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NNTP-Posting-Date: Tue, 16 Aug 2011 11:25:22 -0500
Date: Tue, 16 Aug 2011 09:25:20 -0700
From: Patricia Shanahan <pats@acm.org>
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Subject: Re: Singleton Pattern
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On 8/16/2011 6:57 AM, Peter Duniho wrote:
...
> Or looked at another way: if someone has messed up the class design such
> that a singleton class is used even though the singleton instance is
> never actually needed, I'm not sure I trust that person to correctly
> implement even the basic explicit singleton initialization
> synchronization code. Even in that case, better to suffer the potential
> performance hit than to allow them to try to get the explicit
> initialization right.
...

I'm not convinced the method synchronization approach is bad from a
performance point of view. I've never seen a getInstance method as a
heavy hitter in a profile. I suspect that almost always the
synchronization will be uncontended.

After all, the method is non-trivial only once per class loader that
loads the class. The rest of the time it is one memory access and one
conditional branch. If the method is being called frequently, the memory
access hits in cache. From the second call on, the conditional branch
always goes the same way, so the processor should predict it correctly
after a few calls, making it very fast.

I do think the static final approach is even simpler.

Patricia