How do you spawn an EventMachine “inside” a Rails app?

Question

I\'ve got a Rails application, and am looking to add some sort of WebSocket support to it. From various googling, it appears that the best Ruby based WebSocket solution is

Answer 1

You cannot run the Eventmachine engine inside of Rails itself as it is a persistent run loop that would block one of your Rails processes permanently. What is usually done is there's a side-process that uses Eventmachine and Rails communicates with it through sockets to send notifications.

Juggernaut serves as an example of this kind of thing where it implements a Websocket client and a Rails hook to send notifications to it. The project has since deprecated the Ruby version in favor of a JavaScript Node.js version but this still serves as a very thorough example of how Eventmachine can be used.

Answer 2

I had same problem and found solution. First, put your code in lib dir (for example /lib/listener/init.rb) and create one class method that run EM, for example Listener.run.

#!/usr/bin/env ruby

require File.expand_path('../../config/environment', File.dirname(__FILE__))

class Listener
  def self.run
  # your code here
  # you can access your models too
  end
end

After that I used dante gem. Create /init/listener file. The code may be like that:

#!/usr/bin/env ruby

require File.expand_path('../../lib/listener/init.rb', __FILE__)

log_file = File.expand_path('../../log/listener.stdout.log', __FILE__)
pid_file = File.expand_path('../../tmp/listener.pid', __FILE__)

listener = Dante::Runner.new('listener')

if ARGV[0] === 'start'
  listener.execute(daemonize: true,
                   pid_path: pid_file,
                   log_path: log_file) { Listener.run }
elsif ARGV[0] === 'restart'
  listener.execute(daemonize: true,
                   restart: true,
                   pid_path: pid_file,
                   log_path: log_file) { Listener.run }
elsif ARGV[0] === 'stop'
  listener.execute(kill: true, pid_path: pid_file)
end

Now you can run you code like that: ./bin/listener start, ./bin/listener restart, ./bin/listener stop

You can use god for monitoring your listener is running. But make sure you're using same pid file (/tmp/listener.pid).