Ruby Sinatra web apps with background work threads

In Java-land, I have often used the pattern of writing a servlet with an init() method that starts up one or more background work threads. Then while my web application is handling HTTP requests the background threads can be doing work like fetching RSS feeds for display in the web app, perform periodic maintenance like flushing old data from a database, etc. This is a simple pattern that is robust and easy to implement with a few extra lines of Java code and an extra servlet definition in a web.xml file.

In Ruby-land this pattern is even simpler to implement:

require 'rubygems'
require 'sinatra'

$sum = 0

Thread.new do # trivial example work thread
  while true do
     sleep 0.12
     $sum += 1
  end
end

get '/' do
  "Testing background work thread: sum is #{$sum}"
end

While the main thread is waiting for HTTP requests the background thread can do any other work. This works fine with Ruby 1.8.7 or any 1.9.*, but I would run this in JRuby for a long-running production app since JRuby uses the Java Thread class.