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From Craig L Russell <Craig.Russ...@Sun.COM>
Subject Re: classes registered in JDOImplHelper unloaded
Date Mon, 06 Mar 2006 16:45:07 GMT
Hi Erik,

The JDOImplHelper cannot use soft references to registered classes  
because it wasn't clear what would happen if the class is garbage  
collected and then used again. We wanted to make sure that the  
JDOImplHelper would always have the metadata for the class.

To solve this problem, we added the methods unregisterClass and  
unregisterClasses that allow the JDO implementation to explicitly  
remove the classes from the JDOImplHelper.  It's not automatic (the  
implementation needs to have some kind of life cycle manager) but it  
seems to work in practice (e.g. in application servers).

We can open this up if people with strong knowledge of the behavior  
of the class loader can take a look at it.

Craig

On Mar 6, 2006, at 8:25 AM, Erik Bengtson wrote:

> Let me rewrite in English ;)
>
> Hi,
>
> If applications using short lived classloaders register PC classes,  
> and later on
> these classloaders are released. Classes should be GC together with  
> the
> classloaders, but the JDOImplHelper is holding strong references to  
> these
> classes.
>
> What is the strategy to take to avoid a memory leak in JDOImplHelper?
>
> Regards,
>
> Quoting Erik Bengtson <erik@jpox.org>:
>
>>
>>
>> Hi,
>>
>> What happens if the classes registered in a JDOImplHelper are  
>> unloaded or if
>> an
>> attempt to GC the classloader?
>>
>> Later on the same class loaded by a second classloader, third,  
>> forth and so
>> on?
>>
>> Is there a memory leak here since the classloader will not be  
>> garbage collect
>> the classes as we have a strong references to the classes?
>>
>> Regards,
>>
>> Erik Bengtson
>>
>
>
>

Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:Craig.Russell@sun.com
P.S. A good JDO? O, Gasp!


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