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Date: Thu, 23 Aug 2012 20:23:42 +1100 (NCT)
From: "Hadoop QA (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HADOOP-8632) Configuration leaking
 class-loaders
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    [ https://issues.apache.org/jira/browse/HADOOP-8632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13440172#comment-13440172 ] 

Hadoop QA commented on HADOOP-8632:
-----------------------------------

+1 overall.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12542100/HADOOP-8632-trunk-no-tabs.patch
  against trunk revision .

    +1 @author.  The patch does not contain any @author tags.

    +1 tests included.  The patch appears to include 1 new or modified test files.

    +1 javac.  The applied patch does not increase the total number of javac compiler warnings.

    +1 javadoc.  The javadoc tool did not generate any warning messages.

    +1 eclipse:eclipse.  The patch built with eclipse:eclipse.

    +1 findbugs.  The patch does not introduce any new Findbugs (version 1.3.9) warnings.

    +1 release audit.  The applied patch does not increase the total number of release audit warnings.

    +1 core tests.  The patch passed unit tests in hadoop-common-project/hadoop-common.

    +1 contrib tests.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-HADOOP-Build/1351//testReport/
Console output: https://builds.apache.org/job/PreCommit-HADOOP-Build/1351//console

This message is automatically generated.
                
> Configuration leaking class-loaders
> -----------------------------------
>
>                 Key: HADOOP-8632
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8632
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: conf
>    Affects Versions: 2.0.0-alpha
>            Reporter: Costin Leau
>         Attachments: 0001-wrapping-classes-with-WeakRefs-in-CLASS_CACHE.patch, HADOOP-8632.patch, HADOOP-8632-trunk-no-tabs.patch, HADOOP-8632-trunk.patch
>
>
> The newly introduced CACHE_CLASSES leaks class loaders causing associated classes to not be reclaimed.
> One solution is to remove the cache itself since each class loader implementation caches the classes it loads automatically and preventing an exception from being raised is just a micro-optimization that, as one can tell, causes bugs instead of improving anything.
> In fact, I would argue in a highly-concurrent environment, the weakhashmap synchronization/lookup probably costs more then creating the exception itself.
> Another is to prevent the leak from occurring, by inserting the loadedclass into the WeakHashMap wrapped in a WeakReference. Otherwise the class has a strong reference to its classloader (the key) meaning neither gets GC'ed.
> And since the cache_class is static, even if the originating Configuration instance gets GC'ed, its classloader won't.

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