+
+ # We assign each servers/trackers into one three lists. They all
+ # start in the "first pass" list. During the first pass, as we ask
+ # each one to hold a share, we move their tracker to the "second
+ # pass" list, until the first-pass list is empty. Then during the
+ # second pass, as we ask each to hold more shares, we move their
+ # tracker to the "next pass" list, until the second-pass list is
+ # empty. Then we move everybody from the next-pass list back to the
+ # second-pass list and repeat the "second" pass (really the third,
+ # fourth, etc pass), until all shares are assigned, or we've run out
+ # of potential servers.
+ self.first_pass_trackers = _make_trackers(writable_servers)
+ self.second_pass_trackers = [] # servers worth asking again
+ self.next_pass_trackers = [] # servers that we have asked again
+ self._started_second_pass = False