分布式ZAB协议

// 码 1 QuorumPeer.java：节点状态枚举
public enum ServerStatepublic enum ServerState {
        LOOKING,
        FOLLOWING,
        LEADING,
        OBSERVING
}

// 码 2 Vote.java：选票结构
public class Vote {
    private final int version;
    private final long id; //服务器ID
    private final long zxid; //Epoch + Counter
    private final long electionEpoch; //选举轮次
    private final long peerEpoch; //被推举的Leader所在的选举轮次
    private final ServerState state; //当前服务器状态
}

// 码 3 ZxidUtils.java：Zxid结构
public class ZxidUtils {
    public static long getEpochFromZxid(long zxid) {
        return zxid >> 32L;
    }
    public static long getCounterFromZxid(long zxid) {
        return zxid & 0xffffffffL;
    }
    public static long makeZxid(long epoch, long counter) {
        return (epoch << 32L) | (counter & 0xffffffffL);
    }
    public static String zxidToString(long zxid) {
        return Long.toHexString(zxid);
    }
}

// 码 4 FastLeaderElection.java：选票对比
protected boolean totalOrderPredicate(long newId, long newZxid, long newEpoch, long curId, long curZxid, long curEpoch) {
        LOG.debug(
            "id: {}, proposed id: {}, zxid: 0x{}, proposed zxid: 0x{}",
            newId,
            curId,
            Long.toHexString(newZxid),
            Long.toHexString(curZxid));
        if (self.getQuorumVerifier().getWeight(newId) == 0) {
            return false;
        }
        /*
         * We return true if one of the following three cases hold:
         * 1- New epoch is higher
         * 2- New epoch is the same as current epoch, but new zxid is higher
         * 3- New epoch is the same as current epoch, new zxid is the same
         * as current zxid, but server id is higher.
         */
         return ((newEpoch > curEpoch)
                || ((newEpoch == curEpoch)
                    && ((newZxid > curZxid)
                        || ((newZxid == curZxid)
                            && (newId > curId)))));
    }