MaxGekk opened a new pull request #28824:
URL: https://github.com/apache/spark/pull/28824
### What changes were proposed in this pull request?
1. Set the given time zone as the first parameter of
`RebaseDateTime`.`rebaseJulianToGregorianMicros()` and
`rebaseGregorianToJulianMicros()` to Java 7 `GregorianCalendar`.
```scala
val cal = new Calendar.Builder()
// `gregory` is a hybrid calendar that supports both the Julian and
Gregorian calendar systems
.setCalendarType("gregory")
...
.setTimeZone(tz)
.build()
```
This makes the instance of the calendar independent from the default JVM
time zone.
2. Change type of the first parameter from `ZoneId` to `TimeZone`. This
allows to avoid unnecessary conversion from `TimeZone` to `ZoneId`, for example
in
```scala
def rebaseJulianToGregorianMicros(micros: Long): Long = {
...
if (rebaseRecord == null || micros < rebaseRecord.switches(0)) {
rebaseJulianToGregorianMicros(timeZone.toZoneId, micros)
```
and back to `TimeZone` inside of `rebaseJulianToGregorianMicros(zoneId:
ZoneId, ...)`
3. Modify tests in `RebaseDateTimeSuite`, and set the default JVM time zone
only for functions that depend on it.
### Why are the changes needed?
1. Ignoring passed parameter and use a global variable is bad practice.
2. Dependency from the global state doesn't allow to run the function in
parallel otherwise there is non-zero probability that the function may return
wrong result if the default JVM is changed during their execution.
3. This open opportunity for parallelisation of JSON files generation
`gregorian-julian-rebase-micros.json` and
`julian-gregorian-rebase-micros.json`. Currently, the tests `generate
'gregorian-julian-rebase-micros.json'` and `generate
'julian-gregorian-rebase-micros.json'` generates the JSON files by iterating
over all time zones sequentially w/ step of 1 week. Due to the large step, we
can miss some spikes in diffs between 2 calendars (Java 8 Gregorian and Java 7
hybrid calendars) as the PR https://github.com/apache/spark/pull/28787 fixed.
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
By running existing tests from `RebaseDateTimeSuite`.
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