Have you tried it yet? Jruby will try to spawn a second independent interpreter in its own thread on the same JVM rather than actually forking an OS process if

Have you tried it yet? Jruby will try to spawn a second independent interpreter in its own thread on the same JVM rather than actually forking an OS process if it detects that you're spawning another Ruby process. This is not without its drawbacks, but can be surprisingly handy. Your message passing code might Just Work with no alterations. There are ways for JRuby to do an actual real live OS fork, but they aren't especially pretty.