Zab协议（8）-数据恢复源码分析（3）

2021SC@SDUSC

• 回顾
• 源码分析

本次继续syncWithLeader的分析

        ack.setZxid(ZxidUtils.makeZxid(newEpoch, 0));
        writePacket(ack, true);
        sock.setSoTimeout(self.tickTime * self.syncLimit);
        zk.startup();

follower发送给leader 一个ack

            qp = new QuorumPacket();
            ia.readRecord(qp, "packet");
            if(qp.getType() != Leader.ACK){
                LOG.error("Next packet was supposed to be an ACK");
                return;
            }
            LOG.info("Received NEWLEADER-ACK message from " + getSid());
            leader.waitForNewLeaderAck(getSid(), qp.getZxid());

leader 处理 发送过来的ack

    public void waitForNewLeaderAck(long sid, long zxid)
            throws InterruptedException {

        synchronized (newLeaderProposal.ackSet) {

            if (quorumFormed) {
                return;
            }

            long currentZxid = newLeaderProposal.packet.getZxid();
            if (zxid != currentZxid) {
                LOG.error("NEWLEADER ACK from sid: " + sid
                        + " is from a different epoch - current 0x"
                        + Long.toHexString(currentZxid) + " receieved 0x"
                        + Long.toHexString(zxid));
                return;
            }

            if (isParticipant(sid)) {
                newLeaderProposal.ackSet.add(sid);
            }

            if (self.getQuorumVerifier().containsQuorum(
                    newLeaderProposal.ackSet)) {
                quorumFormed = true;
                newLeaderProposal.ackSet.notifyAll();
            } else {
                long start = Time.currentElapsedTime();
                long cur = start;
                long end = start + self.getInitLimit() * self.getTickTime();
                while (!quorumFormed && cur < end) {
                    newLeaderProposal.ackSet.wait(end - cur);
                    cur = Time.currentElapsedTime();
                }
                if (!quorumFormed) {
                    throw new InterruptedException(
                            "Timeout while waiting for NEWLEADER to be acked by quorum");
                }
            }
        }
    }

利用 newLeaderProposal.ackSet.add(sid);
把发送ack的follower加入到集合中，当有超过一半的follower发送了ack之后。

            queuedPackets.add(new QuorumPacket(Leader.UPTODATE, -1, null, null));

通知follower 数据同步完毕