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

[michael.vancanneyt at wisa.be]

On Wed, 2 Nov 2011, Jonas Maebe wrote:

> Marco van de Voort wrote on Wed, 02 Nov 2011:
>
>> The point was just some encouragement to look further than the immediate
>> need though, and keep the time call relatively cheap. That doesn't exclude
>> being correct, it just means a more elaborate implementation.
>
> I do not think that reporting the time correctly taking into account the 
> current time zone and daylight savings time is a function that needs to be 
> treated as performance-critical.

Under some (not so uncommon) circumstances it is, e.g. for logging facilities.
Our own eventlog facility would suffer from this.

>> But harddisk latency can easily be in the half a second to second magnitude
>> (and then I don't even count spindowns, and am I accessing directories that
>> I continously access).
>
> If you are stat'ing that file for changes all the time, either the result 
> will be cached or the hard drive won't spin down. And stat'ing a file will 
> not take half a second when done repeatedly.

I tested this yesterday, using the following sequence:

fpGettimeOfDay();
if UseStat then
   fpStat('/etc/timezone');
fpGetTimeOfDay();

The sequence becomes 3 times slower when UseStat is true.

Michael.