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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Timeouts in Ada
Date: Fri, 25 Jul 2014 18:34:40 +0200
Organization: cbb software GmbH
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Date: 2014-07-25T18:34:40+02:00
List-Id: <comp.lang.ada>

On Fri, 25 Jul 2014 02:11:29 -0700 (PDT), AdaMagica wrote:

> On Thursday, July 24, 2014 5:37:39 PM UTC+2, Robert A Duff wrote:
> 
> But this is not the same as
> 
>>    select
>>      call_1(params);
>>    or
>>      call_2(params);
>>    or
>>      delay 10;
>>    end select;

BTW, there could be any combination of counters:

   select
      call_1 (params);
   and
      call_2 (params);
   or
      delay 10;
   end select;

Calls or makes rendezvous with two entries indivisibly.

A use case is prevention of deadlocks with mutexes:

Task 1:

   select -- Acquire both or none
      Resource_1.Seize;
   and
      Resource_2.Seize;
   end select;

Task 2:

   select
      Resource_2.Seize;
   and
      Resource_1.Seize;
   end select;

is safe, while

Task 1:

    Resource_1.Seize;
    Resource_2.Seize;

Task 2:

   Resource_2.Seize;
   Resource_1.Seize;

is unsafe.

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