.framework.BundleWiringImpl$BundleClassLoader.findClass(BundleWiringImpl.java:2115) - locked <6f788bf40> (a java.util.HashMap) at org.apache.felix.framework.BundleWiringImpl.findClassOrResourceByDelegation(BundleWiringImpl.java:1519) at org.apache.felix.framework.BundleWiringImpl.access$400(BundleWiringImpl.java:77) at org.apache.felix.framework.BundleWiringImpl$BundleClassLoader.loadClass(BundleWiringImpl.java:1973) at java.lang.ClassLoader.loadClass(ClassLoader.java:247) [class A being loaded from a class of bundle Y]
