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From: Maciej Sobczak <see.my.homepage@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Distributed Systems Annex, data sharing between programs
Date: Sat, 9 Jun 2012 13:29:04 -0700 (PDT)
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Date: 2012-06-09T13:29:04-07:00
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On 9 Cze, 14:25, Pascal Obry <pas...@obry.net> wrote:

> > How would you do that with "calls"
> > instead of "messages"?
>
> As said in my previous message. With a queue. I have used this scheme,
> it works perfectly well.

Yes - you have just implemented a message-oriented middleware on top
of some low-level primitives known as "calls". If you have a queue,
then you have some items in there - these are exactly the messages
lifted to the level of design entities, as I've described earlier. A
push-pull queue was easy to implement on top of RPC, but what about
push-push queues? What about N:M publish-subscribe? This is where
messaging appears to be a higher-level concept.

Actually, I'm pretty convinced that RPC and messaging are
complementary and can be used to implement one another. As Dmitry
said, RPC can be achieved by send+wait on a message and as you say,
passing messages around is actually executing possibly remote calls on
some intermediary entities like queues or brokers. The question is -
when you will have to do more coding (and have more impedance
mismatch) to get from one paradigm to another.

> You can even launch new message consumers
> dynamically or stop some.

Uhm... remember the original post in this thread, by Adam? It is not
actually clear whether this is kosher or not. ;-)

--
Maciej Sobczak * http://www.msobczak.com * http://www.inspirel.com