[m-users.] mmc option parallel

[Peter Schachte]

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On 16/03/2015 10:23 am, Paul Bone wrote:
> I believe that the long term solution is to make a clear separation between options and grade
components. And possibly to abstract away grades altogether. A user
should be able to say "I want parallelism" and get it, as you suggest,
by the system choosing the best parallel grade available. Thanks.

Grades are something the Mercury implementors are interested in, and
users are not.  The better you can hide them from users, the better.  If
Mercury had a pragma to allow a file to specify that it needs some grade
component, most users would not need to use it or even know about it. 
Some libraries would specify that they need a trail, or threads, or
stack segments, etc.  It would be up to the build system to piece
together the grade components needed by the (recursive dependencies of)
the application source files, and validate that they don't conflict.  It
should also keep track of what grade the current object files were built
with and rebuild if the grade changes (or perhaps generate each grade in
a different subdirectory to keep them from interfering with one
another).  There should also be some compiler switches for things like
debugging, stack segments, or leaving out the garbage collector, but the
user would not need to be aware they relate to grades.  This should
allow all but the most advanced users to remain ignorant of grades.

Regarding the time taken to build the library in different grades, how
about having the compiler create a directory somewhere under the user's
home directory holding (caching) the library files built in the grades
that have been needed in the past.  Then it would not be necessary to
build any libraries at install time other than those used in the
compiler itself.  This would waste space on a multiuser system where
many people use Mercury, since some generated files would be stored
under several people's home directories, but space is pretty cheap these
days, and most people have single-user computers anyway.  There would
also be space and time *savings* since only library files that have been
used would be built, and only in the grades they've actually been used in.


- -- 
Peter Schachte            History teaches us that men and nations behave
University of Melbourne   wisely once they have exhausted all other
schachte at unimelb.edu.au   alternatives. -- Abba Eban
Phone: +61 3 8344 1338
people.eng.unimelb.edu.au/schachte/
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