[jboss-user] [JBoss AOP Development] New message: "Re: ClassPool Refactoring"

[Flavia Rainone]

User development,

A new message was posted in the thread "ClassPool Refactoring":

http://community.jboss.org/message/525602#525602

Author  : Flavia Rainone
Profile : http://community.jboss.org/people/flavia.rainone@jboss.com

Message:
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All tests are passing now in my system, which allowed me to validate two previous fixes Kabir and I implemented for the problem of duplicate CtClasses.
Kabir's fix consists of https://jira.jboss.org/jira/browse/JBAOP-766 :
 
public class DelegatingClassPool extends BaseClassPool
{
...
 public CtClass getCached(String classname)
   {
>>>      //TODO Not 100 sure this is correct, but it seems to do the job where repeated calls to get() on a pool in a hierarchy returns a different instance of the class
>>>      CtClass clazz = super.getCachedLocally(classname);
>>>      if (clazz != null)
>>>         return clazz;  
      
      if (isGeneratedClass(classname))
      {
         return null;
      }
      return domain.getCachedOrCreate(this, classname, false);
   }
}

 
 
My fix has never been comitted and consists of adding a check on the classes cache to BaseClassPool.get:
 
public class BaseClassPool extends AbstractClassPool
{
 ...
 @Override
   public final CtClass get(String classname) throws NotFoundException 
   {
      boolean trace = logger.isTraceEnabled();
      if (trace) logger.trace(this + " initiating get of " + classname);
 
      if (this.getClassLoader() == null)
      {
         throw new IllegalStateException("Illegal call. " + " A class cannot be retrieved from ClassPool " +
                                         this + " because the corresponding ClassLoader is garbage collected");
      }
      try
      {
>>>         if (this.classes.containsKey(classname))
>>>         {
>>>            return (CtClass) classes.get(classname); 
>>>         }
         CtClass clazz = super.get(classname);
         if (trace)
            logger.trace(this + " completed get of " + classname + " " + getClassPoolLogStringForClass(clazz));
 
         return clazz;
      }
      catch (NotFoundException e)
      {
         if (trace)
            logger.trace(classname + " could not be found from " + this, e);
         throw e;
      }
   }
}

 

It turns out that, once all tests were fixed for issue https://jira.jboss.org/jira/browse/JBREFLECT-94, those fixes weren't needed anymore, which means that JBREFLECT-94 was the real issue.
 
Now I'm left with the dillema of whether should I commit those fixes. I have started running some tests to try to figure out if any of those bring some improvement, and it seems that looking up classes cache in BaseClassLoader.get does bring a few improvements to the performance of aop tests, but I need to run those tests more times in order to do a reasonable investigation.
 
While working with Kabir to fix the AOP tests for AS, he pointed out that there could be an issue related to my fix. It seemed obviously right to me to look in the classes cache (a cache declared in ScopedClassPool that contains all classes created by the current class pool) before doing anything else. To me, if we have a hit in the cache, it means that the current pool is the one that is supposed to load the class, and that there is no need to look further by calling super.get method. But Kabir raised the following possibility. What if the class pool scenario (a reflection of the class loader/domain scenario) changes after the current class pool loaded the class, in a way that this class pool is no longer the one responsible for loading that class? In that case, looking for the class in the classes cache would be a serious mistake. Is this scenario possible?
 
Regarding Kabir's fix, I'm also looking for any opnion regarding whether it should be committed. It seems, though, that adding both fixes brings some small performance penalty. I'll continue running tests to be able to assert whether this is really true, and what is the penalty we're talking about.

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