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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Sharing a socket connection
Date: Tue, 31 Jul 2012 12:28:27 +0200
Organization: cbb software GmbH
Message-ID: <16x1nvmt3gznc$.15s7zskookawr$.dlg@40tude.net>
References: <87hasofgwa.fsf@adaheads.sparre-andersen.dk>
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Date: 2012-07-31T12:28:27+02:00
List-Id: <comp.lang.ada>

On Tue, 31 Jul 2012 10:56:21 +0200, Jacob Sparre Andersen wrote:

> We are working on a system where a number of Ada tasks are going to
> share a single socket connection to a server [1].
> 
> The socket connection is bidirectional with requests sent from a client
> followed by corresponding responses from the server.  Each client should
> only get responses to its own requests.

This sort of multiplexing will be extremely slow. Basically you block
communication until server respond.

> Our current approach is to encapsulate the socket in a package, and use
> a mutex [2] to lock the socket during an entire
> send-request-get-response operation.
> 
> Greetings,
> 
> Jacob
> 
> [1] The rationale for this is that the individual tasks only are
>     expected to use the server sporadically, and that letting each task
>     have its own connection may use too many limited resources on the
>     server.
> 
> [2] Do the standard libraries include a mutex (I have a vague
>     recollection of having seen one, but can't find it), or should we
>     just implement it ourselves (or use the one in "Simple components
>     for Ada").

If you look at the implementation there, it is quite simple.

My primary concern would making it full duplex multiplexed. Because
half-duplex communication is really one of the major performance killers.

I would consider a request [protected] object queued to a dedicated task
doing I/O. The object would be waitable for the task that queued it. Which
is basically how OS drivers work.

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