On a related note, the Plan 9 system call rfork() gives a system call by which you can create new processes or lightweight processes(threads) with a single system call, deciding on what resources are to be shared between the new processes. There are no 2 discrete entities called processes and threads, just processes !

"In Plan 9, fork is not a system call, but a special version of the true system call, rfork (resource fork) which has an argument consisting of a bit vector that defines how the various resources belonging to the parent will be transferred to the child. Rather than having processes and threads as two distinct things in the system, then, Plan 9 provides a general process-creation primitive that permits the creation of processes of all weights." - Rob Pike.

You can read more about it here - http://groups.google.com/group/comp.os.research/browse_threa...