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From "Niall Pemberton (JIRA)" <j...@apache.org>
Subject [jira] Created: (BEANUTILS-291) Circular Reference on WeakHashMap
Date Tue, 07 Aug 2007 00:33:59 GMT
Circular Reference on WeakHashMap
---------------------------------

                 Key: BEANUTILS-291
                 URL: https://issues.apache.org/jira/browse/BEANUTILS-291
             Project: Commons BeanUtils
          Issue Type: Bug
          Components: Bean / Property Utils
    Affects Versions: 1.8.0-BETA
            Reporter: Niall Pemberton
             Fix For: 1.8.0


Clebert Suconic wrote on the dev@commons list  ....
(see http://tinyurl.com/2a9gan)

I have been investigating WeakHashMaps on BeanUtils 1.8 as part of a investigation on this:

http://jira.jboss.com/jira/browse/JBAS-2299

(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)


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 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.

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.


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