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From: lutz@iks-jena.de (Lutz Donnerhacke)
Newsgroups: comp.lang.ada
Subject: Re: Same two tasks in two rendezvous?
Date: Tue, 31 Jul 2001 10:02:43 +0000 (UTC)
Organization: IKS GmbH Jena
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* Adam Beneschan wrote:
>Is it possible for two tasks, T1 and T2, to be in two rendezvous with
>each other simultaneously?

No.

>Is this what should actually happen?

Deadlock.

>Is there anything in the language that prohibits this from happening?

No, because it's possible to open the deadlock by a third task.

with Ada.Text_IO;
use Ada.Text_IO;

procedure t is
   task type rev is
      entry e1;
      entry e2;
   end;
   
   task body rev is
   begin
      Put_Line ("Starting task");
      accept e1 do
         Put_Line ("Entry E1");
         accept e2 do
            Put_Line ("Entry E2");
         end e2;
      end e1;
      Put_Line ("Stopping task");
   end;
   
   e : rev;
   
   task type helper;
   task body helper is
   begin
      Put_Line ("Starting helper task");
      e.e2;
      Put_Line ("Stopping helper task");
   end helper;
   
   h : helper;                      --  comment this out to see what happens
      
begin
   Put_Line ("First Rendevous");
   e.e1;
   Put_Line ("Second Rendevous");   --  comment this out to see what happens
   e.e2;                            --  comment this out to see what happens
   Put_Line ("Stopping Main Task");
end t;