JRubyClassLoader not getting released

Question

We're running a small JRuby on Rails app under Tomcat 6.0.28 with a Spring-based backend. I've spent some time with the Eclipse Memory Analysis tool and I can definitely tell that instances of the JRubyClassLoader are leaking. I setup our webapp to only use a single JRuby runtime and then I effectively did a hot-deploy to Tomcat by touching the war. After doing that a few times, I can see several instances of the JRubyClassLoader sitting around.

Since the classloader isn't getting released, the classes it loaded aren't getting released and we're running out of PermGen space.

Using Eclipse Memory Analysis, I can see the path to the GC root looks like:

org.jruby.util.JRubyClassLoader
  jrubyClassLoader org.jruby.Ruby
    runtime org.jruby.util.io.ChannelStream
      reference java.lang.ref.Finalizer
        next java.lang.ref.Finalizer

And the list of next java.lang.ref.Finalizer goes on seemingly forever... to point where I can't seem to find the actual GC root.

If run the Leak Suspects report, the #1 suspect is "java.lang.ref.Finalizer", loaded by "<system class loader>".

Any ideas why the Finalizer is sticking around?

EDIT

As a possibly related side note, every time I do a hot deploy, a get a slew of NullPointerExceptions:

java.lang.NullPointerException
    at com.kenai.jffi.Function.finalize(Function.java:177)
    at java.lang.ref.Finalizer.invokeFinalizeMethod(Native Method)
    at java.lang.ref.Finalizer.runFinalizer(Finalizer.java:83)
    at java.lang.ref.Finalizer.access$100(Finalizer.java:14)
    at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:160)

EDIT 2

I upgraded to JRuby 1.5.1 and I'm still seeing the same problems.

Answer 1

interesting. another evidence that finalize() should not be used.

it's not your fault and there's not much you can do about it.

maybe try to convince JRuby team to drop finalize()? shouldn't JRuby take care of resource deallocation at the earliest time instead of waiting till GC? Developers using JRuby are not interfacing with these objects, they are all under the control of JRuby.