[BEANUTILS-291] Circular Reference on WeakHashMap

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.8.0-BETA
• Fix Version/s: 1.8.0
• Component/s: Bean / Property Utils
• Assignee: Niall Pemberton
• Reporter: Niall Pemberton
• Created: 07/Aug/07 00:32
• Updated: 08/Oct/09 21:38
• Resolved: 19/Aug/08 16:58

Description

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
Unable to render embedded object: File (--- !--- !--- !--- !--- !--- !--- !--- !-- -) not found.--- !--- !--- !--- !--- !--- !---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.

Issue Links

• relates to: BEANUTILS-366 MemoryLeakTestCase fails for IBM JDK 1.6