// handleFollowers ensures that followers are informed
// about new messages and lagging followers catch up
// AppendEntry and AppendEntryResponses occur in
// lockstep. aeToken is used to implement mutex like
// behaviour to ensure that a new AppendEntry message
// is sent only when response to previous AppendEntry
// message is received
func (s *raftServer) handleFollowers(followers []int, nextIndex *utils.SyncIntIntMap, matchIndex *utils.SyncIntIntMap, aeToken *utils.SyncIntIntMap) {
for s.State() == LEADER {
for _, f := range followers {
lastIndex := s.localLog.TailIndex()
n, ok := nextIndex.Get(f)
if !ok {
panic("nextIndex not found for follower " + strconv.Itoa(f))
}
unlocked, ok := aeToken.Get(f)
if !ok {
panic("aeToken not found for follower " + strconv.Itoa(f))
}
if lastIndex != 0 && lastIndex >= n && unlocked == 1 {
aeToken.Set(f, 0)
// send a new AppendEntry
prevIndex := n - 1
var prevTerm int64 = 0
// n = 0 when we add first entry to the log
if prevIndex > 0 {
prevTerm = s.localLog.Get(prevIndex).Term
}
ae := &AppendEntry{Term: s.Term(), LeaderId: s.server.Pid(), PrevLogIndex: prevIndex, PrevLogTerm: prevTerm}
ae.LeaderCommit = s.commitIndex.Get()
ae.Entry = *s.localLog.Get(n)
s.writeToLog("Replicating entry " + strconv.FormatInt(n, 10))
s.server.Outbox() <- &cluster.Envelope{Pid: f, Msg: ae}
}
}
time.Sleep(NICE * time.Millisecond)
}
}
// respondToClient replies to the client when
// an entry is replicated on majority of servers
func (s *raftServer) updateLeaderCommitIndex(followers []int, matchIndex *utils.SyncIntIntMap) {
for s.State() == LEADER {
N := s.commitIndex.Get() + 1
upto := N + 1
for N <= upto {
if !s.localLog.Exists(N) {
break
}
i := 1
for _, f := range followers {
if j, _ := matchIndex.Get(f); j >= N {
i++
upto = max(upto, j)
}
}
// followers do not include Leader
if entry := s.localLog.Get(N); i > (len(followers)+1)/2 && entry.Term == s.Term() {
s.writeToLog("Updating commitIndex to " + strconv.FormatInt(N, 10))
s.commitIndex.Set(N)
}
N++
}
time.Sleep(NICE * time.Millisecond)
}
}