4 Replies Latest reply: Apr 1, 2012 3:24 AM by Peter B RSS

Jboss AOP classloading bug

ud1 Newbie

I'm using JBoss 6.0.0 with AOP for logging user actions and function call durations. Functions of interest are marked by our custom @Trace annotation and there is an our tracing aspect, that do all the work. But sometimes, probably after jboss restart, some random functionality of the project becomes unavailable, e.g. some dropdown lists didn't working or some buttons pressing do nothing. After second rebooting everething work fine. I can't reproduce this on my machine, but customers regulary (once or twice a month) reporting about the problem. Here is the typical log with org.jboss.classpool logging on:

 

http://pastebin.com/f4TEduCB

 

When all is functioning properly the log look's like:

 

http://pastebin.com/zZKPk643

 

I have made some investigation and degugging, so probably I have found the cause of the problem.

At first, if you look at ClassPoolToDomainAdapter with a lot of byte array class paths in it, you could see the difference, at normal working this list

contains BaseClassLoader@xxxxxx{vfs:///D:/retailHub/loan/server/default/deploy/myProject.ear} ClassPath at the end, but then the problem is it doesn't.

After deepest code investigation I figured out, that this could happen then something call close() on а ClassPool, and this probably happens inside unregisterClassLoader() function.

During joint point constraction Aspect Manager calls several times unregisterClassLoader() function:

 

ClassPoolRepository

   public void unregisterClassLoader(ClassLoader classLoader)

   {

      registryHandler.unregisterClassLoader(classLoader); // <-- calls JBossClRegistryHandler.unregisterClassLoader()

      if (callbacks != null && callbacks.size() > 0)

      {

         for (ClassPoolRepositoryCallback callback : callbacks)

         {

            callback.classLoaderUnregistered(classLoader);

         }

      }

   }

 

which in turn calls JBossClRegistryHandler.registerClassLoader() functions with possible result of a closing the class pool.

 

JBossClRegistryHandler

   public ClassPool registerClassLoader(ClassLoader classLoader)

   {

      ScopedClassPool classPool = (ScopedClassPool) successor.registerClassLoader(classLoader);

      if (classPool == null) // <-- true

      {

         // TODO check this works; was delegate before

         successor.unregisterClassLoader(classLoader); // <-- calls classLoader.close()

      }

      else

      {

         Module module = getModuleForClassLoader(classLoader);

         this.registeredModules.put(module, classPool);

      }

      return classPool;

   }

 

I can't understand what is the purpose of the DefaultClassLoaderRegistryHandler, but it can return null from registerClassLoader() function,

probaly then several jointpoints are generated concurrently from different threads:

 

ClassPoolRepository$DefaultClassLoaderRegistryHandler

      public ClassPool registerClassLoader(ClassLoader classLoader)

      {

         if (classLoader == null)

         {

            classLoader = SecurityActions.getContextClassLoader();

         }

 

         if (currentClassLoaders.putIfAbsent(classLoader, Boolean.TRUE) != null)

         {

            return null; // <-- Returns null

         }

 

         ScopedClassPool classPool = (ScopedClassPool) ClassPoolRepository.super.registerClassLoader(classLoader);

         currentClassLoaders.remove(classLoader);

         return classPool;

      }

 

ScopedClassPoolRepositoryImpl:

   public void unregisterClassLoader(ClassLoader cl) {

      synchronized (registeredCLs) {

         ScopedClassPool pool = registeredCLs.remove(cl);

         if (pool != null)

            pool.close(); // <-- close

      }

   }

 

ScopedClassPool:

   public void close() {

      this.removeClassPath(classPath); // <-- remove BaseClassLoader@xxxxxx{vfs:///D:/retailHub/loan/server/default/deploy/myProject.ear} classpath

      classPath.close();

      classes.clear();

      softcache.clear();

   }

 

During joint point creation the myProject.war class loader is used, it redirects calls to JBossClClassPoolDomain, and in turn to SuperClassesFirstWeavingStrategy, and finally

the reference to the old ClassPool (with a lot of byte array class paths) is used. Is has no myProject.ear ClassLoader any more, so NotFoundException is fired.

 

I don't know how to fix this, I will appreciate your help.

  • 1. Re: Jboss AOP classloading bug
    goldm Newbie

    Hi,

     

    it seems I have a similar problem, have you found some workaround for this bug?

  • 2. Re: Jboss AOP classloading bug
    ud1 Newbie

    I simply sinchronized calls of registerClassLoader():

    I have created class:

     

     

     

    package myapp.aop;

     

    import javassist.ClassPool;

     

    import org.jboss.classpool.plugins.jbosscl.JBossClClassPoolConfig;

    import org.jboss.classpool.plugins.jbosscl.JBossClDelegatingClassPoolFactory;

    import org.jboss.classpool.spi.ClassLoaderRegistryHandler;

    import org.jboss.classpool.spi.ClassPoolRepository;

     

    import org.jboss.logging.Logger;

     

    public class ClassPoolFactory extends JBossClDelegatingClassPoolFactory

    {

    private final Logger log = Logger.getLogger(ClassPoolFactory.class);

     

    private class Handler implements ClassLoaderRegistryHandler

    {

    private ClassLoaderRegistryHandler successor;

     

    public ClassPool registerClassLoader(ClassLoader classLoader)

    {

    ClassPool result;

    synchronized(successor)

    {

    result = successor.registerClassLoader(classLoader);

    }

     

    if (result == null)

    log.debug("registerClassLoader() returned null, " + classLoader);

     

    return result;

    }

     

    public void unregisterClassLoader(ClassLoader classLoader)

    {

    successor.unregisterClassLoader(classLoader);

    }

     

    public void setSuccessor(ClassLoaderRegistryHandler handler)

    {

    successor = handler;

    }

    }

     

    public ClassPoolFactory(JBossClClassPoolConfig config)

    {

    super(config.getDomainRegistry(), config.getRegisterModuleCallback());

    config.setClassPoolFactory(this);

    ClassPoolRepository.getInstance().setClassPoolFactory(this);

    }

     

    public ClassLoaderRegistryHandler create(ClassLoaderRegistryHandler successor)

    {

    ClassLoaderRegistryHandler handler = new Handler();

    handler.setSuccessor(super.create(successor));

    return handler;

    }

    }

     

    and added these lines to the aop.xml file:

     

    ...

       <classloader name="aop-classloader" xmlns="urn:jboss:classloader:1.0" export-all="NON_EMPTY" import-all="true">

          ...

          <root>${jboss.server.home.url}/lib/myapp-aop.jar</root>

       </classloader>

     

    ...

       <bean name="MyAppClassPoolFactory" class="myapp.ClassPoolFactory">

          <constructor>

             <parameter>

                <inject bean="JBossClClassPoolConfig"/>

             </parameter>

          </constructor>

       </bean>

     

    ...

     

     

     

    Probably it should work.

  • 3. Re: Jboss AOP classloading bug
    goldm Newbie

    Thank you for quick response, I have tried it, did multiple JBoss restarts and problem didn't occured, great, you're my saviour :-)

  • 4. Re: Jboss AOP classloading bug
    Peter B Newbie

    sounds like there should be bug filled to make sure it can be fixed upstream.

    Any volunteer?