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=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: a07f3367d7,385c146dd3112519
X-Google-Attributes: gida07f3367d7,public,usenet
X-Google-NewGroupId: yes
X-Google-Language: ENGLISH,UTF8
Path: 
 g2news1.google.com!news1.google.com!news4.google.com!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From: "Alex R. Mosteo" <alejandro@mosteo.com>
Newsgroups: comp.lang.ada
Subject: Re: Private or public task ?
Followup-To: comp.lang.ada
Date: Tue, 09 Feb 2010 15:44:17 +0100
Message-ID: <7tdap6F251U1@mid.individual.net>
References: 
 <a35584dd-8693-484d-918d-758940dccfe8@d37g2000yqa.googlegroups.com>
 <hki3p7$bas$1@tornado.tornevall.net>
 <38a0a3f9-b4a0-48f3-98c9-63b03fe03aca@q4g2000yqm.googlegroups.com>
 <e714f043-9fed-4e2b-b3d2-180b0364f0cf@d27g2000yqn.googlegroups.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8Bit
X-Trace: individual.net /9uSBfKGvo/rSVoaQ7G/5Q6WF8KNgOweB0mv1Lpz/CWTNSc8s=
Cancel-Lock: sha1:uRpwNvaU3lDcYmG38QeAiMmJcLs=
User-Agent: KNode/4.4 rc2
Xref: g2news1.google.com comp.lang.ada:9036
Date: 2010-02-09T15:44:17+01:00
List-Id: <comp.lang.ada>

Maciej Sobczak wrote:

> On 5 Lut, 22:53, Hibou57 (Yannick Duchêne) <yannick_duch...@yahoo.fr>
> wrote:
> 
>> I did not ever suspected such a requirement. Transitive blocking is
>> not allowed ?
> 
> As far as I understand, there is a careful wording around this subject
> so that formally speaking protected operations (except for entries)
> are not themselves "blocking". So, for example, you can call protected
> operations from other protected operations.

And this makes sense: if you don't allow anything blocking inside a 
protected procedure, it follows that the procedure is itself non-blocking :)

Entries, on the other hand, are blocking... because you don't know if you'll 
be blocked on the entry conditional. This is true even for non-conditional 
entries, I think, because of possible requeues.

Alex.

> The operations that are considered to be blocking in this context are
> delay statements, entry calls, select statements and... I/O
> operations. These cannot be called from protected operations.
> 
> (I'm sure somebody will correct me if I'm off tracks)
> 
>> So, if blocking operation are not allowed from a protected type,
>> clients of a given operation have to know it weither or not it's
>> potentially blocking,
> 
> That would be nice, yes. But be careful, this approach might blow up
> the language. What about exception specifications? And so on.
> 
> But: see RavenSPARK.
> 
> The problem with blocking in particular is that there is no way to
> verify whether imported subprograms (from C libraries, for example)
> are blocking. You can import I/O operations from C libraries and there
> is no way to verify what they do.
> 
> --
> Maciej Sobczak * www.msobczak.com * www.inspirel.com
> 
> Database Access Library for Ada: www.inspirel.com/soci-ada