[jbosscache-dev] Fwd: Immutables.immutableSetCopy

[Brian Stansberry]

This didn't seem to go through; apologies for spam if it did.

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Date: Wed, 19 Aug 2009 17:16:31 -0500
From: Brian Stansberry <brian.stansberry at redhat.com>
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This method looks quite inefficient for its actual usage.

A look in the IDE shows its used by UnversionedNode.getChildrenNames()
and getKeysDirect(). Those pass either a ConcurrentHashMap$KeySet, a
FastCopyHashMap$KeySet, Collections$EmptySet or
Collections$SingletonSet.  The attempted optimizations (some of which
involve reflection) in immutableSetCopy can handle non of those and
eventually the HashSet copy constructor gets called.

A profiling run showed 22 invocations of UnversionedNode.getKeysDirect()
took 3,804 microseconds, of which 3,563 was in immutableSetCopy.  789 of
that was in the new HashSet(toCopy) call; the rest was basically wasted.

Any reason I shouldn't just turn this into a new HashSet(toCopy) call?

-- 
Brian Stansberry
Lead, AS Clustering
JBoss by Red Hat