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From: "John B. Matthews" <nospam@nospam.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Barrier re-evaluation issue with GNAT 4.3.2
Date: Thu, 01 Oct 2009 12:12:47 -0400
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Date: 2009-10-01T12:12:47-04:00
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In article <nospam-12AAE0.11590930092009@news.aioe.org>,
 "John B. Matthews" <nospam@nospam.invalid> wrote:

[...]
> Another alternative, suggested by Dmitry A. Kazakov, is to replace 
> entry Wait with procedure Wait, which obviates the need for Signal: 

Sorry, I carelessly posted code with a busy-wait. Please consider this 
alternative, which polls the timer's state:

with Ada.Text_IO;
with Alarm_Clock;

procedure Main is
   My_Alarm : Alarm_Clock.Alarm_Type;
begin
   Ada.Text_IO.Put_Line ("Setting alarm ...");
   My_Alarm.Set;

   Ada.Text_IO.Put_Line ("Waiting for alarm ...");
   My_Alarm.Wait;

   Ada.Text_IO.Put_Line ("ALARM!!");
end Main;

package Alarm_Clock is

   type Alarm_Type is tagged null record;
   procedure Set(Alarm : Alarm_Type);
   procedure Wait(Alarm : Alarm_Type);

end Alarm_Clock;

with Ada.Real_Time.Timing_Events;

package body Alarm_Clock is

   use Ada.Real_Time;
   Timer : Timing_Events.Timing_Event;
   Fired : Boolean := False;

   protected Clock is
      procedure Wakeup(Event : in out Timing_Events.Timing_Event);
   end Clock;

   protected body Clock is
      procedure Wakeup(Event : in out Timing_Events.Timing_Event) is
      begin
         Fired := True;
      end Wakeup;
   end Clock;

   procedure Set(Alarm : Alarm_Type) is
   begin
      Timer.Set_Handler(In_Time => Seconds(3),
                        Handler => Clock.Wakeup'Access);
   end Set;

   procedure Wait(Alarm : Alarm_Type) is
   begin
      loop
         delay 1.0;
         exit when Fired;
      end loop;
   end Wait;

end Alarm_Clock;


-- 
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>