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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Tail recursion upon task destruction
Date: Tue, 17 Nov 2009 15:38:45 -0600
Organization: Jacob Sparre Andersen
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Date: 2009-11-17T15:38:45-06:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:jv8fpjlb56be$.1afg8uuwigjop$.dlg@40tude.net...
> Consider a task encapsulated in an object in either way:
>
>   type Device is
>      Driver : Driver_Task (Device'Access);
>
> or
>
>   type Device is
>      Driver : not null access Driver_Task := Driver_Task (Device'Access);
>
> Let the object is allocated dynamically and we wanted to destroy it from
> the task.

Ada does not allow an object to destroy/free itself. That's generally a good 
thing, because such an object cannot be an ADT (it cannot be used as the 
element of a container, for instance), and such a model would require a far 
more complex scheme of frame completion than is used now: wait for all taks, 
then finalize all objects, then free all memory.

I realize that there are a few cases where some other scheme would be better 
(we struggled with this in CLAW, as the finalization of library level 
objects tried to use the GUI task which of course has already terminated), 
but they would require such an earthquake in semantics as not to make any 
sense for Ada.

In your particular case, I don't understand why you don't use nesting to 
solve the problem. That is, put the objectinside of the task (either 
directly or logically), so it can be destroyed when the task needs to do 
that. That would look something like:

   task type Device;

  task type Device is
      Device_Data : not null access Device_Data_Type := new 
Device_Data_Type;
  begin
      ...
      Free (Device_Data);
  end Device;

Note: you'd need a named access type to actually do this - I used an 
anonymous one simply to make my point clearer.

                               Randy.