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-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!news4.google.com!proxad.net!feeder1-2.proxad.net!194.25.134.126.MISMATCH!newsfeed01.sul.t-online.de!t-online.de!newsfeed.arcor.de!newsspool4.arcor-online.net!news.arcor.de.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: task model
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: 
 <04458a0b-1e58-478b-a2f0-c47226f840ac@f16g2000yqm.googlegroups.com>
 <c086cde9-96bf-47be-b56f-3793255788f2@a21g2000yqc.googlegroups.com>
 <6b6bd661-06b0-4ef6-8d48-0ef97d55fdd4@f20g2000prn.googlegroups.com>
 <nahsigbubftd.6s9bknzww2a4$.dlg@40tude.net>
 <m2d44na0xd.fsf@hal.futureapps.de> <hbaj1q$m4l$1@news.tornevall.net>
 <m2hbty8eer.fsf@hal.futureapps.de>
Date: Sat, 17 Oct 2009 14:18:54 +0200
Message-ID: <xqeaoehzajm.jehv9torj000$.dlg@40tude.net>
NNTP-Posting-Date: 17 Oct 2009 14:18:53 CEST
NNTP-Posting-Host: ac75d47f.newsspool2.arcor-online.net
X-Trace: 
 DXC=a7T1SmYFW1D78PK[oJ2ng@A9EHlD;3YcB4Fo<]lROoRA8kF<OcfhCOKd2054@dQ6SN[6LHn;2LCVN[<mhadbfdUK@KEe^3jK[UCM\]2ZcCIZhL
X-Complaints-To: usenet-abuse@arcor.de
Xref: g2news2.google.com comp.lang.ada:8715
Date: 2009-10-17T14:18:53+02:00
List-Id: <comp.lang.ada>

On Sat, 17 Oct 2009 13:10:04 +0200, Georg Bauhaus wrote:

> "Jeffrey R. Carter" <spam.jrcarter.not@spam.acm.org> writes:
> 
>> Georg Bauhaus wrote:
>>
>> What's the point of re-raising? Exceptions don't propagate from tasks.
> 
> Uhm, I forgot to mention that a handler at some nesting level
> might be reporting, permitting more accurate diagnostic messages.
> It could then decide there is or is not a possible rescue,
> and accordingly re-raise, for example.

The problem is that there is no nesting of tasks in terms of control flow.
There is a parent child relation, but it is no nesting.

If an exception is propagated out of a task, the parent task is doing its
things asynchronously to the child. In order to propagate an exception in
the parent you have only two options:

1. an asynchronous transfer of control = in effect aborting/interrupting
the parent;
2. to synchronize with the parent making a rendezvous with it.

Neither looks much promising.

More generally speaking in Ada tasks are objects. As an object a failed
task may complain no earlier than upon its finalization if no other
contacts (rendezvous) happen. This is too late in all senses.

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