[cpp-threads] modes, interlude

[Doug Lea]

> But I don't think there's a very clean way to separate out the
> "acquire" barrier from a load_acquire.  I doubt you would separate it.
> The barrier is only meaningful because it's attached to the load.
> If you're allowed to move it, it's no constraint at all.  Or it
> becomes full barrier, which is much more expensive.
> 

Well, it is always decodable to have such a barrier modify
the textually subsequent load. I agree that it might be less pleasant
to use, although maybe still more pleasant than having to remember
what "hsb" and the like mean :-) In any case, I'm not particularly
advocating doing it this way.

-Doug