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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Interresting difference in Normal-Returns/Expression-Functions
 and Extended-Returns.
Date: Tue, 23 Apr 2013 17:33:20 +0100
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Date: 2013-04-23T17:33:20+01:00
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Shark8 <onewingedshark@gmail.com> writes:

> I recently ran into unexpected behavior in the differences between a
> normal return and an extended return [in GNAT]: namely an extended
> return used to generate items in an array of tasks will *ALWAYS*
> execute in a sequential manner whereas the array generated with an
> expression-function or normal return is executed simultaneously.
>
> Is there some subtle difference in the extended return that I'm
> unaware of? (Is this a bug?)

I'm pretty sure you've found a bug.

I changed Testing to have an entry Start, and changed the body to report
when the task was activated:

   task type Testing( Text : not null access constant String ) is
      entry Start;
   end Testing;

   task body Testing is
      D : Duration := RNG.Random; -- Get a random duration.
   begin
      Resource.Write (Text.all & " starting.");
      accept Start;
      delay  D; -- Delay for that duration.
                -- Then print the Text for the task as well as the Delay.
      Resource.Write( Text.all & ASCII.HT & Duration'Image(D) );
   end Testing;

and changed the three test loops to start the tasks

    begin
       for T of P loop
          T.Start;
       end loop;
    end TEST_3;

The expression function and normal return function versions were fine;
the extended return function version prints

   TEST_3:	Extended Return Function
   Bob starting.

and hangs.