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From Clebert Suconic <csuco...@redhat.com>
Subject Re: Circular Reference on WeakHashMap
Date Tue, 07 Aug 2007 01:26:13 GMT
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>.


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


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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