Side note: the alternative, of course, is to just use the atomic bit
operations. They aren't generally much (if at all) faster than locking +
doing the operation + unlocking, but they can avoid lock contention, so
if you do a lot of bit ops that need no other locking than the setting and
clearing (possibly with testing), then they are the right choice.
For signals, we obviously need other locking, so the atomic bit ops are a
waste of time (doing *both* locking for other reasons *and* atomic bitops
is obviously much slower than either).
Linus
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