Re: Teaching Concurrency

[meissner@osf.org (Michael Meissner)]

In article <10330@june.cs.washington.edu> pattis@cs.washington.edu (Richard Pattis) writes:

| OK, so this begs the question: what is the "smallest" assignment that can
| use concurrency fruitfully. I would like to teach a bit about tasking in
| one of my classes, but I don't want students to get "wrong" ideas from the
| example I use.  Anyone out there have such an assignment? Is there some prime
| example out there of a good use of multi-tasking that is amenable to
| classroom instruction?

When I was at Data General, and we wanted to convey how to use the
operating systems (RDOS, AOS, AOS/VS, but not unix) task facility, we
would use a cut down version of the tape archiver as an example.  In
the simplest case, you want to copy a file, overlapping the I and O
portions, you would then have a producer task and a consumer task, and
n buffers to use between the two, and then go on to the various
strategys of inter-task communication and buffer management.

The full blown tape archiver was a little bit more complicated (it had
tasks which did the equivalent of opendir, readdir, and closedir, and
fstat on the files, tasks which read in the files, and an output task
which ordered things appropriate, and wrote to the tape).  It took all
of the parallelism to make most tapes stream when doing a through the
filesystem backup.

Another fun multitasking example, was to use two tasks to write an
arcade-style game with terminal graphics (one task for terminal input,
and the other task for output).

Finally, there is the example of a multi-tasked server, or transaction
processing system, but that is perhaps too complicated for a classroom
setting.

The problem with a real world examples like the above is if your
operating system does not have real tasks (threads, etc.), and merely
simulates it, you don't get any benifits from tasking, and it is
better to write the stuff single threaded.

IMHO, I believe that the normal task examples like slowsort, or what
have you are not so useful in real world programming, and may in fact
encourage bad habits.

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Michael Meissner	email: meissner@osf.org		phone: 617-621-8861
Open Software Foundation, 11 Cambridge Center, Cambridge, MA

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