[FELIX-2653] LinkageError caused by duplicate class definition during implicit boot delegation

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: framework-3.0.4
• Fix Version/s: framework-3.0.5
• Component/s: Framework
• Environment: java version "1.6.0_21"; Java(TM) SE Runtime Environment (build 1.6.0_21-b06); Java HotSpot(TM) Server VM (build 17.0-b16, mixed mode)
• Assignee: Richard S. Hall
• Reporter: Sanjeeb Kumar Sahoo
• Created: 12/Oct/10 10:19
• Updated: 15/Oct/10 18:03
• Resolved: 12/Oct/10 19:40

Description

I am seeing linkage errors caused by attempt to load duplicate classes and I think it is caused by implicit boot delegation. In our server log, we see the following exception stack:

java.lang.LinkageError: loader (instance of java/net/URLClassLoader): attempted duplicate class definition for name: "com/acme/Foo"
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
at com.acme.Foo$Factory.bar(Foo.java:93)

I tried to trace the execution to find out what causes the class to be defined for the first time and with the help of btrace (http://projectkenai.com/projects/btrace/), I could obtain the stack and relevant information. First time the class is defined, the stack looks like this:

java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
java.net.URLClassLoader.access$000(URLClassLoader.java:58)
java.net.URLClassLoader$1.run(URLClassLoader.java:197)
java.security.AccessController.doPrivileged(Native Method)
java.net.URLClassLoader.findClass(URLClassLoader.java:190)
java.lang.ClassLoader.loadClass(ClassLoader.java:307)
java.lang.ClassLoader.loadClass(ClassLoader.java:248)
org.apache.felix.framework.ModuleImpl.getEnclosingClass(ModuleImpl.java:1570)
org.apache.felix.framework.ModuleImpl.isClassNotLoadedFromBundle(ModuleImpl.java:1545)
org.apache.felix.framework.ModuleImpl.doImplicitBootDelegation(ModuleImpl.java:1498)
org.apache.felix.framework.ModuleImpl.searchDynamicImports(ModuleImpl.java:1452)
org.apache.felix.framework.ModuleImpl.findClassOrResourceByDelegation(ModuleImpl.java:727)
org.apache.felix.framework.ModuleImpl.access$300(ModuleImpl.java:73)
org.apache.felix.framework.ModuleImpl$ModuleClassLoader.loadClass(ModuleImpl.java:1733)
java.lang.ClassLoader.loadClass(ClassLoader.java:248)
org.apache.felix.framework.ModuleImpl.getClassByDelegation(ModuleImpl.java:638)
org.apache.felix.framework.Felix.loadBundleClass(Felix.java:1599)
org.apache.felix.framework.BundleImpl.loadClass(BundleImpl.java:904)
org.jvnet.hk2.osgiadapter.OSGiModuleImpl$3$1.run(OSGiModuleImpl.java:399)
java.security.AccessController.doPrivileged(Native Method)
org.jvnet.hk2.osgiadapter.OSGiModuleImpl$3.loadClass(OSGiModuleImpl.java:395)
java.lang.ClassLoader.loadClass(ClassLoader.java:248)
com.sun.enterprise.v3.server.APIClassLoaderServiceImpl$APIClassLoader.loadClass(APIClassLoaderServiceImpl.java:169)
java.lang.ClassLoader.loadClass(ClassLoader.java:296)
java.lang.ClassLoader.loadClass(ClassLoader.java:248)
com.acme.Foo$Factory.bar(Foo.java:93)

As you can see, when bar method is called, VM tries to load com.acme.Foo.class and the call reaches org.apache.felix.framework.ModuleImpl.getEnclosingClass. getEnclosingClass actually causes the enclosing class, com.acme.Foo, to be defined. So, VM actually records this new class in loaded classes cache of the appropriate loader, but Felix does not consult the loaded classes cache again before trying to define the class.