Re: Ada95 Streams Question

[bobduff@world.std.com (Robert A Duff)]

In article <dewar.835633090@schonberg>, Robert Dewar <dewar@cs.nyu.edu> wrote:
>Michael says:
>For the described setup it would be even more elegant to utilize an
>implementation of the distributed system annex but as this builds on the
>stream facility as well you face the same problem as mentioned above.
>If you just look at the wording of this annex the big picture is a huge
>monolithic program that is now broken into pieces (partitions)
>
>  That's not what I see reading the wording in the annex! There is no
>  huge monolithic program. What is called here a partition is what would
>  normally be called a program, and a distributed Ada "program" is in fact
>  a collection of partitions.

And the Distributed Systems annex (and chapter 10) says that you can
start and stop partitions independently of one another, while the
distributed program as a whole is running.  This doesn't sound
"monolithic" to me.  On the contrary, a distributed program is a rather
loosely connected set of relatively independent partitions.

For example, suppose you find a bug in one partition.  You can stop it,
fix the bug, recompile, and run the new version of that partition, while
the program as a whole continues to run.  (Assuming, of course, that
you've designed the other partitions to work properly in that scenario.)

>and executed as a whole on a homogenous network of computers. That is
>definitely not what I understand by distributed computing.
>
>  Well distribution may be homogenous or heterogenous. The Ada model is
>  certainly aimed at homogenous distribution, but extends fine to the
>  hetergenous case (we first demonstrated hetergenous distribution using
>  this annex nearly two years ago at Tri-Ada, running on Sun's and SGI's)

I believe the attitude of the designers of the Distributed Systems annex
was:

    1. Provide support for homogeneous distributed systems.

    2. Solving the problem of heterogeneous is beyond the scope of the
       annex, but we don't want to get in the way of supporting
       heterogeneous systems.  We hope compiler writers will address
       those issues, and who knows, maybe that support will become
       standard someday.  Thus, the DS annex should not do anything that
       *prevents* its use in heterogeneous systems.

- Bob