Re: Strange behaviour of delay in Windows XP

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Thu, 07 Oct 2010 23:04:33 +0200, michael bode wrote:

> I've seen a very strange behaviour of the delay statement with GNAT on a
> Windows XP machine. This is the code:
> 
> with  Ada.Text_Io; use Ada.Text_Io;
> with Ada.Calendar; use Ada.Calendar;
> 
> procedure Testprog is
>    T1, T2 : Time;
>    D : Duration;
> begin
>    D := 1.0;
>    T1 := Clock;
>    delay D;
>    T2 := Clock;
>    Put_Line ("Expected delay:" & Duration'Image(D));
>    Put_Line ("Actual delay:" & Duration'Image(T2-T1));
> end Testprog;
> 
> And this is what it prints when run on Linux:
> 
> Expected delay: 1.000000000
> Actual delay: 1.000321000
> 
> But I have a (or rather 2) Dell Vostro MT 220 PC where the actual delay
> is about 2.7s instead.

What happens with this:

with Ada.Text_IO;    use Ada.Text_IO;
with Ada.Calendar;   use Ada.Calendar;
with Win32.Mmsystem; use Win32.Mmsystem;
with Win32.WinBase;  use Win32.WinBase;

procedure Testprog is
   T1, T2 : Time;
   D : Duration;
   use type Win32.BOOL;
begin
   if TIMERR_NOERROR /= timeBeginPeriod (1) then
      raise Program_Error;
   end if;
   if 0 = SetThreadPriority (GetCurrentThread,
THREAD_PRIORITY_TIME_CRITICAL) then
      raise Program_Error;
   end if;
   delay 1.0; -- Let the dust settle down
   D := 1.0;
   T1 := Clock;
   delay D;
   T2 := Clock;
   Put_Line ("Expected delay:" & Duration'Image(D));
   Put_Line ("Actual delay:" & Duration'Image(T2-T1));
end Testprog;

timeBeginPeriod (1) changes the resolution of timer to 1ms. Some older
systems had 10ms by default.

SetThreadPriority changes the priority to R-T.

> Any ideas or should I call a feng shui master?

Turn down indexing service, anti-virus software and whatever mess is
running on the computer in background.

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