[boost] Re: [date_time] enabling microsec_clock under C++Builder

From: Johan Nilsson (johan.nilsson_at_[hidden])
Date: 2003-03-28 02:34:01

"Russell Hind" <rhind_at_[hidden]> wrote in message
news:b5v56m$eo3$1_at_main.gmane.org...
> Johan Nilsson wrote:
> >
> > Perhaps, but one should consider that GetSystemTime promises 1ms
resolution
> > and delivers 10-15ms (and, IIRC,  that GetSystemTimeAsFileTime promises
> > 250ns resolution).
> >
>
> The Platform SDK states that the tickcount (GetTickCount) is updated
> every 10ms on NT3.51 and hight so I guess that GetSystemTime is updated
> at this interval also.

That's correct for uniprocessor machines.  It is normally 15ms on SMP
machines (at least on NT 4.0 upwards). As I said earlier, my only experience
is with x86 machines (and NT, not Win9x et al).

>
> FileTimes are measured in 100 nanosecond intervals since 1 January,
> 1601, but are you sure that GetSystemTimeAsFileTime will return a value
> that is updated at 250ns intervals?  I can't find anything in the SDK to
> say what the update interval is for the SystemTime, I'm just guessing
> that it is updated when the tick count is.

Sorry - just a case of bad memory - 100ns is of course correct.

I am definitely sure that GetSystemTimeAsFileTime will _not_ return a value
that is updated more frequently than the system's tick interval. I just
wanted to point out the similarity between:
- GSTAFT having a 100ns resolution but not being updated more often than
10-15ms
- microsec_clock having a microsec resolution but not being updated more
often than 10-15ms

// Johan