I think that there may be a problem of kind here.

Are winding continuations a la R5RS *compatible* with threads?  Do
they belong in the same langauge?

To me it looks like if you have non-blocking I/O and call/cc with
winding continuations, you don't need threads.  And if you want
dynamic state maintained for safety by winding continuations, you
can't have threads of the kind you're talking about without some
fundamentally new state-maintenance operations that can handle
arbitrary multiple points of program execution simultaneously.

I'm aware of the vast flamage which has occurred on the topic of
winding continuations in general.  And I don't want to touch off a
flamefest here.  But it seems to me that threading and any kind of
protected call/cc are probably fundamentally opposed ideas and that
you can't have both in the same program without a flawed design.

				Bear