Re: Delayed deallocation of non-terminated task in Gnat?

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

On Tue, 30 Aug 2011 08:38:52 -0700 (PDT), Adam Beneschan wrote:

>  I'm having a bit of difficulty figuring out from
> the RM what the exact semantics of finalizing an unterminated task
> object are, but I'm pretty sure that aborting the task is not one of
> them.  (Note that this applies only to tasks without discriminants.
> If the task has discriminants, freeing it is an
> error---13.11.2(11ff).)

What is the difference? Is it an attempt to have freed tasks running
further? Or an attempt to construct a race condition, e.g. when the task
being freed has an open terminate alternative or else has been accepted a
rendezvous and now is going down? 

Considering this standard pattern:

type Object;
task type Worker (Self : not null access Object'Class) is
   entry Shut_Down;
end Worker;
type Worker_Ptr is access Worker;
type Object is new Ada.Finalization.Limited_Controlled with record
   Worker : Worker_Ptr;
end Object;
overriding procedure Finalize (This : in out Object);

Now the following is a race with a bounded error:

procedure Finalize (This : in out Object) is
   procedure Free is new Ada.Unchecked_Deallocation (...);
begin
   if This.Worker /= null then
      This.Worker.Shut_Down;
      Free (This.Worker);
   end if;
end Finalize;

which shall be rewritten as:

procedure Finalize (This : in out Object) is
   procedure Free is new Ada.Unchecked_Deallocation (...);
begin
   if This.Worker /= null then
      This.Worker.Shut_Down;
      while not Worker'Terminated loop
         delay 0.1;
      end loop;
      Free (This.Worker);
   end if;
end Finalize;

Is it so?

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