#jruby_rack_worker

The title does not contain a typo, if it seems so there’s likely no need to read further. It’s actually about Resque - the Ruby library for creating background jobs using Redis. There’s been a similar post (almost 1.5 year ago!) about bringing Delayed::Job to Java. DJ evolved since and seems to be still doing fine, Resque received a fresh breeze of activity recently and the master branch shall soon spit out a new major version. Resque and Delayed::Job are different (although some points are not very accurate when comparing with DJ 3.x) yet serve usually the same purpose. And that is why the JRuby world should be able to run Resque workers threaded along side the (hopefully thread-safe) web application. Here’s how you set it up for any Servlet container running JRuby-Rack using the Java deployment descriptor : WARNING: XML ahead! // <![CDATA[ embedGist('https://gist.github.com/3986308.js?file=snippet.web.xml') // ]]> Do not forget to copy the jruby-rack-worker.jar into your WEB-INF/lib folder or declare gem 'jruby-rack-worker' in your Gemfile and Warbler should take care of it. It really should be stressed out that workers will run alongside your application and share resources such as memory, file descriptors with it thus you should not do this if your workers are expecting chaos and are not predictable (e.g. with memory consumption) or run jobs that take a long time to finish. Besides, there’s now a Trinidad extension and thus no excuse to keep on warbling forever, here’s how a the configuration file might look like : // <![CDATA[ embedGist('https://gist.github.com/3986308.js?file=trinidad.yml') // ]]>

Funny but actually true, the JVM was designed to abstract away (sometimes too much) from the OS. If you ask a Java developer to built an asynchronously worker that polls and executes new tasks as they arrive, he'll immediately write a sort of new Thread() { ... }.start() code (or he starts configuring JMS :)). The point is that Java is a notoriously Thread oriented platform. And while using JRuby on Rails you might take advantage of it while running (asynchronous) job workers. First thing you should understand is that there's a Servlet API that is the base of every Java web server you'll find (very similar to what Rack is for all Ruby servers these days). On top of it there's an adapter, most servlet containers use, when serving Rack based applications called jruby-rack. And at last, knowing all the pieces, there's jruby-rack-worker that takes some worker code and runs it in a separate thread along side your application serving requests. The only downside is that one needs to make sure the worker loop plays by the rules in a multi-thread environment. Luckily, this is fairly easy and already handled for Delayed::Job. Thus the one thing left is how to set it up, well it depends on your web server choice. You'll need to configure a listener to start the background thread when your application gets deployed, these things are usually configured in a deployment descriptor web.xml. Warbler might spill out one for you even if you do not assemble into an "universal" (.war) package. Then just add the following XML snippet to the bottom : embedGist('1056100.js'); You'll find out more in the project's README. Happy Delaying ... P.S. Just to prove a point, I've adapted Navvy as well.