Re: an error in Re: tasking

[franke@minet.uni-jena.de (Frank Ecke)]

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?