fibers_and_em.rb

fibers_and_em.rb

# Trying to grasp fibers and EM!
# Using this example: http://www.slideshare.net/kbal11/ruby-19-fibers (slide 54)

# Fiber#resume(*params) => when first called, it passes all params as block params to
# Fiber.new
# In the next calls of resumes, *params is the return value of any Fiber.yield

# Fiber.yield stops execution of current fiber

# So, in the run-loop from EM, the fiber stops execution and gives up control
# to EM run-loop, because of Fiber.yield in the last line of http_get. 
# The machine sits there doing nothing else (http://javieracero.com/blog/starting-with-eventmachine-i)
# When callback or errback is called, the fiber execution is resumed automatically and `http' is 
# passed as param, which is the return value of Fiber.yield, which is assigned to page and then
# the execution continues up until the next http_get, where the same logic starts to apply once again.


def http_get(url)
  f = Fiber.current
  http = EventMachine::HttpRequest.new(url).get
  
  # resume fiber once http call is done
  http.callback { f.resume(http) }
  http.errback  { f.resume(http) }
  
  return Fiber.yield
end

EventMachine.run do
  Fiber.new do
    page = http_get('http://www.google.com.br')
    puts "Fetched page: #{page.response_header.status}"
    
    page = http_get('http://www.google.com.br/search?q=eventmachine')
    puts "Fetched page: #{page.response_header.status}"
  end.resume
end