code: def __watchers_callbacks_exec(self, signal_name):
  		
  		def callback_fn():
  			for watcher in self.__watchers_callbacks[signal_name]:
  				if watcher is not None:
  					watcher.notify()
  		return callback_fn
docs: Generate callback for a queue
  
  		:param signal_name: name of a signal that callback is generated for
  		:type signal_name: str
  
  		:rtype: callable