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From "Niall Pemberton" <niall.pember...@gmail.com>
Subject Fwd: Circular Reference on WeakHashMap
Date Tue, 07 Aug 2007 01:37:52 GMT
Woops, should have gone to dev@ list

---------- Forwarded message ----------
From: Niall Pemberton <niall.pemberton@gmail.com>
Date: Aug 7, 2007 2:36 AM
Subject: Re: Circular Reference on WeakHashMap
To: Clebert Suconic <csuconic@redhat.com>


On 8/7/07, Clebert Suconic <csuconic@redhat.com> wrote:
> The solution seems simpler than I thought though...
>
> After looking at the report again...
> org.apache.commons.beanutils.converters.ClassConverter@22616909
>
> ClassConverter  probably has a reference to Class... I thought this was
> a reflection object.
>
> It should be WeakReference<Class>.

Yes it does (thru' AbstractConveter which it extends) - I can remove
that reference completely by just making the getDefaultType() method
abstract and having each implementation implement it.

> And... inspect your code for any other reflection usages.

OK when I get back I was going to have a play with JVMTIInterface - looks good.

Niall

> Niall Pemberton wrote:
> > On 8/6/07, Clebert Suconic <csuconic@redhat.com> wrote:
> >> I have been investigating WeakHashMaps on BeanUtils 1.8 as part of a
> >> investigation on this:
> >>
> >> http://jira.jboss.com/jira/browse/JBAS-2299
> >
> > Thanks for getting back to us so quickly.
> >
> >> (Which is not actually an issue with JBAS, but an issue when using
> >> BeanUtils as part of the classPath).
> >>
> >> There is a circular reference on the WeakHashMap, The WeakHashMap will
> >> have the ClassLoader as the key, and it will have a reference back to
> >> the Key from one of the Reflection objects. This doesn't work! (Please..
> >> no discussions about this point.. if you don't believe me, do some
> >> testing with simple stuff before discussing this and come back to me
> >> only after that)
> >
> > OK I will.
> >
> >> org.jboss.web.tomcat.service.WebAppClassLoader@16334564
> >> !--- sun.reflect.DelegatingClassLoader@27651708
> >> !--- !--- class sun.reflect.GeneratedConstructorAccessor38
> >> !--- !--- !--- [Ljava.lang.Object;@10800875
> >> !--- !--- !--- !--- java.util.Vector@838806
> >> !--- !--- !--- !--- !--- sun.reflect.DelegatingClassLoader@27651708
> >> !--- !--- !--- !--- !--- !--- class
> >> sun.reflect.GeneratedConstructorAccessor38
> >> !--- !--- !--- !--- !--- !--- !--- class java.lang.Class
> >> !--- !--- !--- !--- !--- !--- !--- !---
> >> org.apache.commons.beanutils.converters.ClassConverter@22616909
> >> !--- !--- !--- !--- !--- !--- !--- !--- !---
> >> org.apache.commons.beanutils.converters.ArrayConverter@18888821
> >> !--- !--- !--- !--- !--- !--- !--- !--- !--- !---
> >> org.apache.commons.beanutils.converters.ConverterFacade@13619754
> >> !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !---
> >> java.util.HashMap$Entry@32434103
> >> !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !---
> >> [Ljava.util.HashMap$Entry;@28236766
> >> !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !---
> >> java.util.HashMap@14997495
> >> !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !---
> >> org.apache.commons.beanutils.ConvertUtilsBean@2016953
> >> !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !--- !---
> >> !--- org.apache.commons.beanutils.BeanUtilsBean@30487951
> >> !---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!---
> >> FieldReference private java.lang.Object
> >> java.util.WeakHashMap$Entry.value=java.util.WeakHashMap$Entry@23775534
> >> Detail
> >
> > I'm not familiar with JBoss's JVMTIInterface or its output - and it
> > seems to be somewhat messed up in posting here - so I've (hopefully)
> > cleaned it up and re-posted in a Jira ticket I've opened for this
> > here:
> >
> > https://issues.apache.org/jira/browse/BEANUTILS-291
> >
> >> I don't know if I'm preaching to the choir, but just in case this is new
> >> information to someone... you should aways keep Reflection referenced as
> >> SoftReferences (if you really have to). Reflection is aways a new object
> >> so a WeakReference is too weak.
> >
> > Preach away - I have no great knowledge of this stuff.
> >
> >> On JBossSerialization I have solved this using an interesting way. I
> >> called it PersistentReference. I'm using SoftReferences, and keeping the
> >> information to recreate it case the SoftReference is cleared:
> >>
> >> http://fisheye.jboss.org/browse/JBoss/jboss-serialization/src/org/jboss/serial/references/PersistentReference.java?r=1.3
> >>
> >>
> >> And also... you guys should write a testcase to validate if the Caching
> >> is being cleared. (I don't know if you have one).
> >>
> >> http://anonsvn.jboss.org/repos/jbossserialization/trunk/tests/org/jboss/serial/memory/MemoryLeakTestCase.java
> >>
> >> You don't need to use the jboss-profiler API for this.. just create a
> >> WeakReference to a new ClassLoader, and validate if it was released at
> >> the end after some exercizing some code on this caching. You will
> >> probably need to fill your memory almost to 100% on the test as
> >> SoftReference are only gone when the memory is low.
> >
> > Unfortunately I'm away on holiday soon for 3 weeks (12th August to 2nd
> > September) - so unless someone else picks this up - ii don't have time
> > to look at this until after that. Do you mind if we move the
> > discussion over to that Jira ticket I opened though?
> >
> > Niall
> >
> >> Clebert Suconic
>
>

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