Classes not unloading correctly?

[Tony Printezis]

Great to see a second Kessler on this list! Welcome, Jacob.

Tony

Jacob Kessler wrote:
> I'm working on the GlassFish scripting project, trying to solve an issue 
> with the PermGen around deploying and undeploying applications.
>
> We use an embedded JRuby interpreter to host each deployed Ruby 
> application, and JRuby makes extensive use of JIT-ed classes to improve 
> performance. A typical JRuby instance takes roughly 20MB of permgen. 
> We'd like for that space to be reclaimed once the application is 
> undeployed, since losing 20MB of permgen each time an application is 
> deployed puts a fairly hard limit on the number of redeploys that the 
> server can take before it has to be restarted.
>
> We started out using -XX:+UseConcMarkSweepGC and 
> -XX:+CMSClassUnloadingEnabled, and with the aid of a memory analysis 
> tool (YourKit), we confirmed that some classes were being unloaded (not 
> a significant number, though), and we tracked down and fixed two things 
> that were improperly holding references to the classloader that 
> contained JRuby. After fixing those, though, we ended up in a situation 
> where YourKit was reporting the classes as still in memory after a 
> forced full collection, but as having no paths to the GC roots. This 
> situation seemed able to persist indefinitely (so, beyond time for the 
> finalizer queue to drain). Does anyone have any ideas on what might be 
> preventing the classloader from collecting?
>
> I'm using
> $java -version
> java version "1.6.0_07"
> Java(TM) SE Runtime Environment (build 1.6.0_07-b06)
> Java HotSpot(TM) 64-Bit Server VM (build 10.0-b23, mixed mode)
>
> Thank you for any help with this.
>
> _______________________________________________
> hotspot-gc-use mailing list
> hotspot-gc-use at openjdk.java.net
> http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use
>   

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