Re: Finalization of library level tasks

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

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