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https://issues.apache.org/jira/browse/HADOOP-8632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13433375#comment-13433375
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Costin Leau commented on HADOOP-8632:
-------------------------------------
By the way, in the same vein, ReflectionUtils#CONSTRUCTOR_CACHE also leaks
classes (see HADOOP-8605 - I'm happy to fix that as well if you want).
> 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
>
>
> 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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