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Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!usc!bloom-beacon!mit-eddie!uw-beaver!uw-june!fred.cs.washington.edu!tancheeh
From: tancheeh@fred.cs.washington.edu (Nicholas Tan Chee Hiang)
Newsgroups: comp.lang.ada
Subject: shared variable between tasks
Message-ID: <8610@june.cs.washington.edu>
Date: 29 Jun 89 02:07:58 GMT
Sender: news@june.cs.washington.edu
Reply-To: tancheeh@fred.cs.washington.edu (Nicholas Tan Chee Hiang)
Organization: University of Washington, Computer Science, Seattle
List-Id: <comp.lang.ada>

I am trying to understand concurrency in Ada.  Can someone please tell
me why the variable Unprotected below is never updated?  Thanks!

- N

------------------------------>code below<------------------------------

with Text_IO;  use Text_IO;

procedure Unprotected_Shared_Variable is
  Unprotected : Character := '*';
  pragma SHARED(Unprotected);

  task Write_Letter_A_To_Variable;
  task Access_Variable;

  task body Write_Letter_A_To_Variable is
    Letter : constant Character := 'A';
  begin
    loop
      Unprotected := Letter;
      delay 0.5;
    end loop;
  end Write_Letter_A_To_Variable;

  task body Access_Variable is
    Letter : Character := Unprotected;
  begin
    loop
      Put (Letter);
      delay 3.0;
    end loop;
  end Access_Variable;

begin
  null;
end Unprotected_Shared_Variable;