Re: RE : [fpc-devel] Problem with Now() and time changed by ntpd

[zeljko]

On Thursday 03 of November 2011 21:30:19 Sven Barth wrote:
 Am 02.11.2011 19:25, schrieb Ludo Brands:
  Apparently not everything is that transparent under windows:
  http://msdn.microsoft.com/en-us/library/windows/desktop/ms724944%28v=vs.8
  5%2 9.aspx
  
  To inform Explorer that the time zone has changed, send the
  WM_SETTINGCHANGE message.
 
 WM_SETTINGCHANGE simply notifies you that the user changed the time
 zone, because otherwise you might not be able to detect that (except you
 read the settings from the registry yourself).
 
  Or:
  
  http://channel9.msdn.com/coding4fun/articles/Changing-time-zones
  
  By itself, changing the time zone doesn't have any apparent effect
  except in new processes.  In order to see the change, you need to send a
  system notification message.  This notification is made by calling
  SendMessageTimeout with WM_SettingChange and a parameter of intl. 
 
 This is wrong. Changing the timezone effects e.g. all following calls to
 GetLocalTime. See the following example program:
 
 === source begin ===
 
 program timezonetest;
 
 {$apptype console}
 {$mode objfpc}{$H+}
 
 uses
SysUtils;
 
 begin
Writeln(FormatDateTime('c', Now));
Writeln('Please change the timezone and then press enter');
Readln;
Writeln(FormatDateTime('c', Now));
Writeln('Done');
Readln;
 end.
 
 === source end ===
 
 As you see there is no message processing.
 
 My normal timezone is Berlin. Now I've run the program and changed the
 timezone to Greenland (-3h). The output was the following:
 
 === output begin ===
 
 03.11.2011 21:16:33
 Please change the timezone and then press enter
 
 03.11.2011 17:17:10
 Done
 
 === output end ===
 
 So your link which talks about only affects new processes is proven
 wrong.

But this is on windows ? On linux it does not work without re-reading tzdata.

zeljko
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Re: RE : [fpc-devel] Problem with Now() and time changed by ntpd

[Sven Barth]

Am 04.11.2011 07:55, schrieb zeljko:

But this is on windows ? On linux it does not work without re-reading
tzdata.


Yes, this is Windows only. It was meant as a prove that a timezone 
change does influence running processes as well (and not only new ones 
as that link stated).


Regards,
Sven
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Re: RE : [fpc-devel] Problem with Now() and time changed by ntpd

[Sven Barth]

Am 02.11.2011 19:25, schrieb Ludo Brands:

Apparently not everything is that transparent under windows:
http://msdn.microsoft.com/en-us/library/windows/desktop/ms724944%28v=vs.85%2
9.aspx

To inform Explorer that the time zone has changed, send the
WM_SETTINGCHANGE message.



WM_SETTINGCHANGE simply notifies you that the user changed the time 
zone, because otherwise you might not be able to detect that (except you 
read the settings from the registry yourself).



Or:

http://channel9.msdn.com/coding4fun/articles/Changing-time-zones

By itself, changing the time zone doesn't have any apparent effect except
in new processes.  In order to see the change, you need to send a system
notification message.  This notification is made by calling
SendMessageTimeout with WM_SettingChange and a parameter of intl. 


This is wrong. Changing the timezone effects e.g. all following calls to 
GetLocalTime. See the following example program:


=== source begin ===

program timezonetest;

{$apptype console}
{$mode objfpc}{$H+}

uses
  SysUtils;

begin
  Writeln(FormatDateTime('c', Now));
  Writeln('Please change the timezone and then press enter');
  Readln;
  Writeln(FormatDateTime('c', Now));
  Writeln('Done');
  Readln;
end.

=== source end ===

As you see there is no message processing.

My normal timezone is Berlin. Now I've run the program and changed the 
timezone to Greenland (-3h). The output was the following:


=== output begin ===

03.11.2011 21:16:33
Please change the timezone and then press enter

03.11.2011 17:17:10
Done

=== output end ===

So your link which talks about only affects new processes is proven wrong.

Regards,
Sven
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Re: RE : [fpc-devel] Problem with Now() and time changed by ntpd

[Hans-Peter Diettrich]

Ludo Brands schrieb:
debated). Also note that on platforms like Windows this would be a 
unnecessary call as there the current(!) timezone bias is 
located in a 
shared memory area which is mapped into each process by the kernel.




Apparently not everything is that transparent under windows: 
http://msdn.microsoft.com/en-us/library/windows/desktop/ms724944%28v=vs.85%2

9.aspx

To inform Explorer that the time zone has changed, send the
WM_SETTINGCHANGE message.

Or:

http://channel9.msdn.com/coding4fun/articles/Changing-time-zones

By itself, changing the time zone doesn't have any apparent effect except
in new processes.  In order to see the change, you need to send a system
notification message.  This notification is made by calling
SendMessageTimeout with WM_SettingChange and a parameter of intl. 


There exists a more specific WM_TIMECHANGE message, with the remark:

An application should not broadcast this message, because the system 
will broadcast this message when the application changes the system time.



It remains unclear whether a DST change will cause such an broadcast as 
well. Most probably *not*, because the system time (UTC) is not affected 
by DST or timezone changes.


DoDi

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