PreferredClassProvider classloader cache concurrency improvement
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Key: RIVER-396
URL: https://issues.apache.org/jira/browse/RIVER-396
Project: River
Issue Type: Improvement
Components: net_jini_loader
Affects Versions: River_2.1.2
Reporter: Chris Dolan
Priority: Minor
The PreferredClassProvider.lookupLoader() method uses a single coarse lock to
synchronize its cache of ClassLoader instances. Because the creation of a
ClassLoader can be an expensive operation (including remote calls in some
special cases) this global lock can be a significant bottleneck.
Attached is a patch to refactor that code to hold only a finer grained lock
while constructing the ClassLoader in case of a cache miss. The refactor moves
the ReferenceQueue field out of any synchronized block, because that class is
already thread-safe. The refactor still holds a coarse lock while checking the
cache, but holds only a finer lock (per cache line) while checking and possibly
creating the ClassLoader.
See also RIVER-336 where an alternative version of this patch was proposed.
But a following analysis revealed concurrency problems with that patch:
http://mail-archives.apache.org/mod_mbox/river-dev/201104.mbox/browser
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