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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).
//
// 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 (
// "bytes"
"bytes"
"fmt"
"math/rand"
"os"
"sync"
"sync/atomic"
"time"
"encoding/gob"
"net/rpc"
"github.com/fatih/color"
)
// 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.
type ApplyMsg struct {
CommandValid bool
Command interface{}
CommandIndex int
SnapshotValid bool
Snapshot []byte
SnapshotTerm int
SnapshotIndex 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 []*rpc.Client // 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()
// state a Raft server must maintain.
//extra state that i find helpful to keep
last_heard int64
my_election_Time int64
waitingToCommit int32
isLeader bool
commitChannel chan bool //channel to wait on for new index to commit
state string // follower | candidate leader
vote Vote
applyChannel chan ApplyMsg
// Persistent state on all
currentTerm int // Last term server has seen, increased by elections
log map[int]LogEntry // commands for state machine
logMutex sync.Mutex // lock to protect acces to log
//& term when entry was received by leader, starts at 1
// Volatile state on all
commitIndex int // Index of highest log entry known to be commited, initialized to 0, incr mono
lastApplied int // Index of highest log entry applied to state machine, initialized to 0, incr mono
// Volatile state on leader (reinitialized after election)
replicatedCnt map[int]int // how many servers replicated log entry
replicaMutex sync.Mutex // lock to protect acces to replicatedCnt
nextIndex []int //for each server, index of the next log entry to send to that server init to last log index +1
matchIndex []int //for each server, index of highest log entry known to be replicated on server
// initialized to 0, increases monotonically
}
func (rf *Raft) Kill() {
//free routines from waiting on lock
atomic.StoreInt32(&rf.dead, 1)
go notifyChannel(&rf.commitChannel, &rf.waitingToCommit)
}
func (rf *Raft) killed() bool {
z := atomic.LoadInt32(&rf.dead)
return z == 1
}
// use as separate go routine when you need to notify on channel without blocking function
func notifyChannel(channel *chan bool, busy *int32) {
if atomic.LoadInt32(busy) == 0 {
atomic.StoreInt32(busy, 1)
*channel <- true
atomic.StoreInt32(busy, 0)
}
}
// for logging
func writeToFile(fname string, log string) {
f, err := os.OpenFile(fname,
os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
if err != nil {
println(err)
}
defer f.Close()
if _, err := f.WriteString(log); err != nil {
println(err)
}
}
// return currentTerm and whether this server
// believes it is the leader.
func (rf *Raft) GetState() (int, bool) {
return rf.currentTerm, rf.isLeader
}
func (rf *Raft) PrintLog() {
color.Blue("Server: %v\n", rf.me)
for index := 1; index <= len(rf.log); index++ {
color.Blue("MY TERM : %v|INDEX: %v, COMMAND: %v TERM: %v| COMMIT_INDEX: %v|", rf.currentTerm, index, rf.log[index].Command, rf.log[index].Term, rf.commitIndex)
}
color.Blue("\n")
}
// 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() {
w := new(bytes.Buffer)
e := gob.NewEncoder(w)
rf.mu.Lock()
e.Encode(rf.currentTerm)
e.Encode(rf.vote)
rf.mu.Unlock()
rf.logMutex.Lock()
e.Encode(rf.log)
rf.logMutex.Unlock()
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
}
r := bytes.NewBuffer(data)
d := gob.NewDecoder(r)
currentTerm := 0
votedFor := (Vote{})
log := (map[int]LogEntry{})
err := d.Decode(¤tTerm)
if err != nil {
fmt.Println(err)
return
}
err = d.Decode(&votedFor)
if err != nil {
fmt.Println(err)
return
}
err = d.Decode(&log)
if err != nil {
fmt.Println(err)
return
}
rf.mu.Lock()
rf.currentTerm = currentTerm
rf.vote = votedFor
rf.log = log
rf.mu.Unlock()
}
// A service wants to switch to snapshot. Only do so if Raft hasn't
// have more recent info since it communicate the snapshot on applyCh.
func (rf *Raft) CondInstallSnapshot(lastIncludedTerm int, lastIncludedIndex int, snapshot []byte) bool {
return true
}
// the service says it has created a snapshot that has
// all info up to and including index. this means the
// service no longer needs the log through (and including)
// that index. Raft should now trim its log as much as possible.
func (rf *Raft) Snapshot(index int, snapshot []byte) {
}
func (rf *Raft) commit(from int, to int) {
rf.logMutex.Lock()
for i := from + 1; i <= to; i++ {
command := rf.log[i].Command
rf.applyChannel <- ApplyMsg{CommandValid: true, Command: command, CommandIndex: i}
}
rf.logMutex.Unlock()
}
func (rf *Raft) CommitController() {
prevcommitIndex := rf.commitIndex
for !rf.killed() {
if rf.isLeader {
for i := len(rf.log); i > prevcommitIndex; i-- {
rf.replicaMutex.Lock()
iCount := rf.replicatedCnt[i]
rf.replicaMutex.Unlock()
rf.logMutex.Lock()
iTerm := rf.log[i].Term
rf.logMutex.Unlock()
if iCount > len(rf.peers)/2 && iTerm == rf.currentTerm {
rf.mu.Lock()
rf.commitIndex = i
rf.mu.Unlock()
break
}
}
}
if (!rf.isLeader && rf.commitIndex > prevcommitIndex) || rf.isLeader {
rf.mu.Lock()
rf.commit(prevcommitIndex, rf.commitIndex)
prevcommitIndex = rf.commitIndex
rf.mu.Unlock()
<-rf.commitChannel
}
}
}
// 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) {
// idk raft paper suggest sending valid leader in that case
if !rf.isLeader {
return -1, -1, false
}
//46:56 check if command already in log
rf.logMutex.Lock()
for idx, entry := range rf.log {
if entry.Command == command {
rf.logMutex.Unlock()
return idx, entry.Term, true
}
}
newEntry := LogEntry{Command: command, Term: rf.currentTerm}
// TODO write to its own log and update state
index := len(rf.log) + 1
//rf.logMutex.Unlock()
rf.replicaMutex.Lock()
rf.replicatedCnt[index] = 1
rf.replicaMutex.Unlock()
// rf.logMutex.Lock()
rf.log[index] = newEntry
rf.logMutex.Unlock()
rf.persist()
return index, rf.currentTerm, true
}
// Make() must return quickly, so it should start goroutines
// for any long-running work.
func Make(peers []*rpc.Client, me int,
persister *Persister, applyCh chan ApplyMsg) *Raft {
rf := &Raft{}
rf.peers = peers
rf.persister = persister
rf.me = me
rf.isLeader = false
rf.my_election_Time = rand.Int63n(electionTimeHigh-electionTimeLow) + electionTimeLow
rf.last_heard = time.Now().UnixMilli()
rf.state = Follower
//create buffered channel
rf.commitChannel = make(chan bool, 1)
rf.waitingToCommit = 0
rf.currentTerm = 0
rf.vote = Vote{Votedfor: -1, VotedTerm: -1}
rf.applyChannel = applyCh
rf.log = make(map[int]LogEntry)
rf.commitIndex = 0
rf.lastApplied = 0
rf.replicatedCnt = make(map[int]int)
rf.nextIndex = make([]int, len(rf.peers))
for i := range rf.nextIndex {
rf.nextIndex[i] = 1
}
rf.matchIndex = make([]int, len(rf.peers))
for i := range rf.matchIndex {
rf.matchIndex[i] = 0
}
// initialize from state persisted before a crash
rf.readPersist(persister.ReadRaftState())
// start ticker goroutine to start elections
go rf.ticker()
go rf.CommitController()
return rf
}