This is a fast, scalable chained hash table with optional auto-resizing, allowing
reads that are concurrent with reads, and reads/writes that are concurrent
with writes to separate buckets.

A hash table with these features will be necessary for the scalability
of the ongoing MTTCG work; before those changes arrive we can already
benefit from the single-threaded speedup that qht also provides.
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Message-Id: <1465412133-3029-11-git-send-email-cota@braap.org>
Signed-off-by: NRichard Henderson <rth@twiddle.net>