Today, I attended a tech talk by ThoughtWorks’ Ola Bini on JRuby (JRuby Wikipedia entry here).

I keep hearing great things about JRuby (even Matz has good things to say about it), and it’s nice to hear this from the horse’s mouth as well (Ola is one of the JRuby core developers). Apparently the latest version is highly compatible with Ruby 1.8.6, although applications that use native C extensions are not supported. It’s also impressive how far JRuby has come in terms of performance. Until about a year or so ago, it was still significantly slower than the standard Ruby 1.8 interpreter. Not only have they caught up since then, but the latest JRuby version running on the latest JVM (in server mode) is actually several times faster than the Ruby 1.9 interpreter (aka YARV), which in turn is several times faster than Ruby 1.8 (apparently up to 50x in benchmarks, but more like 1.5x on average). That’s quite an achievement!

The tight integration between JRuby and Java is very impressive. You can explore this by using jirb, JRuby’s version of irb. In this console, you can use all the standard Ruby classes and constructs, as well as Java classes and libraries (Ola demoed this by creating a Swing window and a button, with a listener implemented in Ruby). It really seems quite seamless and powerful.

Due to time constraints, Ola did not talk much about JRuby and Rails (I suppose his JRuby on Rails book would describe this in sufficient detail), but it sounds like it is pretty well supported by now. In fact, ThoughtWorks is shipping Mingle, a shrink-wrap agile project collaboration tool built in Rails and deployed on JRuby. Ola also cited several other large scale JRuby deployments at Oracle and SUN. In many cases, using JRuby proved to be a way in the door for development teams that wanted to use Ruby but whose IT organizations had standardized on Java and were not prepared to support another runtime.

Ola mentioned the GlassFish gem as a convenient way to deploy Rails applications using JRuby, although he recommended to mainly use it for development and testing, but not necessarily for production. There are other tools that create a WAR file for a Rails application, which can then be deployed on any standard Java application server. I did not catch the name of the tools that Ola mentioned, but Goldspike appears to be one of them.

About 2 1/2 years ago, I prototyped a scripting engine that ran within the Java based backend for our multiplayer mobile game. At the time, I dismissed JRuby in favor of Groovy and BeanShell (we tried both to see which one we liked better), because JRuby was by far the slowest scripting language to run in Java. Today, there’s no doubt I would have strongly considered using JRuby instead.

It’s weird… somehow Java still feels like a heavyweight system to me, with its compiler, JVM, app servers, etc. But in reality, JRuby is now not only faster than the native Ruby interpreter, but also has a smaller memory footprint. And because it supports proper threads (native Java threads), you should actually have even better opportunities for optimizing the deployment of your Ruby web applications (rather than having to juggle a bunch of Mongrels…)

I will definitely have to take a closer look at JRuby and perhaps try it out with Merb. According to Ola, Merb is supported even though it does use some native C extensions. Sweet!

Update: Ola’s JRuby tech talk is on Youtube now.