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From: mmh@cs.qmw.ac.uk (Matthew Huntbach)
Newsgroups: comp.parallel
Subject: Re: What sort of applications are worth parallelising?
Message-ID: <8199@hubcap.clemson.edu>
Date: 1 Mar 90 21:27:35 GMT
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In article <8117@hubcap.clemson.edu> ken%aiai.edinburgh.ac.uk@NSFnet-Relay.AC.UK (Ken Johnson) writes:
>A sub-question: What sort of application is worth parallelising with a
>parallel logic language like Strand-88 or Parlog?

A lot of the things these languages are useful for aren't
really parallel. They are just easy to express in a
pseudo-parallel style.

For real parallelism using Strand/Parlog, anything which
doesn't involve array access (which cuts out a lot of
traditional parallel applications which are often based on
array processors). The languages work fine on most
divide-and-conquer type algorithms.

However the current versions of Strand/Parlog are not much use for
OR-parallel type operations or speculative computation i.e.
the sort of thing where you know you need the result of
calculating A or B, but having the spare processors you
calculate both before you know which is required. The reason is
that usually you know that you are more likely to need say A
than B. The languages don't give you a construct which says
"calculate A, and calculate B if you have the spare processing
capacity to do so". Such a construct could easily be added to
Strand/Parlog - I've been working on it but so far haven't had
much luck persuading people it would be useful. At the moment
all you can say is "evaluate A and B in parallel" and it is up
to the underlying system which is given preference if there are
no spare processors available.

Matthew Huntbach