Using Fibers to write linear callback code

gistfile1.rb

require 'eventmachine'
require 'em-http'
require 'fiber'

# Borrowed from http://www.igvita.com/2010/03/22/untangling-evented-code-with-ruby-fibers/

def async_fetch(url)
  # Grab a reference to which fiber I am
  f = Fiber.current

  http = EventMachine::HttpRequest.new(url).get :timeout => 10

  # The cool part - tell this fiber to resume when the HTTP callbacks happen.
  # This will start back up the fiber and continue where it left off
  http.callback { f.resume(http) }
  http.errback { f.resume(http) }

  # Pass the ball to someone else
  return Fiber.yield
end

EventMachine.run {
  # Fibers are the new hotness
  Fiber.new {
    data = async_fetch('http://ww.google.com')

    # Happens after the yield
    puts "Fetched page 1: #{data.response_header.status}"
    EventMachine.stop
  }.resume
}