There was (is?) a time, where JRuby couldnt pass the ruby spec because of their IO abstraction written in Java. They changed that code to be written in ruby ins

There was (is?) a time, where JRuby couldnt pass the ruby spec because of their IO abstraction written in Java. They changed that code to be written in ruby instead, with FFI to call out to libc, which made it more correct but slower, afaik.