The JIT compiler in JRuby runs when executing interpreted code.

• The default threshold for a method body to compile is 50 invocations.
• Compilation of a method includes compilation of all contained closures.
• Closure bodies will not compile alone; the containing method must compile.
• JITted methods are single-method transient classes, loaded into their own classloaders using unique class names and thrown away when the method that references the class instance goes away.