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

[Henry Vermaak]

On 01/11/11 11:08, Michael Van Canneyt wrote:
>
>
> On Tue, 1 Nov 2011, Henry Vermaak wrote:
>
>> On 01/11/11 10:30, Michael Van Canneyt wrote:
>>> We'll simply need to store the next moment when the DST correction
>>> changes, compare the result of gettimeofday with that and re-base the
>>> time calculation. If we decide to add some check for the timestamp of
>>> the timezone file - that would make Date(), Time() and Now() VERY
>>> expensive operations.
>>
>> This seems to be what libc does (from looking at an strace of some gcc
>> binary).
>
> Correct (I had checked as well), but the only purpose that serves is to
> check whether the system timezone info has changed.
>
> This is something that normally doesn't happen unless you move your
> system from one timezone to another or during system setup, so I
> question the desirability of this check.

If you don't do this, daemons that were started before e.g. a daylight 
savings update will report the wrong time after the update.  Rather 
solve this correctly than take short cuts because you want to keep the 
time functions "fast".  Someone can always add performance timing 
helpers that use the correct functions on various OSes.

Henry