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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Problem with task component
Date: Wed, 19 Sep 2012 23:11:20 +0200
Organization: cbb software GmbH
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Date: 2012-09-19T23:11:20+02:00
List-Id: <comp.lang.ada>

On Wed, 19 Sep 2012 21:40:40 +0100, Simon Wright wrote:

> Also, it seems to me that if I don't use pointers I'm going to have
> trouble finalizing the object: the contained task is sitting there and
> prevents leaving the scope in which its containing object is declared,
> so the containing object doesn't get finalized and there's no
> opportunity for Finalize to tell the task to stop.

You need an open terminate-alternative ("or terminate;") when the object
containing the task component is about to finalize.

The usual problem is that the terminate-alternative does not live together
with the delay-alternative and/or else-part, which makes it quite a
challenge to implement something like a typical "driver" component task:

task body Driver is
begin
   loop
      do I/O;
      exit/terminate when parent dies;
   end loop;
end Driver;

If the I/O subsystem calls to the task upon I/O completion, you could try
something like this:

task body Driver is
begin
   loop
      Start_IO (Self);
      select
         accept Completed (...);
         ... -- Process the data
      or accept Canceled;
         ... -- I/O was canceled
      or accept Error (...);
         ... -- I/O error
      or terminate; -- Still have troubles killing all outstanding requests
      end select;    -- which may refer to the driver task, that is gone
   end loop;         -- by now
end Driver;

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