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From "Robert Joseph Evans (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8632) Configuration leaking class-loaders
Date Wed, 15 Aug 2012 16:23:38 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13435253#comment-13435253
] 

Robert Joseph Evans commented on HADOOP-8632:
---------------------------------------------

When I try to apply the patch to trunk I get
{noformat}
$ patch -p 0 < HADOOP-8632.patch 
patching file hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java
Hunk #3 succeeded at 1532 (offset 55 lines).
patching file hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/conf/TestConfiguration.java
Hunk #2 FAILED at 1044.
1 out of 2 hunks FAILED -- saving rejects to file hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/conf/TestConfiguration.java.rej
{noformat}

You may want to try upmerging the patch to trunk.
                
> 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
>
>
> 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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