Re: Ada.Real_Time behavior with GNAT

[george.priv@gmail.com]

On Mar 29, 9:51 am, kongra <kon...@gmail.com> wrote:
> Hi everybody.
>
> I have a question related to the Ada.Real_Time package. When I compile
> the following code using GNAT GPL 2007 on Windows XP SP2 I observe
> some strange looking behavior.
>
> with Ada.Real_Time;
> with Ada.Text_IO;
>
> procedure Timing is
>    Start_T : Ada.Real_Time.Time;
>    End_T   : Ada.Real_Time.Time;
>    Total_T : Duration;
>    Sleep_T : constant Duration := Duration (0.0001);
>
>    use Ada.Real_Time;
>
>    Val : Integer := 0;
> begin
>    -- delay Sleep_T;
>    Start_T := Ada.Real_Time.Clock;
>    for K in 1 .. 10 loop
>       for I in 1 .. 10_000_000 loop
>          Val := Val + I;
>       end loop;
>    end loop;
>    End_T   := Ada.Real_Time.Clock;
>    Total_T := Ada.Real_Time.To_Duration (End_T - Start_T);
>    Ada.Text_IO.Put_Line (Integer'Image (Val));
>    Ada.Text_IO.Put_Line (Duration'Image (Total_T));
> end Timing;
>
> The compilation command is pretty straightforward: gnatmake Timing.adb
> -o timing.exe. Running timing.exe I get
>
> 1432236160
> 0.000000000
>
> To my surprise the total time is 0 here, though performing all the
> computations takes some observable time. However removing comment in
> the line containing statement delay Sleep_T; causes
>
> 1432236160
> 0.431441426
>
> Apparently the total duration seems correct now. I get a similar
> change by putting
>
> with Ada.Calendar;
>
> to the compilation unit (without completely using it). Moreover the
> delay statement has got the same impact on the program execution even
> when it's placed in some procedure other than Timing and the procedure
> is not used at all.
>
> I tried the same code in a bigger project using switches like those in
> the Ada Wikibooks examples, getting the same.
>
> Can it be explained or is there something I don't know about timing in
> Ada ? I'm a beginner in Ada (after 7+ years Java coding) and I think
> it's a great programming language, worth to be promoted among
> students. But this one really surprised me even if I was able to avoid
> using Ada.Calendar (for example prohibited by Ravenscar profile) using
> a hack with delay.
>
> Best regards,
>
> Konrad Grzanek.

Your program should overflow (unless you suppress checks) raising
Constraint_Error for Val. It runs fine on Vista though after fixing
overflow problem

George.