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Date: Tue, 27 Mar 2012 20:59:37 +0200
From: Christian Franke <Christian DOT Franke AT t-online DOT de>
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To: cygwin AT cygwin DOT com
Subject: Re: clock_getres(CLOCK_REALTIME, .) may return an outdated and too high resolution
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Corinna Vinschen wrote:
> 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.

No, again this is the minimum of all resolutions currently set by all 
processes.


>    The OS just doesn't support
> arbitrary values for the period.
>

Yes - but in 'actual' a smaller value than the value set for the current 
process may be returned.

Christian


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