JIT Compiler Specification

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.