JRuby maps Ruby threads to Java threads, which are usually mapped directly to native threads. This means a simple Ruby Thread.new { } produces a real OS thread that runs concurrently with the parent thread. JRuby provides the same concurrency primitives as standard Ruby in the 'thread' library (loaded by default in 1.9 mode). Mutex, ConditionVariable, Queue, and friends all work as they do in MRI,
