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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: RFC: Prototype for a user threading library in Ada
Date: Thu, 23 Jun 2016 10:39:19 +0200
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Date: 2016-06-23T10:39:19+02:00
List-Id: <comp.lang.ada>

On 23/06/2016 03:42, Randy Brukardt wrote:

> I'd like to understand better the motivations for these features, so if you
> (or anyone else) wants to try to explain them to me, feel free.

The motivation is a two-liner. Let you have some consumer of data:

    procedure Write (Buffer : String; Last : out Integer);

It may take less than the whole string when called, but will take more 
data later. So, the parameter Last. Now you want to write a program in a 
*normal* way:

    Write ("This");
    Write ("That");

That's it.

This applies to all kinds of asynchronous communication and naturally to 
all kinds of parallel and distributed programming.

Ada tasks + blocking exchange are far too heavy-weight for many 
applications. Consider a server handling 1K connections as an example or 
a tiny embedded board running HTTP server, MQTT server, MODBUS client + 
dozens of other protocols etc.

Protected objects + non-blocking exchange are OK, but you will have to 
design your program standing on your head = saving the state between 
portions of data, running a complicated state machine. This is not 
scalable and unmaintainable.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de