Re: PCRegistry ClassLoader memory leak

[Kevan Miller]

I've attached two patches to https://issues.apache.org/jira/browse/ 
OPENJPA-285. I've tested deploy/undeploy scenarios with the two  
patches. They appear to clear up ClassLoader memory leaks associated  
with deployment/undeployment of applications.

The patch to ImplHelper is straight-forward, IMO. _assignableTypes  
maintains a Map of Class, Map pairs. The Class key is WEAK. The  
assignableTo Maps need to use WEAK keys, also. Otherwise, there is a  
chain of HARD references which will prevent GC of the 'to' Class'  
ClassLoader.

The PCRegistry change was the subject of earlier discussion. I see no  
mechanism of WeakReferences/Stringified object names that would  
permit the appropriate Garbage Collection of the Meta.pc object (and  
it's associated ClassLoader). Instead, this patch adds a  
PCRegistry.deregister(ClassLoader) method. When a ClassLoader is no  
longer viable, Embedders may use this method to cause PCRegistry to  
remove Meta objects from the _metas Map.

My testing shows that these two patches clear up the ClassLoader  
memory leaks (at least in the scenarios I've tested). Hoping that we  
can get these patches applied...

Thanks!

--kevan