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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Designing Timers using Ada.Real_Time.Timing_Events package
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Date: Tue, 28 Mar 2006 09:51:22 +0200
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Date: 2006-03-28T09:51:22+02:00
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On 27 Mar 2006 14:00:01 -0800, Anh Vo wrote:

> 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);
++++++++++++++++
Inactive := False;

>       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???

Emulates a premature timer event. It could be a direct call to Signal:

   Signal (The_Event);

It can be a procedure rather than entry, because Signal is a procedure.

>       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;

I cannot comment on Real_Time.Timing_Events, I have no any experience of
using it...

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