Thread-local storage and Performance

[dsimcha]

== Quote from Pelle Månsson (pelle.mansson at gmail.com)'s article
> dsimcha wrote:
> > Has D's builtin TLS been optimized in the past 6 months to year?  I had
> > benchmarked it awhile back when optimizing some code that I wrote and
> > discovered it was significantly slower than regular globals (the kind that are
> > now __gshared).  Now, at least on Windows, it seems that there is no
> > discernible difference and if anything, TLS is slightly faster than __gshared.
> >  What's changed?
> I was under the impression that TLS should be faster due to absence of
> synchronization.

__gshared == old-skool cowboy sharing, i.e. plain old unsynchronized globals.

Without getting into the details of my specific case, the reason I'm interested in
this is that I have some code that I want to be as fast as possible in both
single- and multithreaded environments.  Right now, it has a hack that checks
thread_needLock() and uses plain old globals for everything as long as the program
is single-threaded because that seemed faster than TLS lookups a while ago.
However, running the same benchmark again shows otherwise.