7、zk源码阅读--选举后不同角色之间的操作

case FOLLOWING:
    try {
        LOG.info("FOLLOWING");
        setFollower(makeFollower(logFactory));
        follower.followLeader();
    } catch (Exception e) {
        LOG.warn("Unexpected exception", e);
    } finally {
        follower.shutdown();
        setFollower(null);
        updateServerState();
    }
    break;
case LEADING:
    LOG.info("LEADING");
    try {
        setLeader(makeLeader(logFactory));
        leader.lead();
        setLeader(null);
    } catch (Exception e) {
        LOG.warn("Unexpected exception", e);
    } finally {
        if (leader != null) {
            leader.shutdown("Forcing shutdown");
            setLeader(null);
        }
        updateServerState();
    }     上一篇讲到进行了选举结束，那么每个节点的角色会确定，这一篇，看看follower和leader角色分别会做什么操作，先看leader

如果该服务器是leader角色，那么会调用makeLeader方法，这个方法里会new Leader，直接看Leader的构造函数

   public Leader(QuorumPeer self, LeaderZooKeeperServer zk) throws IOException {
        this.self = self;
        this.proposalStats = new BufferStats();

        Set<InetSocketAddress> addresses;
        if (self.getQuorumListenOnAllIPs()) {
            addresses = self.getQuorumAddress().getWildcardAddresses();
        } else {
            addresses = self.getQuorumAddress().getAllAddresses();
        }

        addresses.stream()
          .map(address -> createServerSocket(address, self.shouldUsePortUnification(), self.isSslQuorum()))
          .filter(Optional::isPresent)
          .map(Optional::get)
          .forEach(serverSockets::add);

        if (serverSockets.isEmpty()) {
            throw new IOException("Leader failed to initialize any of the following sockets: " + addresses);
        }

        this.zk = zk;
    }

可以看到这里是为每个ip创建ServerSocket，由此我们可以知道服务端之间的通讯是走的BIO。为什么这里走bio呢，因为zk服务端不多呀，撑死一个集群就10台-30台服务器吧，用bio处理是够用了。

创建好所有的ServerSocket后会调用lead方法，lead方法里面履行的是leader的职责，这里代码挺多的，总结一下，这坨代码做了以下几件事情。

1、zk.loadData()

2、开始LearnCnxAcceptor线程

3、设置一通QuorumVerifier（妈呀，这个玩意是干嘛的）

4、等待其他节点选举的ack

5、startZkServer()

6、上报心跳

这6个步骤里面最重要的是LearnCnxAcceptor线程了，我们来看看里面做的是什么操作

顾名思义，这个线程事接收follower节点请求的。

public void run() {
                try {
                    Thread.currentThread().setName("LearnerCnxAcceptorHandler-" + serverSocket.getLocalSocketAddress());

                    while (!stop.get()) {
                        acceptConnections();
                    }
                } catch (Exception e) {
                    LOG.warn("Exception while accepting follower", e);
                    if (fail.compareAndSet(false, true)) {
                        handleException(getName(), e);
                        halt();
                    }
                } finally {
                    latch.countDown();
                }
            }

private void acceptConnections() throws IOException {
                Socket socket = null;
                boolean error = false;
                try {
                    socket = serverSocket.accept();

                    // start with the initLimit, once the ack is processed
                    // in LearnerHandler switch to the syncLimit
                    socket.setSoTimeout(self.tickTime * self.initLimit);
                    socket.setTcpNoDelay(nodelay);

                    BufferedInputStream is = new BufferedInputStream(socket.getInputStream());
                    LearnerHandler fh = new LearnerHandler(socket, i