The compiled-ness or not of the code is almost irrelevant to the
lightweightedness of the thread system.
The essence of lightweight threads is that it gives you much of the
usefulness of a separate process without much of the setup cost. Thus a
Smalltalk Proces is actually a rather good example of what most people
would mean by a lightwieght thread - it costs almost nothing to setup and
operate. A Unix process fork on the other hand is quite heavy weight since
it involves basically copying the entire process space of the spawner
process, and then full scale process context switches in use. Various
optimisations have been made over time like memory copy-on-write, but it
still costs quite a bit.
The context swapping cost might possibly be better with very optimised
compiled code, but don't forget that the context switching code in
Smalltalk is a primitive that should be just as well compiled...

tim

-- 
Why Dogs Hate WIn95:-10)  Oh, but they WILL... with the introduction of the Microsoft Opposable Thumb.
Tim Rowledge:  rowledge at interval.com (w)  +1 (650) 842-6110 (w)
 tim at sumeru.stanford.edu (h)  <http://sumeru.stanford.edu/tim>