Foo.rb

class Foo < Sinatra::Base

    configure do
        EM.add_periodic_timer do
            puts "hello"
        end
    end

    <other stuff>

end

Thin-Sinatra.rb

require 'foo'

EM.run do

  Thin::Logging.debug = true

  puts "Starting Thin on port #{opts[:port]}"

  map '/foo' do
    run Foo
  end


  Rack::Handler::Thin.run app, :Port => 80

end