light-weight processes in Unix

[dms at hermes.ai.mit.EDU]

We'd like to add some kind of light-weight process support to our Sun
3.2 system. What we would like to have is the ability to fork off a
procedure (not a fully linked program) that shares the full address
space of the parent process. The stack and heap for the child process
would be malloc'ed out of the parent's heap. There are, of course,
complications that would come up if both child and parent were using
shared data structures, such as the io buffers. Ignoring these (for
you could write code keeping this in mind), has anyone attempted to do
this? 

Thanks,
-Dave