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Date: Mon, 16 Apr 2018 02:19:55 -0700 (PDT)
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Subject: Re: Finalization of library level tasks
From: AdaMagica <christ-usch.grein@t-online.de>
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Xref: reader02.eternal-september.org comp.lang.ada:51542
Date: 2018-04-16T02:19:55-07:00
List-Id: <comp.lang.ada>

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;
> >=20
> >    procedure Finalize (X: in out T) is
> >    begin
> >      if X.Worker'Callable then
> >        X.Worker.Quit;
> >      end if;
> >    end Finalize;
>=20
> This task will hang in the select statement.
>=20
> Terminate alternative is almost always useless because it cannot be=20
> mixed with "else" or "delay".

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

Terminate is designed for passive tasks (let's call them thus), which becom=
e 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=20
> task if its completion has been requested your solution would work.=20
> Terminate should have been a normal predefined entry:
>=20
>     task body T is
>     begin
>        select
>           accept T'Terminate;
>           exit;
>        or ...

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