RFR: 8283681: Improve ZonedDateTime offset handling [v2]

[Claes Redestad]

On Fri, 25 Mar 2022 14:09:03 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add nanoOfSecond parameter, make micro less reliant on constants
>
> src/java.base/share/classes/java/time/ZoneRegion.java line 183:
> 
>> 181:     @Override
>> 182:     /* package-private */ ZoneOffset getOffset(long epochSecond) {
>> 183:         return getRules().getOffset(Instant.ofEpochSecond(epochSecond));
> 
> The nanoAdjustment passed to `ofEpochSecond` is discarded in this code.
> It may be larger than a second;  see `Instant.ofEpochSecond(sec, nano)` for the details.
> Adding a second parameter to the `getOffset` method could be the remedy.

Done.

Sadly it seems the smaller improvement I got on `getYearFromMillisZoneRegion/-UTC` was due avoiding the added arithmetic in `Instant.ofEpochSecond(sec, nanos)`:

Benchmark                                     Mode  Cnt   Score   Error   Units
GetYearBench.getYearFromMillisZoneOffset     thrpt   15  27.579 ? 0.030  ops/ms
GetYearBench.getYearFromMillisZoneRegion     thrpt   15   9.570 ? 0.091  ops/ms
GetYearBench.getYearFromMillisZoneRegionUTC  thrpt   15  28.063 ? 0.030  ops/ms

Benchmark                                     Mode  Cnt   Score   Error   Units
GetYearBench.getYearFromMillisZoneOffset     thrpt   15  34.791 ? 0.030  ops/ms
GetYearBench.getYearFromMillisZoneRegion     thrpt   15   9.526 ? 0.122  ops/ms
GetYearBench.getYearFromMillisZoneRegionUTC  thrpt   15  28.056 ? 0.040  ops/ms


`getYearFromMillisZoneOffset` is still good.

-------------

PR: https://git.openjdk.java.net/jdk/pull/7957