Re: Finalization of library level tasks

[AdaMagica <christ-usch.grein@t-online.de>]

Am Sonntag, 15. April 2018 19:40:38 UTC+2 schrieb Dmitry A. Kazakov:
> On 2018-04-15 19:17, AdaMagica wrote:
> > task body Worker_Type is
> >    begin
> >      loop
> >        select
> >          accept Quit;
> >          exit;
> >        or
> >          terminate;
> >        end select;
> >      end loop;
> >    end Worker_Type;
> > 
> >    procedure Finalize (X: in out T) is
> >    begin
> >      if X.Worker'Callable then
> >        X.Worker.Quit;
> >      end if;
> >    end Finalize;
> 
> This task will hang in the select statement.
> 
> Terminate alternative is almost always useless because it cannot be 
> mixed with "else" or "delay".

The only way to request the completion from outside a task is (if I remember correctly) an abort statement. Then you don't need terminate.

Terminate is designed for passive tasks (let's call them thus), which become active only on request, i.e. via an entry call. Thus terminate, delay and else-statement are mutually exclusive. (I'm sure you know all this well.) Terminate is called by (hm, dunno, a task supervisor) when it is clear that there are no more clients who can call any of the entries, so the task has nothing more to do. A delay or else-statement would be a contradiction.

Thus your design seems wrong if you need something like this.

> If there were a way to check within the 
> task if its completion has been requested your solution would work. 
> Terminate should have been a normal predefined entry:
> 
>     task body T is
>     begin
>        select
>           accept T'Terminate;
>           exit;
>        or ...

This would lead to a very different tasking feature - a completely different Ada you every now and then seem to propose.