I created a flight recording of a Ruby script, running on JRuby. In the recording I can see a lot of File Read events where the "Bytes Read" attribute is "-1". (I also noticed that the Path attribute is empty).

JDK version: Java HotSpot(TM) 64-Bit Server VM (1.9.0-ea-b84) for windows-amd64 JRE (1.9.0-ea-b84), built on Oct 1 2015 02:02:32 by "java_re" with MS VC++ 12.0 (VS2013)

JRuby version: jruby-complete-9.0.1.0.jar

I don't know if it matters at all, but the Ruby script basically uses system calls ("java -version") to map where different versions of the JVM are installed.