'Gets the next tracker for automatic tracker-checking.
:return: The next tracker for automatic tracker-checking.'

@call_on_reactor_thread
def get_next_tracker_for_auto_check(self):

    if (len(self._tracker_dict) == 0):
        return
    next_tracker_url = None
    next_tracker_info = None
    sorted_tracker_list = sorted(self._tracker_dict.items(), key=(lambda d: d[1][u'last_check']))
    for (tracker_url, tracker_info) in sorted_tracker_list:
        if (tracker_url == u'DHT'):
            next_tracker_url = tracker_url
            next_tracker_info = {u'is_alive': True, u'last_check': int(time.time())}
            break
        elif ((tracker_url != u'no-DHT') and self.should_check_tracker(tracker_url)):
            next_tracker_url = tracker_url
            next_tracker_info = tracker_info
            break
    if (next_tracker_url is None):
        return
    return (next_tracker_url, next_tracker_info)
