paxos-variable-heart.py

    def _read_write_read(self, test, val, due):
        n = self._get_n(0)
        resps = net.send(self.nodes, lambda x: x.prepare(n), due-now())
        try:
            # Waiting for q (majority) succeeded responses.
            ok = resps.where(lambda x: isinstance(x.msg, Accepted)).wait(self.q)
            last = ok.max(lambda x: x.msg.n).msg.val
            if test != None and test(last):
                candidate = val
            else:
                candidate = last
            acks = net.send(ok.nodes, lambda x: x.accept(n, candidate), due-now())
            resps += acks
            acks.where(lambda x: isinstance(x.msg, OK)).wait(self.q)
            if test != None and not test(last): return Conflict(val=last)
            return OK(val=candidate)
        except CantResolveWait:
            return NetworkError()
        finally:
            resps = resps.abort() # abort the connections and
            # pick a ballot number greater than any of already known
            for x in resps.where(lambda x: isinstance(x.msg, Conflict)):
                self._get_n(x.msg.promise)