Raft Lab 2

The Raft Interface

先bb一下：要implement任何东西，都必须先搞清楚它的interface。在实际开发中和客户交流基本上就是决定一个合理的interface。

func Make(peers []*labrpc.ClientEnd, me int, persister *Persister, applyCh chan ApplyMsg) *Raft

Make()创建一个新的raft peer(服务器)。

func (rf *Raft) Start(command interface{}) (int, int, bool)

服务（比如kv server）调用Start(command)来新建一个command。

rf.GetState() (term, isLeader)

ask a Raft for its current term, and whether it thinks it is leader

ApplyMsg struct
applyCh chan

Each time a new entry is committed to the log, each Raft peer should send an ApplyMsg to the service in the same server. 顾名思义，这个message就是和上层服务说：我log已经committed了，你可以安全地把log里面的command给apply掉。

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