大数据基础之Zookeeper（2）源代码解析

核心枚举

public enum ServerState {
    LOOKING, FOLLOWING, LEADING, OBSERVING;
}

zookeeper服务器状态：刚启动LOOKING，follower是FOLLOWING，leader是LEADING，observer是OBSERVING；

public enum LearnerType {
    PARTICIPANT, OBSERVER;
}

简单来说，zookeeper启动的核心类是QuorumPeerMain，启动之后会加载配置，同时启动QuorumPeer，QuorumPeer会从本地数据目录加载数据，然后开始选举，选举的核心类是FastLeaderElection，选举完成之后会设置状态，根据状态的不同，启动不同的类，比如Leader、Follower、Observer，leader会设置一个新的epoch，同时会等待follower向自己注册，注册完成后follower会向leader同步最新的数据，而leader则定期ping所有的follower，一旦存活的follower不足半数，leader会shutdown，然后触发集群的重新选举。

具体代码以及调用如下：

org.apache.zookeeper.server.quorum.QuorumPeerMain

         initializeAndRun

                  runFromConfig

                          org.apache.zookeeper.server.quorum.QuorumPeer extends ZooKeeperThread

                                   initialize

                                   start

                                            loadDataBase

                                            org.apache.zookeeper.server.ServerCnxnFactory

                                                     start

                                            startLeaderElection

                                                     org.apache.zookeeper.server.quorum.QuorumPeer.ResponderThread

                                                             start

                                                     createElectionAlgorithm

                                            run

                                                     org.apache.zookeeper.server.quorum.FastLeaderElection implements Election

                                                             lookForLeader

                                                                      sendNotifications

                                                                      totalOrderPredicate

                                                                      termPredicate

                                                                               org.apache.zookeeper.server.quorum.flexible.QuorumMaj

                                                                                        containsQuorum

                                                                      QuorumPeer.setPeerState

                                                             1 org.apache.zookeeper.server.quorum.Leader extends Learner

                                                                      lead

                                                                               org.apache.zookeeper.server.quorum.Leader.LearnerCnxAcceptor extends ZooKeeperThread

                                                                                        run

                                                                                                 org.apache.zookeeper.server.quorum.LearnerHandler extends ZooKeeperThread

                                                                                                         start

                                                                                                                  receive Leader.FOLLOWERINFO

                                                                               epoch++

                                                                               setZxid

                                                                               setCurrentEpoch

                                                                               waitForNewLeaderAck

                                                                               startZkServer

                                                                               loop

                                                                                        org.apache.zookeeper.server.quorum.LearnerHandler

                                                                                                ping

                                                                                                         org.apache.zookeeper.server.quorum.LearnerHandler.SyncLimitCheck

                                                                                                                  check

                                                                                                         shutdown

                                                                                                                  Leader.removeLearnerHandler

                                                                                        containsQuorum

                                                                                        shutdown

                                                             2 org.apache.zookeeper.server.quorum.Follower extends Learner

                                                                      followLeader

                                                                               findLeader

                                                                               connectToLeader

                                                                               registerWithLeader

                                                                                        send Leader.FOLLOWERINFO

                                                                               syncWithLeader

                                                             3 org.apache.zookeeper.server.quorum.Observer extends Learner

                                                                      observeLeader

选举代码解析请见  大数据基础之Zookeeper（3）选举算法