WITHDRAWN: RFR: 8180466: Clock.systemUTC has low resolution on Windows

[David Holmes]

Closing this issue as "will not fix"

David

On 28/02/2019 3:54 am, Thomas Stüfe wrote:
> 
> 
> On Wed, Feb 27, 2019 at 8:20 AM David Holmes <david.holmes at oracle.com 
> <mailto:david.holmes at oracle.com>> wrote:
> 
>     Hi Thomas,
> 
>     I'm starting think I will have to close this as "will not fix".
>     There is
>     the performance aspect of the call itself to be potentially concerned
>     about - though it would put it on a par with nanoTime() so I'm not that
>     concerned. But I've also read that it can have problems during "system
>     time adjustments" [1]
> 
>     "The high resolution of GetSystemTimePreciseAsFileTime() is derived
>     from
>     the performance counter value at the time of the call and the
>     performance counter frequency. However, the performance counter
>     frequency should be corrected during system time adjustments to
>     adapt to
>     the modified progress in time. Current Windows versions don't do this.
>     The obtained microsecond part may be severely affected when system time
>     adjustments are active. ... As of Windows 10 (Build 10240), the
>     inaccuracy of GetSystemTimePreciseAsFileTime() during system time
>     adjustments persists."
> 
>     That sounds like something that may introduce very obscure bugs. :(
> 
>     David
>     -----
> 
> 
> I agree, sorry for the lost work, but that sounds risky.
> 
> ..Thomas
> 
> 
>     This is a very interesting read!
>     [1] http://www.windowstimestamp.com/description
> 
>     On 26/02/2019 11:12 pm, David Holmes wrote:
>      > Hi Thomas,
>      >
>      > On 26/02/2019 8:54 pm, Thomas Stüfe wrote:
>      >> Looks good.
>      >
>      > Thanks for taking a look.
>      >
>      >> I read somewhere that the ..precise.. API comes with a performance
>      >> penalty, is that in some way measurable?
>      >
>      > Not easily as I don't have a machine I can directly run
>     measurements on,
>      > but I'll do some more research and see what I can do.
>      >
>      > Thanks,
>      > David
>      >
>      >> Cheers, Thomas
>      >>
>      >> On Tue, Feb 26, 2019 at 1:32 AM David Holmes
>     <david.holmes at oracle.com <mailto:david.holmes at oracle.com>
>      >> <mailto:david.holmes at oracle.com
>     <mailto:david.holmes at oracle.com>>> wrote:
>      >>
>      >>     bug: https://bugs.openjdk.java.net/browse/JDK-8180466
>      >>     webrev: http://cr.openjdk.java.net/~dholmes/8180466/webrev/
>      >>
>      >>     There is a new higher-resolution system time call available in
>      >> Windows
>      >>     8+ and Windows Server 2012+. This enhancement uses the API
>     if it is
>      >>     available at runtime.
>      >>
>      >>     Testing:
>      >>        - manual testing using the little "benchmark" in the bug
>     report on
>      >>     Windows 7 (no new API) and later
>      >>        - java.time tests
>      >>
>      >>     Thanks,
>      >>     David
>      >>
>