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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: Running a background task
Date: Thu, 15 May 2008 15:31:42 -0700 (PDT)
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Date: 2008-05-15T15:31:42-07:00
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On May 15, 1:51 pm, Bender <Jeffrey.S.Morri...@gmail.com> wrote:
> Hi, I'm pretty new to Ada, and need to figure out a way to kick off a
> background task that runs more or less forever, while normal execution
> of the program continues.
>
> Thus far I've figured out how to create a task and start it, but the
> procedure calling it requires the task to finish before continuing
> on.  I'm sure I just must be using the wrong mechanisms, but I can't
> really figure out the answer.

When Handle_Msg calls on the On_String entry, this starts a
rendezvous, and Handle_Msg stops when the rendezvous is done.  Since
the "accept" has a "do" part, the rendezvous will not be done until
the "do" completes, which in your case never happens.  Thus,
Handle_Msg will never proceed past the entry call.

It's hard for me to give a solution, since I don't know just what
you're trying to accomplish; but you may want to move the loop out of
the "accept".

                                 -- Adam


> Task definition
> ---------------------
> (spec)
> task type Poll_For_Status is
>   entry On_String (String : in SideAB)
> end Poll_For_Status;
>
> type Task_Access is access Poll_For_Status;
> Status_Task : Task_Access;
>
> (body)
>   task body Poll_For_Status is
>   begin
>     accept On_String (String : in SideAB) do
>       loop
>         delay 3.0
>         Send_Status_Req (String);
>       end loop;
>     end On_String;
>   end Poll_For_Status;
>
> Calling procedure
> ------------------------
> procedure Handle_Msg(...) is
>   String : SideAB;
>   ...
> begin
> ...
>   Status_Task := new Poll_For_Status
>   Status_Task.On_String (String);
> ...
>
> If I remove the loop in the task body, it works fine.  Putting it in
> seems to halt execution.
>
> Am I missing anything?