Re: Simp,e example for 2 tasks

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Sun, 21 Sep 2014 06:31:28 -0700 (PDT), Stribor40 wrote:

> Would anyone be able to post simple example of ada program showing 2 tasks
> taking to each other please.  For example one task sends message to
> another saying "hi" and second taks replying "hi back".
 
> I am having troubles finding example of simple program like this online

Because there are problems with that:

1. It is bad design, tight coupling. There should never be so that two
object knew each other. Only one task may know another, e.g. client knows
server, server does not know any clients.

2. Sending messages is not the method of task communication. Tasks have
entry points which are alike to procedures not raw data (messages).

3. Messages as marshaled parameters of some asynchronous requests are not
implemented using tasks. There are protected objects which serve this
purpose in Ada.

4. It is not clear what sort of communication you want. Your description
misses many crucial design details required. E.g. are parameters (messages)
marshaled, is exchange synchronous, how knows whom etc.

Anyway, here is an example of text exchange between two tasks A and B:

with Ada.Strings.Unbounded;  use Ada.Strings.Unbounded;
with Ada.Text_IO;  use Ada.Text_IO; 

procedure Talk is
   task A is
      entry Ask (Message : in out Unbounded_String);
   end A;

   task B is
   end B;
   
   task body A is
   begin
      loop
         select
            accept Ask (Message : in out Unbounded_String) do
               Message := To_Unbounded_String ("Hi back");
            end Ask;
         or terminate;
         end select;
      end loop;
   end A;
   
   task body B is
      Message : Unbounded_String;
   begin
      Message := To_Unbounded_String ("Hi");
      Put_Line ("Send " & To_String (Message));
      A.Ask (Message);
      Put_Line ("Received " & To_String (Message));
   end B;

begin
   null;
end Talk;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de