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raft.go
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raft.go
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package raft
//
// this is an outline of the API that raft must expose to
// the service (or tester). see comments below for
// each of these functions for more details.
//
// rf = Make(...)
// create a new Raft server.
// rf.Start(command interface{}) (index, term, isleader)
// start agreement on a new log entry
// rf.GetState() (term, isLeader)
// ask a Raft for its current term, and whether it thinks it is leader
// ApplyMsg
// each time a new entry is committed to the log, each Raft peer
// should send an ApplyMsg to the service (or tester)
// in the same server.
//
import "sync"
import "sync/atomic"
import "../labrpc"
// import "bytes"
// import "../labgob"
//
// as each Raft peer becomes aware that successive log entries are
// committed, the peer should send an ApplyMsg to the service (or
// tester) on the same server, via the applyCh passed to Make(). set
// CommandValid to true to indicate that the ApplyMsg contains a newly
// committed log entry.
//
// in Lab 3 you'll want to send other kinds of messages (e.g.,
// snapshots) on the applyCh; at that point you can add fields to
// ApplyMsg, but set CommandValid to false for these other uses.
//
type ApplyMsg struct {
CommandValid bool
Command interface{}
CommandIndex int
}
//
// A Go object implementing a single Raft peer.
//
type Raft struct {
mu sync.Mutex // Lock to protect shared access to this peer's state
peers []*labrpc.ClientEnd // RPC end points of all peers
persister *Persister // Object to hold this peer's persisted state
me int // this peer's index into peers[]
dead int32 // set by Kill()
// Your data here (2A, 2B, 2C).
// Look at the paper's Figure 2 for a description of what
// state a Raft server must maintain.
}
// return currentTerm and whether this server
// believes it is the leader.
func (rf *Raft) GetState() (int, bool) {
var term int
var isleader bool
// Your code here (2A).
return term, isleader
}
//
// save Raft's persistent state to stable storage,
// where it can later be retrieved after a crash and restart.
// see paper's Figure 2 for a description of what should be persistent.
//
func (rf *Raft) persist() {
// Your code here (2C).
// Example:
// w := new(bytes.Buffer)
// e := labgob.NewEncoder(w)
// e.Encode(rf.xxx)
// e.Encode(rf.yyy)
// data := w.Bytes()
// rf.persister.SaveRaftState(data)
}
//
// restore previously persisted state.
//
func (rf *Raft) readPersist(data []byte) {
if data == nil || len(data) < 1 { // bootstrap without any state?
return
}
// Your code here (2C).
// Example:
// r := bytes.NewBuffer(data)
// d := labgob.NewDecoder(r)
// var xxx
// var yyy
// if d.Decode(&xxx) != nil ||
// d.Decode(&yyy) != nil {
// error...
// } else {
// rf.xxx = xxx
// rf.yyy = yyy
// }
}
//
// example RequestVote RPC arguments structure.
// field names must start with capital letters!
//
type RequestVoteArgs struct {
// Your data here (2A, 2B).
}
//
// example RequestVote RPC reply structure.
// field names must start with capital letters!
//
type RequestVoteReply struct {
// Your data here (2A).
}
//
// example RequestVote RPC handler.
//
func (rf *Raft) RequestVote(args *RequestVoteArgs, reply *RequestVoteReply) {
// Your code here (2A, 2B).
}
//
// 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 *reply with RPC reply, so caller should
// pass &reply.
// the types of the args and reply passed to Call() must be
// the same as the types of the arguments declared in the
// handler function (including whether they are pointers).
//
// The labrpc package simulates a lossy network, in which servers
// may be unreachable, and in which requests and replies may be lost.
// Call() sends a request and waits for a reply. If a reply arrives
// within a timeout interval, Call() returns true; otherwise
// Call() returns false. Thus Call() may not return for a while.
// A false return can be caused by a dead server, a live server that
// can't be reached, a lost request, or a lost reply.
//
// Call() is guaranteed to return (perhaps after a delay) *except* if the
// handler function on the server side does not return. Thus there
// is no need to implement your own timeouts around Call().
//
// look at the comments in ../labrpc/labrpc.go for more details.
//
// if you're having trouble getting RPC to work, check that you've
// capitalized all field names in structs passed over RPC, and
// that the caller passes the address of the reply struct with &, not
// the struct itself.
//
func (rf *Raft) sendRequestVote(server int, args *RequestVoteArgs, reply *RequestVoteReply) bool {
ok := rf.peers[server].Call("Raft.RequestVote", args, reply)
return ok
}
//
// the service using Raft (e.g. a k/v server) wants to start
// agreement on the next command to be appended to Raft's log. if this
// server isn't the leader, returns false. otherwise start the
// agreement and return immediately. there is no guarantee that this
// command will ever be committed to the Raft log, since the leader
// may fail or lose an election. even if the Raft instance has been killed,
// this function should return gracefully.
//
// the first return value is the index that the command will appear at
// if it's ever committed. the second return value is the current
// term. the third return value is true if this server believes it is
// the leader.
//
func (rf *Raft) Start(command interface{}) (int, int, bool) {
index := -1
term := -1
isLeader := true
// Your code here (2B).
return index, term, isLeader
}
//
// the tester doesn't halt goroutines created by Raft after each test,
// but it does call the Kill() method. your code can use killed() to
// check whether Kill() has been called. the use of atomic avoids the
// need for a lock.
//
// the issue is that long-running goroutines use memory and may chew
// up CPU time, perhaps causing later tests to fail and generating
// confusing debug output. any goroutine with a long-running loop
// should call killed() to check whether it should stop.
//
func (rf *Raft) Kill() {
atomic.StoreInt32(&rf.dead, 1)
// Your code here, if desired.
}
func (rf *Raft) killed() bool {
z := atomic.LoadInt32(&rf.dead)
return z == 1
}
//
// the service or tester wants to create a Raft server. the ports
// of all the Raft servers (including this one) are in peers[]. this
// server's port is peers[me]. all the servers' peers[] arrays
// have the same order. persister is a place for this server to
// save its persistent state, and also initially holds the most
// recent saved state, if any. applyCh is a channel on which the
// tester or service expects Raft to send ApplyMsg messages.
// Make() must return quickly, so it should start goroutines
// for any long-running work.
//
func Make(peers []*labrpc.ClientEnd, me int,
persister *Persister, applyCh chan ApplyMsg) *Raft {
rf := &Raft{}
rf.peers = peers
rf.persister = persister
rf.me = me
// Your initialization code here (2A, 2B, 2C).
// initialize from state persisted before a crash
rf.readPersist(persister.ReadRaftState())
return rf
}