系列文章目录

【zookeeper核心源码解析】第一课：zk启动类核心流程序列图
【zookeeper核心源码解析】第二课：俯瞰QuorumPeer启动核心流程，实现选举关键流程
【zookeeper核心源码解析】第三课：leader与follower何时开始同步，如何同步数据
【zookeeper核心源码解析】第四课：客户端与服务端读写的io核心流程

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1. QuorumPeer.run() 核心流程执行流程进行选举（选举过程与结果）

 @Overridepublic void run() {setName("QuorumPeer" + "[myid=" + getId() + "]" +cnxnFactory.getLocalAddress());LOG.debug("Starting quorum peer");try {jmxQuorumBean = new QuorumBean(this);MBeanRegistry.getInstance().register(jmxQuorumBean, null);for(QuorumServer s: getView().values()){ZKMBeanInfo p;if (getId() == s.id) {p = jmxLocalPeerBean = new LocalPeerBean(this);try {MBeanRegistry.getInstance().register(p, jmxQuorumBean);} catch (Exception e) {LOG.warn("Failed to register with JMX", e);jmxLocalPeerBean = null;}} else {p = new RemotePeerBean(s);try {MBeanRegistry.getInstance().register(p, jmxQuorumBean);} catch (Exception e) {LOG.warn("Failed to register with JMX", e);}}}} catch (Exception e) {LOG.warn("Failed to register with JMX", e);jmxQuorumBean = null;}try {/** Main loop*/while (running) {switch (getPeerState()) {case LOOKING:LOG.info("LOOKING");if (Boolean.getBoolean("readonlymode.enabled")) {LOG.info("Attempting to start ReadOnlyZooKeeperServer");// Create read-only server but don't start it immediatelyfinal ReadOnlyZooKeeperServer roZk = new ReadOnlyZooKeeperServer(logFactory, this,new ZooKeeperServer.BasicDataTreeBuilder(),this.zkDb);// Instead of starting roZk immediately, wait some grace// period before we decide we're partitioned.//// Thread is used here because otherwise it would require// changes in each of election strategy classes which is// unnecessary code coupling.Thread roZkMgr = new Thread() {public void run() {try {// lower-bound grace period to 2 secssleep(Math.max(2000, tickTime));if (ServerState.LOOKING.equals(getPeerState())) {roZk.startup();}} catch (InterruptedException e) {LOG.info("Interrupted while attempting to start ReadOnlyZooKeeperServer, not started");} catch (Exception e) {LOG.error("FAILED to start ReadOnlyZooKeeperServer", e);}}};try {roZkMgr.start();setCurrentVote(makeLEStrategy().lookForLeader());} catch (Exception e) {LOG.warn("Unexpected exception",e);setPeerState(ServerState.LOOKING);} finally {// If the thread is in the the grace period, interrupt// to come out of waiting.roZkMgr.interrupt();roZk.shutdown();}} else {try {setCurrentVote(makeLEStrategy().lookForLeader());} catch (Exception e) {LOG.warn("Unexpected exception", e);setPeerState(ServerState.LOOKING);}}break;case OBSERVING:try {LOG.info("OBSERVING");setObserver(makeObserver(logFactory));observer.observeLeader();} catch (Exception e) {LOG.warn("Unexpected exception",e );                        } finally {observer.shutdown();setObserver(null);setPeerState(ServerState.LOOKING);}break;case FOLLOWING:try {LOG.info("FOLLOWING");setFollower(makeFollower(logFactory));follower.followLeader();} catch (Exception e) {LOG.warn("Unexpected exception",e);} finally {follower.shutdown();setFollower(null);setPeerState(ServerState.LOOKING);}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);}setPeerState(ServerState.LOOKING);}break;}}} finally {LOG.warn("QuorumPeer main thread exited");try {MBeanRegistry.getInstance().unregisterAll();} catch (Exception e) {LOG.warn("Failed to unregister with JMX", e);}jmxQuorumBean = null;jmxLocalPeerBean = null;}}

2. run方法解释

1.选举状态有四种，一种是LOOKING，FOLLOWING，LEADING，OBSERVING
2. 一开始是Looking状态，进行选举，选举结束后，才决定leader和follower,分别创建leader和follower对象，并执行leader.lead()， follower.followLeader() 的方式，这时，完成leader和follower进程启动