Re: [boost] xtime and GetSystemTimeAsFileTime

From: William Kempf (williamkempf_at_[hidden])
Date: 2002-07-01 06:55:23

>From: "Simon J. Julier" <sjulier_at_[hidden]>
>
>A colleague of mine (Reinhold Behringer at RSC) drew my attention to the 
>fact that there is a problem with the Windows implementation of 
>xtime_get(.) because it uses GetSystemTimeAsFileTime. There are two 
>documented problems with this Win32 API function:
>
>1. The Windows system timer runs between 10ms and 55ms, depending on the 
>version of Windows used 
>(http://msdn.microsoft.com/library/default.asp?url=/library/en-us/sysinfo/ti 
>me_5h2d.asp). Reinhold tells me that the value returned by 
>GetSystemTimeAsFileTime seems to update at the same rate.

This one I consider a non-issue.  The xtime stuff does not promise any kind 
of granularity, so a 10-55ms variation on different Windows platforms is not 
a "violation" of the implied contract here.

>2. "If GetSystemTimeAsFileTime() is called at the precise split second 
>during which the date changes from one day to the next (12:00:00.000 AM), 
>the API may return a value indicating 12:00 AM for the previous day." 
>(Synopsis from 
>http://support.microsoft.com/default.aspx?scid=kb;EN-US;q224423). This bug 
>affects Windows 9x and Me.

This is a little more troubling, but it seems fairly unlikely to be an 
actual issue.  I'll check the KB article for work arounds (probably just 
call it twice if it reports 12:00 AM) and apply them for the next release.

Bill Kempf
>Has anybody looked at these issues?
>
>Cheers,
>
>Simon
>
>
>
>
>
>
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Bill Kempf
williamkempf_at_[hidden]

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