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From "Clebert Rezende Suconic (JIRA)" <j...@apache.org>
Subject [jira] Commented: (BEANUTILS-291) Circular Reference on WeakHashMap
Date Mon, 07 Apr 2008 15:33:24 GMT

    [ https://issues.apache.org/jira/browse/BEANUTILS-291?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12586430#action_12586430
] 

Clebert Rezende Suconic commented on BEANUTILS-291:
---------------------------------------------------

I see one problem on MappedPropertyDescriptor.java

There is nothing testing if mappedReadMethodRef.get()==null, then recreate it.


Reflection is an unique object on the JVM. Everything you do class.getmethod (or getField..
whatever), you get a new object.


Since this is using SoftReference, when the memory goes low, you will certainly loose the
reference to ReadMethod, but the class will still be loaded (and valid). So, on that case
you need to do a:

if (mappedReadMethodRef.get() == null)
{
     mappedReadMethod = createReferenceAgain();
}

// this is a fictitious name... just to illustrate the idea: 
public synchronized createReferenceAgain()
{
 ...
}

To correctly testcase this scenario on SoftReferences, you should get a BeanDescriptor (forcing
the creation of MappedPropertyDescriptor), force a OutOfmemoryError, and then make an operation
again.  I didn't do any tests yet but I believe you would have a NPE on that scenario.


> 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
>
>         Attachments: BEANUTILS-291-FixMemoryLeaks-v2.patch, memoryLeakTests-new.zip,
PropertyUtilsBean.java
>
>
> 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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