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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Simp,e example for 2 tasks
Date: Mon, 22 Sep 2014 10:18:37 +0300
Organization: Tidorum Ltd
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Xref: number.nntp.dca.giganews.com comp.lang.ada:189081
Date: 2014-09-22T10:18:37+03:00
List-Id: <comp.lang.ada>

On 14-09-21 23:33 , Jeffrey Carter wrote:
> On 2014-09-21 7:31 AM, Stribor40 wrote:
>> Would anyone be able to post simple example of ada program showing 2 tasks
>> taking to each other please.  For example one task sends message to another
>> saying "hi" and second taks replying "hi back".
> 
> As others have pointed out, Ada tasking is based on synchronous communication,
> not the message queues found in other languages. This why Ada had to introduce
> the partition concept to achieve distribution, while Erlang processes distribute
> quite nicely by themselves, as the ping-pong example shows.

Hmm... I don't quite agree with that. It seems to me that rendez-vous
interaction between tasks could be implemented in a distributed system,
as long as the entry parameters can be passed by value or by copy-in
copy-out. It is the global shared variables and reference parameters
that would make a distributed approach difficult for Ada programs using
such constructs. I don't know Erlang well enough to understand if it has
some solution for that, or if it simply forbids such things.

Of course this does not alter the fact that rendez-vous is synchronous,
and that a queue has to be implemented if asynchronous communication is
needed.

For reque statements, I believe that the RTS typically packs up the
entry parameters in a record structure, like a message, which the RTS
can manipulate more easily than it could manage parameters pushed on the
stack, as for a normal call.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
      .      @       .