大資料基礎（1）zookeeper原始碼解析
五 原始碼解析
public enum ServerState {
LOOKING, FOLLOWING, LEADING, OBSERVING;
}
zookeeper伺服器狀態：剛啟動LOOKING，follower是FOLLOWING，leader是LEADING，observer是OBSERVING；
public enum LearnerType {
PARTICIPANT, OBSERVER;
}
簡單來說，zookeeper啟動的核心類是QuorumPeerMain，啟動之後會載入配置，同時啟動QuorumPeer，QuorumPeer會從本地資料目錄載入資料，然後開始選舉，選舉的核心類是FastLeaderElection，選舉完成之後會設定狀態，根據狀態的不同，啟動不同的類，比如Leader、Follower、Observer，leader會設定一個新的epoch，同時會等待follower向自己註冊，註冊完成後follower會向leader同步最新的資料，而leader則定期ping所有的follower，一旦存活的follower不足半數，leader會shutdown，然後觸發叢集的重新選舉。
具體程式碼以及呼叫如下：
org.apache.zookeeper.server.quorum.QuorumPeerMain
initializeAndRun
runFromConfig
org.apache.zookeeper.server.quorum.QuorumPeer
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