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    One of the themes informing these suggestions is that no one really
    knows at this point what the wins to be had from lightweight
    multiprocessing are, so one would not want to prematurely exclude
    any capabilities.

A number of large programming environments have included lightweight
processes, including Mesa, Cedar, Smalltalk, and Lisp Machines of various
sorts.  I think they would all take issue with the fact that "no one knows"
what would be the wins of lightweight processes.

Of my passing familiarity with all these, I would say that Mesa has the
most experience with lightweight processes.  Mesa systems have used them
for a large number of applications for many years:  low level device
interfaces, high level user interfaces, networking, etc.

Part of the problem with T is that it is expected to run on various
operating systems which all provide only "heavyweight" processes.  As
long as the operating system provides non-blocking versions of all its
blocking system calls and a decent timer interrupt, one could make a fairly
good approximation to lightweight processes.  But there would be much
pain in making such an approximation clean and relatively operating system
independent.  Note that one could do a decent job on Aegis and probably
VMS, but vanilla Berkeley Unix (at least 4.1) doesn't provide all the
necessary primitives.