I'm the author of cool.io and Revactor (the latter was mentioned in this article), and as much fun as it is to experiment with these ideas, the path of least surprise, especially for Rails applications, is to use threads. I wrote about that here:
Have I gotten burned by Ruby libraries that aren't thread safe? Sure. I found a thread safety bug in my application just yesterday, and it was a pain in the ass to track down. However, once I tracked it down, it was extremely easy to fix.
With JRuby (and soon with Rubinius Hydra) you can deploy one VM and take advantage of all of the CPU cores in your server. Debugging a multithreaded application isn't an impossible task, and if you're a JRuby user you have access to a whole slew of JVM tools to assist you.
http://www.unlimitednovelty.com/2010/08/multithreaded-rails-...
Have I gotten burned by Ruby libraries that aren't thread safe? Sure. I found a thread safety bug in my application just yesterday, and it was a pain in the ass to track down. However, once I tracked it down, it was extremely easy to fix.
With JRuby (and soon with Rubinius Hydra) you can deploy one VM and take advantage of all of the CPU cores in your server. Debugging a multithreaded application isn't an impossible task, and if you're a JRuby user you have access to a whole slew of JVM tools to assist you.