[cpp-threads] modes

[Doug Lea]

Alexander (and Peter?), how about you humor me and, for each mode you
like not in minimal list, present a case that arguably meets the
criteria ...

> only if there are compelling use cases for modes needed in
> constructions that:
>     1. arise in common or important situations,
>     2. can't be expressed without special modes,
>     3. will remain inefficient even when compilers start
>        routinely optimizing wrt memory barriers etc in compliant code,
>     4. will remain useful even as hardware vendors continue
>        with their (very) recent trends to make most barriers etc cheaper
>        (and thus less worthwhile to evade in corner cases).
> 

... so we can discuss whether they pass some consensus threshold that
we must establish.

Thanks!

-Doug