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From: franke@minet.uni-jena.de (Frank Ecke)
Subject: Re: an error in Re: tasking
Date: 1998/10/07
Message-ID: <slrn71n73j.c0v.franke@pax01f.mipool.uni-jena.de>#1/1
X-Deja-AN: 398689327
References: <361B31AA.6714@ipnsun5.in2p3.fr> <361B3260.7475@ipnsun5.in2p3.fr>
Organization: Department of Computer Science, FSU Jena, Germany
Reply-To: franke@minet.uni-jena.de
Newsgroups: comp.lang.ada
Date: 1998-10-07T00:00:00+00:00
List-Id: <comp.lang.ada>

On Wed, 07 Oct 1998 11:20:32 +0200, grave <grave@ipnsun5.in2p3.fr> wrote:

> I'm wanting to kill a task to let an exception propagate and kill the
> process.  How can I do this if the task is already excuting some part of
> code like this :
> 
> select
>    entry start;
>    Do_Some_Stuff_Here;
> or
>    terminate;
> end select;
> 
> Here I'm wanting to kill the task when it works in Do_Some_Stuff_Here;
> 
> Is this possible ?


You select should read

   select
      accept Start;
      Do_Some_Stuff_Here;
   or
      terminate;
   end select;

for it is not possible to declare an entry within a branch of a select
statement.

   To kill (or abort) a task, use ``abort Task_Name {, Task_Name};'' (see
ARM 9.8).  In order to abort the task from within Do_Some_Stuff_Here (i.e., to
let that task kill itself), you may issue

   Self : Ada.Task_Identification.Task_ID :=
     Ada.Task_Identification.Current_Task;

   ...

   Ada.Task_Identification.Abort_Task(Self);

   Note that trying to kill the task (from outside) ``when it works in
Do_Some_Stuff_Here'' gives raise to a race condition since you cannot be sure
that the task to be killed is already (or still) inside Do_Some_Stuff_Here when
you issue the abort.

   Note further that if Do_Some_Stuff_Here were part of the accept statement
corresponding to the Start entry, it would be executed as part of an abort-
deferred operation, namely the rendezvous between the caller and the callee,
and could thus not be aborted.

> I'm wanting to kill a task to let an exception propagate and kill the
> process.

I am a bit puzzled by this statement.  Could you please give further
explanations?


Frank

--
Frank Ecke <franke@minet.uni-jena.de>


       In a world without walls and fences, who needs windows and gates?