From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-0.3 required=5.0 tests=BAYES_00,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Thread: 103376,94e5dd5646e21259
X-Google-Attributes: gid103376,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news3.google.com!feeder1-2.proxad.net!proxad.net!feeder2-2.proxad.net!newsfeed.arcor.de!newsspool1.arcor-online.net!news.arcor.de.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Interfacing to C: multithreaded callbacks
Newsgroups: comp.lang.ada
User-Agent: 40tude_Dialog/2.0.15.1
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Reply-To: mailbox@dmitry-kazakov.de
Organization: cbb software GmbH
References: <1181678190.757347.67290@x35g2000prf.googlegroups.com>
Date: Wed, 13 Jun 2007 10:11:30 +0200
Message-ID: <m8lrp9shht63$.w8hlpj4jf0ve$.dlg@40tude.net>
NNTP-Posting-Date: 13 Jun 2007 10:08:52 CEST
NNTP-Posting-Host: 6cb68b77.newsspool2.arcor-online.net
X-Trace: 
 DXC=XWb[TE[Y[b7L2C_`koXfC5A9EHlD;3Yc24Fo<]lROoR18kF<OcfhCO;9cnm?ME5JI8[6LHn;2LCV>7enW;^6ZC`4IXm65S@:3>?`jPc@>:31A8
X-Complaints-To: usenet-abuse@arcor.de
Xref: g2news1.google.com comp.lang.ada:16177
Date: 2007-06-13T10:08:52+02:00
List-Id: <comp.lang.ada>

On Tue, 12 Jun 2007 12:56:30 -0700, Maciej Sobczak wrote:

> The problem is when the C library creates additional threads and calls
> the client back in the context of those threads. ARM says nothing (?)
> about the relaion between Ada tasks and system threads. If the
> relation is 1:1 (ie. tasks are implemented as system threads), then
> the whole scheme might work just fine, provided that there is no task-
> specific data that Ada runtime expects and will not find. On the other
> hand, if the relation between tasks and threads is not 1:1, we will
> just enjoy undefined behavior.

Yes, when Ada tasks aren't mapped onto system threads, then system calls
potentially might block all Ada tasks. This includes whatever POSIX layer.

> Is there any water-proof implementation pattern for such problems?
> Consider both the general case and then GNAT as the target Ada
> compiler on POSIX systems.

You can marshal messages from C callbacks. With busy waiting and one
publisher - one subscriber, you don't need anything but shared memory to
implement that.

However, when talking about  POSIX targets, I would assume Ada tasks being
POSIX threads.

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