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Date: Tue, 27 Mar 2012 20:28:23 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: clock_getres(CLOCK_REALTIME, .) may return an outdated and too high resolution
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On Mar 27 20:01, Christian Franke wrote:
> Corinna Vinschen wrote:
> >On Mar 26 19:00, Christian Franke wrote:
> >>Corinna Vinschen wrote:
> >>>I see your point, but what bugs me a bit is the fact that
> >>>clock_getres(CLOCK_REALTIME) and clock_setres(CLOCK_REALTIME) will
> >>>always return the same value coarsest, regardless what value has been set.
> >>If clock_setres was called and succeeded, then clock_getres(.)
> >>should return the value set before.
> >>
> >>If clock_setres was not called, the coarsest value is IMO the only
> >>value that can be guaranteed.
> >>
> >>The actual value returned by NtQueryTimerResolution is simply
> >>useless in this context: It is the minimum of all resolutions
> >>currently set by all running processes. It may change at any time.
> >>There is apparently no way the query the current setting of the
> >>current process.
> >Uh, right, I misunderstood.  I reverted the change to clock_setres.
> 
> Sorry, I probably forgot to mention that NtSetTimerResolution
> returns the same useless actual value than NtQueryTimerResolution.
> 
> I would suggest:
> 
>     status = NtSetTimerResolution (period, TRUE, &actual);
>     if (!NT_SUCCESS (status))
>       { ... return -1; }
>  -  minperiod = actual;
>  +  minperiod = period;

But that's not right.  The "actual" value is not useless, but the value
the resolution has actually been set to.  The OS just doesn't support
arbitrary values for the period.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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