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From: "Steve" <nospam_steved94@comcast.net>
Newsgroups: comp.lang.ada
References: <20050804161000.1ffa591b@localhost>
Subject: Re: Newbie: Code isn't executed
Date: Thu, 4 Aug 2005 19:43:09 -0700
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Date: 2005-08-04T19:43:09-07:00
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"Thomas Ruschival" <Thomas@ruschival.de> wrote in message 
news:20050804161000.1ffa591b@localhost...
> Hello Ada group
> I am a student learning Ada at university. I played with some tasks
> that want to join another task for a rendevouz, its a modiefied exaple
> from the lectures. Basically I let 2 tasks sleep a different amount of
> time then wake up and execute a piece of code with another task during
> a rendevouz, I count the number how often a task got executed.
> Somehow a piece of code never gets executed - neither me nor nor my
> tutor has a clue why -- here is the code:
>
> Thanks for _ANY_ comments - I know this isn't the best way of coding -
> but it was just meant as an example until strange things happened
>
> Thomas
>
First:
  I recommend you add something like:

    EXCEPTION
      WHEN Reason: OTHERS =>
        Ada.Text_IO.Put( "EXCEPTION NAME: " & Exception_Name( Reason) );
        Ada.Text_IO.Put( "EXCEPTION MESSAGE: " & Exception_Message( 
Reason) ) );
        Ada.Text_IO.Put( "EXCEPTION INFORMATION: " & 
Exception_Information( Reason) ) );

To the end of each of task body, at least for experimenting.  This helps to 
eliminate the problem of tasks dying quietly.

Second:
  You may be aware of this, but there are a lot of holes in the program.
  It is generally not safe to have 2 tasks manipulating the same global 
memory without the use of a protected type.  In your example, I think it 
would make more sense to pass information to Susan at Dinner:

task Susan is
  entry Dinner( Partner : Name );
end Susanl

...

Then instead of:
  Partner := Peter;
  Susan.Dinner;

use:
  Susan.Dinner( Peter );

Also, it is a good idea to avoid doing much inside a rendevous other than 
moving data around, so I would suggest changing:

  dinnerPartner : Name;
  ...
  accept Dinner( Partner : Name ) do
     dinnerPartner := Partner;
  end Dinner
  stat(dinnerPartner ) := stat(dinnerPartner )+1;
  Put("Susan is having dinner with...."& Name'Image(dinnerPartner ));
  New_Line;

During the rendevous only one of the threads runs, so I suggest getting it 
over as soon as possible.

Steve
(The Duck)