2011/3/5 Jörg W Mittag <JoergWMittag+Ruby / googlemail.com>:
> (Interestingly, I haven't seen any implementations with concurrent
> green threads, which IMO is the best kind of threads. Rubinius
> originally planned to do concurrent green threads, but they never did.
> They started off with serialized green threads, then switched to
> serialized native threads and are currently in the process of
> switching to concurrent native threads.)

Some JVMs started out with M:N threading (which I think is what you
mean by concurrent green threads, i.e. M green threads mapped to N
native threads, so you can get concurrency but also lightweight
threading), but as far as I know they all abandoned it due to the
overhead of managing both concurrency and lightweight thread contexts.

If there are any green-threaded JVMs out there, it's likely they're
too slow to be useful; native JIT is hard to implement atop green
threads, so green-threaded JVMs in the past were mostly interpreted.

- Charlie