echo.rb

require 'goliath'

class Echo < Goliath::API
  use Goliath::Rack::Params
  use Goliath::Rack::Validation::RequiredParam, {:key => 'delay'}

  def response(env)
    EM::Synchrony.sleep params['delay']
    [200, {}, params['delay']]
  end
end

em.rb

require 'em-http-request'

EM.run do
  conn = EM::HttpRequest.new('http://localhost:9000/')
  start = Time.now

  r1 = conn.get :query => {delay: 1.5}, :keepalive => true
  r2 = conn.get :query => {delay: 1.0}

  r2.callback do
    p Time.now - start # =>  1.5 - keep-alive + pipelining
    EM.stop
  end
end

em2.rb

require "em-synchrony"
require "em-synchrony/em-http"
EventMachine.synchrony do
  start = Time.now
    multi = EventMachine::Synchrony::Multi.new
    multi.add :a, EventMachine::HttpRequest.new("http://localhost:9000?delay=1").aget
    multi.add :b, EventMachine::HttpRequest.new("http://localhost:9000?delay=1.5").aget
    res = multi.perform

    p "Look ma, no callbacks, and parallel HTTP requests!"
    p Time.now - start # =>  1.5 - keep-alive + pipelining

    EventMachine.stop
end