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From: Dmitry A.Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Overriding discriminants perplexes GNAT 3.14p
Date: Sat, 21 Sep 2002 00:06:27 +0200
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Adam Beneschan wrote:

> Dmitry A.Kazakov <mailbox@dmitry-kazakov.de> wrote in message
> news:<amc58u$4ebgo$1@ID-77047.news.dfncis.de>...
> 
>> 2. Circular requeue hangs at run-time under Linux:
>> 
>> package Objects is
>>    protected Object1 is
>>       entry Point1;
>>       entry Point2;
>>    end Object1;
>>    protected Object2 is
>>       entry Point1;
>>    end Object2;
>> end Objects;
>> ------------
>> package body Objects is
>>    protected body Object1 is
>>       entry Point1 when True is
>>       begin
>>          requeue Object2.Point1;
>>       end Point1;
>>       entry Point2 when True is
>>       begin
>>          null;
>>       end Point2;
>>    end Object1;
>>    protected body Object2 is
>>       entry Point1 when True is
>>       begin
>>          requeue Object1.Point2;
>>       end Point1;
>>    end Object2;
>> end Objects;
>> ------------
>> with Ada.Text_IO;  use Ada.Text_IO;
>> with Objects;
>> 
>> procedure Test is
>> begin
>>    Objects.Object1.Point1;
>>    Put_Line ("That's OK");
>> end Test;
> 
> I think GNAT's behavior is legitimate here.  Protected entry calls and
> external requeues start new "protected actions" on the target
> protected object (9.5.3(8), 9.5.4(11)).  Thus, when
> Objects.Object1.Point1 is called, a new protected action is started on
> Object1.  When this requeues to Object2.Point1, a new protected action
> is started on Object2; however, the protected action on Object1 does
> not complete (AI95-00148). 

Really? 9.5.4(10) says explicitly (for an internal requeue) that the 
ongoing action continues., but following it 9.5.4(11) keeps silence about 
that. From which I would assume that the ongoing action is replaced by a 
new one. If not, then a task may simultaneously perform an unlimited number 
of protected actions! I see no sense in that, and moreover, it would make 
external requeues almost useless.

-- 
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de