Re: [Springframework-developer] CGLIB memory usage within class loader

[Guillaume P. <gpo...@gl...>]

I just created a ContextListener that cleanup ThreadLocal stuff when a
webapp is shut down.  It's attached to this email if you wish to use it.

However, there's one issue I'm not sure how to deal with, that's
concurrency.  The ThreadLocal$ThreadLocalMap is accessed without
synchronization by the ThreadLocal class, because there's only one per
thread, and it's only manipulated by the owning thread.  Since my cleanup
hack might be executed from another thread, there's a risk for concurrent
access.

When reading, the problem isn't too bad.  The worse case is stale data,
which I don't even think could lead to unsuccessful cleanup, and certainly
it wouldn't corrupt other webapps.  However, once a value for a ThreadLocal
is found that needs to be cleaned, then a concurrent write is needed.
There, I cannot really see how it's possible to handle concurrency without
risk for data corruption.  The only way around this I can see is to suspend
the thread using JPDA.

Of course, if it's for development and you're the only user, then there's no
real risk of concurrency problem anyway.

Guillaume

----- Original Message ----- 
From: "Guillaume Poirier" <gpo...@gl...>
To: <spr...@li...>
Sent: Thursday, October 21, 2004 6:25 PM
Subject: Re: [Springframework-developer] CGLIB memory usage within class 
loader


>> I only wish A) there was a way to explicitly blow away the classloader
>> or B) have hibernate be redeployable.  One option is to place all the
>> Hibernate related classes inside Tomcat's shared Classloader.  This
>> might reduce the amount of times I need to restart.
>
> Well, if you care enough, I'm pretty sure you could create a 
> ContextListener
> that would cleanup when the context is destroyed.  It would invole 
> reflection
> to hack in private fields of the Threads though, so the solution might 
> fail
> in different JVM, and wouldn't work well with SecurityManagers. Basically,
> what you would have to do is to get the list of all the system's thread 
> (through
> ThreadGroup), and for each of them, iterate the "threadLocals" map, and
> the "inheritableThreadLocals", to cleanup any instance for which the
> ClassLoader is the current webapp or of child of it.
>
> You might also have to cleanup a few other things though, such as if you 
> have
> any JDBC drivers in your webapp's ClassLoader, they need to be explicitly
> unregistered, otherwise they will not be garbage collected.
>
> I create a prototype of a ContextListener that does that if you want.
>
> Guillaume
>
> ----- Original Message ----- 
> From: "Seth Ladd" <set...@gm...>
> To: <spr...@li...>
> Sent: Wednesday, October 20, 2004 2:26 PM
> Subject: Re: [Springframework-developer] CGLIB memory usage within class 
> loader
>
>
>> On Tue, 19 Oct 2004 22:10:20 -0400, Guillaume Poirier
>> <gpo...@gl...> wrote:
>>> > How does it not create a leak if the classloader is not going away?
>>> > The real cause of the OOM exceptions is that the WebappClassLoader
>>> > instances never go away.
>>>
>>> I meant if the container (e.g. Tomcat) doesn't throw the ClassLoader 
>>> away,
>>> i.e. if it's still in use...
>>> Of course, if the webapp is reloaded and the old ClassLoader isn't
>>> collected, that's a leak.
>>>
>>> What I was saying is the problem with Dom4j cause a leak when you reload 
>>> the
>>> webapp,
>>> but cause no leak if you never use hot-reload.  (While the CGLIB leak
>>> apparently does the opposite)
>>
>> Ahh... that's what I thought.  Thanks for the clarification!
>>
>> I only wish A) there was a way to explicitly blow away the classloader
>> or B) have hibernate be redeployable.  One option is to place all the
>> Hibernate related classes inside Tomcat's shared Classloader.  This
>> might reduce the amount of times I need to restart.
>>
>> Seth
>>
>>
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