paxos-register-acceptor.py

Accepted = namedtuple('Accepted', ['n', 'val'])
class Register:
    def __init__(self, nodes, q):
        self.q = q           # quorum size
        self.nodes = nodes   # addresses of all nodes (including current)
        self.promise = -1    # promise
        self.accepted = None # accepted pair of a value and its ballot num
        self.chosen = None   # stores cached chosen value
    @synchronized
    def prepare(self, n):
        if self.promise < n:
            self.promise = n
            return self.accepted
        return Conflict(promise=self.promise)
    @synchronized
    def accept(self, n, val):
        if self.promise == n:
            self.accepted = Accepted(n, val)
            return OK()
        return Conflict(promise=self.promise)
    @synchronized
    def choose(self, val):
        self.chosen = val