Threads vs. continuations

[Paul Rubin]

John Nagle <nagle at animats.com> writes:
>     People did things like that to hammer threading onto operating
> systems so dumb they couldn't context switch, like
> DOS, early Windows, and MacOS through 7.  Nobody does that
> any more.

I see stuff heading more the other way; here's a description of a test
of Erlang with 20 million (userspace) threads:

http://groups.google.com/group/comp.lang.functional/msg/33b7a62afb727a4f

I don't know of any OS's that can handle that many threads.
Lightweight userspace threads also makes it sane to do things like
make GUI's with a separate thread per widget, and in general to
handle large numbers of concurrent tasks without the large memory
footprint and context switch overhead of kernel level threads.