gistfile1.txt

class ResponseHandler:
  def __init__(callback):
    self.counter = 0
    self.callback = callback

  def start:
    self.counter += 1 # lock

  def _on_response:
    self.counter -= 1
    if self.counter == 0:
      self.callback()

  def add_call(url):
    self.counter += 1
    fetch(url, self._on_response)

  def end:
    self.counter -= 1
    if self.counter == 0:
      self.callback()



rh = ResponseHandler(mycallback)
rh.start()
rh.add_call(myurl1)
rh.add_call(myurl2)
rh.add_call(myurl3)
rh.end()