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From: "Anh Vo" <anhvofrcaus@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Designing Timers using Ada.Real_Time.Timing_Events package
Date: 27 Mar 2006 14:00:01 -0800
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Dmitry A. Kazakov wrote:
> On Mon, 27 Mar 2006 09:49:59 +0200, Dmitry A. Kazakov wrote:
>
> > -- Main entrance (is closed during notification) The reason is
> > -- to aviod irace condition upon timer event. Otherwise a task
> > -- might get it twice.
> > entry Wait_For when Inactive or not Occured is
> >    if Inactive then
> >       raise Timer_Canceled;
> >    else
> >       requeue Wait_Notify with abort;
> >    end if;
> > end Wait_For;
> >
> > -- The notification queue, this is a private entry point to gather
> > -- the waiting requests.
> > entry Wait_Notify when Inactive or Occured is
> >    if Inactive then
> >       raise Timer_Canceled;
>
> I forgot to reset it:
>
>    else
>       Occurred := Wait_Notify'Count > 0;
>
> >    end if;
> > end Wait_Notify;
> >
> > procedure Set (Period : Time_Span) is
> > begin
> >    -- attach Signal to the timer
> >    Inactive := False;
> > end Set;
> >
> > procedure Signal (...) is
> >    Occurred := True;
> > end Signal;
> >
> > procedure Stop is
> >    -- detach Signal from the timer
> >    Inactive := True;
> > end Stop;

Dmitry,

Before going further, I would like to know if this is exactly what you
had in mind. By the way, it is compilable.


with Ada.Real_Time.Timing_Events;

package Dmitry_Timers is

   use Ada;

   Timer_Canceled : exception;

   protected type Periodic_Timer is
      entry Wait_For;
      -- May raise Timer_Canceled
      procedure Set (Period : Real_Time.Time_Span);
      -- Sets. reset timer
      procedure Cancel;
      -- Stops timer. Any task in Wait_For queue gets Timer_Canceled
raised
      entry Simulate;
      -- Simulates a timer event
   private
      procedure Signal (Event: in out
Real_Time.Timing_Events.Timing_Event);
      -- To be set as a handler for Ada.Real_Time.Timing_Events
      -- [...]
      -- Some internal entry to requeue Wait_For, if Signal cannot
      -- be an entry, but must be a protected procedure, instead.
      entry Wait_Notify;

      Inactive : Boolean := True;
      Occurred : Boolean := False;
      The_Event : Real_Time.Timing_Events.Timing_Event;
   end Periodic_Timer;

end Dmitry_Timers;

package body Dmitry_Timers is

   protected body Periodic_Timer is
      entry Wait_For when Inactive or not Occurred is
      begin
         if Inactive then
            raise Timer_Canceled;
         else
            requeue Wait_Notify with abort;
         end if;
      end Wait_For;

      entry Wait_Notify when Inactive or Occurred is
      begin
         if Inactive then
            raise Timer_Canceled;
         else
            Occurred := Wait_Notify'Count > 0;
         end if;
      end Wait_Notify;

      procedure Set (Period : Real_Time.Time_Span) is
      begin
         Real_Time.Timing_Events.Set_Handler (The_Event, Period,
Signal'access);
      end Set;

      procedure Cancel is
         Success : Boolean := False;
         use type Ada.Real_Time.Timing_Events.Timing_Event_Handler;
      begin
         if Real_Time.Timing_Events.Current_Handler (The_Event) /= null
then
            Real_Time.Timing_Events.Cancel_Handler (The_Event,
Success);
            Inactive := True;
            Occurred := False;
         end if;
      end Cancel;

      entry Simulate when True is
      begin
         null; -- What does it do exactly???
      end Simulate;

      procedure Signal (Event: in out
Real_Time.Timing_Events.Timing_Event) is
      begin
         Occurred := True;
         -- Action to be performed.
      end Signal;

   end Periodic_Timer;

end Dmitry_Timers;

AV