<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_feedback(self, block = True, timeout = None):
 		""" 		Gets the next feedback message. 		Each feedback message is a 2-tuple of (timestamp, device_token)."""

		if self._feedback_greenlet is None:
			self._feedback_greenlet = gevent.spawn(self._feedback_loop)
		return self._feedback_queue.get(block = block, timeout = timeout)