Mattias Jiderhamn wrote:
> So I've spent another day hunting that lo(ooo)ng standing PermGen memory
> leak in our application and/or Resin.
>
> I made a new discovery which "shouldn't" be an issue, but could
> potentially fix problems.
> From my investigation it seems that whenever the application is
> reloaded, a reference to the old
> com.caucho.loader.EnvironmentClassLoader is kept in
> com.caucho.hessian.io.SerializerFactory._defaultFactory. I agree that in
> theory this shouldn't happen, since the ClassLoader is a weak reference
> key, /however/ if I add some code to the application shutdown,
> explicitly removing the EnvironmentClassLoader from _defaultFactory
> using reflection, the garbage collector is able to unload these classes.
>
I changed this in 4.0.2 (with some more changes in 4.0.3). Even though
the key is a weak reference, the value is a strong reference.
> I should mention though, that there is still a minimum of two
> EnvironmentClassLoaders for the given application after reloading at
> least once. The former one seem to stick around somehow. We have
> discussed this before, Scott; how references are kept inside
> com.caucho.server.dispatch.Invocation, at least in a low traffic (dev /
> debugging) environment.
On a web-app change the Invocation cache is cleared, so there shouldn't
be any old references there.
> Not sure if this a real problem, but ideally the
> class loader of the previous version should be available for garbage
> collection before the classes of the new version are loaded ('cause
> there is no turning back anyway, is there...?).
In the past this could be a problem with JNI because a JNI library can
only be loaded in one classloader (that may have been changed but it
always was a JDK restriction.)
> Otherwise you always
> have to set MaxPermSize to at least twice as much as the application
> actually needs.
>
> In some profiling session I've also seen references from logging and
> "index-cache-writer" threads, which might be worth looking into.
>
The index writer shouldn't have any references to any non-system
classloaders.
-- Scott
> Scott, could you tell me if anything can be done to the issues mentioned
> above?
>
>
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