There is a report that GC may not work correctly. Set -Djruby.native.enabled=false to avoid this problem.
Using C extension support with Warbler/wars/Tomcat
At the time of this writing we don't ship libjruby-cext.so in the jruby-jars gem. (That might be grounds for filing a bug/improvement ticket; please update this page if you decide to file one.)
To work around that fact, you'll need to do the following:
Locate libjruby-cext.so and libjffi-1.0.so out of the JRuby binary distribution'slib/native/[platform] directory. Be sure to choose the right directory for your platform.
Copy them somewhere on the system (e.g., /opt/jruby/lib), and either modify the places where ld.so looks for libraries to add that path or set LD_LIBRARY_PATH (or equivalent) to use that path before launching the JVM process that uses JRuby (Tomcat/application server etc.).