选举结束后，leader 和 follower 各自执行自己的逻辑：
org.apache.zookeeper.server.quorum.QuorumPeer#run
leader
org.apache.zookeeper.server.quorum.QuorumPeer#setLeader // 构建 processor 链 org.apache.zookeeper.server.quorum.LeaderZooKeeperServer#setupRequestProcessors // PrepRequestProcessor, ProposalRequestProcessor, CommitProcessor, ToBeAppliedRequestProcessor, FinalRequestProcessor org.apache.zookeeper.server.quorum.Leader#lead
follower
org.apache.zookeeper.server.quorum.QuorumPeer#setFollower // 构建 processor 链 org.apache.zookeeper.server.quorum.FollowerZooKeeperServer#setupRequestProcessors // 链1：FollowerRequestProcessor, CommitProcessor, FinalRequestProcessor // 链2：SyncRequestProcessor, SendAckRequestProcessor org.apache.zookeeper.server.quorum.Follower#followLeader
leader 发送建议给 follower
org.apache.zookeeper.server.quorum.LearnerHandler#sendPackets
follower 接收并处理 leader 发送的建议
org.apache.zookeeper.server.quorum.Follower#processPacket
// SyncRequestProcessor 写入事务日志 org.apache.zookeeper.server.SyncRequestProcessor#run // 发送 ACK 给 leader org.apache.zookeeper.server.quorum.SendAckRequestProcessor#processRequest
leader 接收并处理 follower 的请求
org.apache.zookeeper.server.quorum.LearnerHandler#run // ack 超过半数，则把写操作应用到状态机，并向 follower 发送提交事件 org.apache.zookeeper.server.quorum.Leader#processAck
follower 提交写操作
CommitProcessor 和 FinalRequestProcessor