fpsettimeofday, milliseconds and vbox
lazarus / 32-Linux

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pkacperski · 2014-06-23 13:28

Hello
I've stumbled upon quite a strange problem with fpsettimeofday from
'BaseUnix' module.
I have this simple piece of code:
Code: [Select]procedure TForm1.Button1Click(Sender: TObject);
var
   tv : timeval;
begin
   fpgettimeofday(@tv, nil);
   Form1.Memo1.Append('tv.tv_sec = ' + IntToStr(tv.tv_sec) + ',
tv.tv_usec = ' + IntToStr(tv.tv_usec));
   tv.tv_usec := 30000;

   fpsettimeofday(@tv, nil);
   fpgettimeofday(@tv, nil);
   Form1.Memo1.Append('tv.tv_sec = ' + IntToStr(tv.tv_sec) + ',
tv.tv_usec = ' + IntToStr(tv.tv_usec));
end;              
I've tested this code on two systems: Ubuntu 64-bit running natively
on my PC and Ubuntu 32-bit running in Oracle VirtualBox hosted in the
former one.

When run on my PC, this code behaves as expected:
Code: [Select]tv.tv_sec = 1403529872, tv.tv_usec = 892197
tv.tv_sec = 1403529872, tv.tv_usec = 30009
tv.tv_sec = 1403529873, tv.tv_usec = 61792
tv.tv_sec = 1403529873, tv.tv_usec = 30029

...but when run on VBox, fpsettimeofday seems to ignore milliseconds
field and sets time as if it was set to 0:
Code: [Select]tv.tv_sec = 1403529999, tv.tv_usec = 708589
tv.tv_sec = 1403529999, tv.tv_usec = 322
tv.tv_sec = 1403529999, tv.tv_usec = 552320
tv.tv_sec = 1403529999, tv.tv_usec = 247

Any idea?

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marcov · 2014-06-23 13:53

On 32-bit it seems that the older stime() syscall is used instead of
settimeofday. Stime only sets the tv_sec part, so not the nanosecond
and timezone parts.

(unix/settimeo.inc, the define is set in linux/osdefs.inc)

I assume this was done for compatibility with older kernels, but
probably currently supported kernels don't need this anymore.