I just installed jruby 9.2.11.0 on MacOS Mojave 
typing irb greeted with this message
```WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by com.headius.backport9.modules.Modules to method sun.nio.ch.NativeThread.signal(long)
WARNING: Please consider reporting this to the maintainers of com.headius.backport9.modules.Modules
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release```
as it says to report to maintainers, hence reporting