每当 rf.logs 或 rf.commitIndex 有变化时，就收到通知 然后，检查发现有可以 commit 的 entry 的话 就通过 applyCh 发送 ApplyMsg 给 replication state machine 进行 commit

check that for a specific client all known appends are present in a value, and in order

check that all known appends are present in a value, and are in order for each concurrent client.

warn if the value contains non-default values, as it would if one sent an RPC but the reply struct was already modified. if the RPC reply contains de

check that there's no leader

触发 election timer 超时，就开始新的选举

helper function that sends information about all existing and newly registered workers to channel ch. schedule() reads ch to learn about workers.

killWorkers cleans up all workers by sending each one a Shutdown RPC. It also collects and returns the number of tasks each worker has performed.

创建 *fetchState 实体

Partition servers into 2 groups and put current leader in minority

The map function is called once for each file of input. The first argument is the name of the input file, and the second is the file's complete conte

master 负责分配爬取任务给 worker

merge combines the results of the many reduce jobs into a single output file XXX use merge sort

data layout: bits 0-63 are in data[0], the next are in data[1], etc.

往服务器存放数据 (key, val)

Randomize server handles

Randomize server handles

The reduce function is called once for each key generated by the map tasks, with a list of all the values created for that key by any map task.

Tell the master we exist and ready to work

a client runs the function f and then signals it is done

example code to send a RequestVote RPC to a server. server is the index of the target server in rf.peers[]. expects RPC arguments in args. fills in *

启动服务器

startRPCServer starts the Master's RPC server. It continues accepting RPC calls (Register in particular) for as long as the worker is alive.

stopRPCServer stops the master RPC server. This must be done through an RPC to avoid race conditions between the RPC server thread and the current thr