Costin Leau created HADOOP-8632:
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Summary: 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
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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