Regarding thread local storage - isn't that typically implemented using the segment registers (on x86 at least)? So you would need to vary those between fibers

Regarding thread local storage - isn't that typically implemented using the segment registers (on x86 at least)? So you would need to vary those between fibers (instead of just between kernel threads) and your scheduler would have to explicitly save and restore them. I would guess that's not possible to do in portable C though.