Thread safety, especially HolidayManager (?)

[HoffmannTom]

More information

Hello,
I haven't found any information about thread safety. My profiler shows, that e.g. HolidayManager.createManager() is quite time consuming.
Therefore, I would like to cache the instances per country / region.
Is this possible or are there any known multi-threading issues?
I don't know if HolidayManager is thread-safe.

If you have any information about thread-safety, I would be glad to know.

Thanks a lot!