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=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Finalization of library level tasks
Date: Fri, 27 Apr 2018 10:57:32 +0200
Organization: Aioe.org NNTP Server
Message-ID: <pbuols$h7u$1@gioia.aioe.org>
References: <pavkou$1go7$1@gioia.aioe.org> <pavm21$ko5$1@dont-email.me>
 <pavmla$1k1o$1@gioia.aioe.org> <pavp2a$81n$1@dont-email.me>
 <pavqa6$1qdj$1@gioia.aioe.org> <pbr405$lg5$1@franka.jacob-sparre.dk>
 <pbs4km$doq$1@gioia.aioe.org> <pbtjlf$k6q$1@franka.jacob-sparre.dk>
 <pbuk07$9mf$1@gioia.aioe.org>
 <b5efd763-f3fe-46e1-a041-76fd47b21eb3@googlegroups.com>
NNTP-Posting-Host: MyFhHs417jM9AgzRpXn7yg.user.gioia.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Complaints-To: abuse@aioe.org
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101
 Thunderbird/52.7.0
X-Notice: Filtered by postfilter v. 0.8.3
Content-Language: en-US
Xref: reader02.eternal-september.org comp.lang.ada:51745
Date: 2018-04-27T10:57:32+02:00
List-Id: <comp.lang.ada>

On 27/04/2018 10:32, AdaMagica wrote:
> Am Freitag, 27. April 2018 09:37:46 UTC+2 schrieb Dmitry A. Kazakov:
>> You *can* finalize the class of the object containing the task with the
>> task component still running:
>>
>>      type Container_Type is .. tagged ...
>>         T : Task_Type;
>>
>> The order of finalization must be:
>>
>>      Finalize Container_Type'Class;
>>      Stop T;                  -- Existing order
> 
> IIUC, you mean the task T is stopped anywhere in the middle of its work?

No, I mean that the task is awaited, e.g. to accept terminate.

What I meant is that finalization of a class object does not need to 
wait for the task to end. Therefore from the class' Finalize you could 
ask the task to stop:

    task type Task_Type is
       entry Shutdown;
    end Task_Type;

    type Container_Type is
       new Ada.Finalization.Limited_Controlled with
    record
       T : Task_Type;
    end record;

    procedure Finalize (Object : in out Container_Type'Class);
    for Container_Type'Class'Finalize use Finalize ; -- Whatever syntax

    procedure Finalize (Object : in out Container_Type'Class) is
    begin
       Object.T.Shutdown; -- You cannot do that from normal Finalize,
    end Finalize;         -- it is too late then

Presently class finalization is null. BTW, after class finalization 
dispatching calls on the class must result in an exception. It should 
have been a bounded error to dispatch from Initialize or Finalize.

One of the inconsistencies of controlled types design is that 
dispatching is allowed in Finalization <=> the class considered 
operational, but task components are not running <=> the class 
considered non-operational. Either one or another.

> Ada calls this abort. This means a lot of things may be left in an invalid state.

Yes. Task abort is almost never usable.

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