// ElectLeader performs a leader election for the next round.
func (this *Election) ElectLeader(timeout time.Duration) (
string, int64, error) {
lock := this.ctlr.ReadLockAll()
target := this.msn.UID()
if !this.InCommittee() {
target = this.committee[rand.Intn(len(this.committee))]
}
lock.Unlock()
request := thispb.ElectRequest{}
request.ElectionRound = proto.Int64(this.CurrentRound() + 1)
message := thispb.ElectionMessage{}
message.ElectRequest = &request
reqHeader := this.msn.NewRequest(this.namespace, this.uid, "Election.Elect",
timeout)
defer this.msn.CloseMessage(reqHeader)
if err := msg.SendProto(this.msn, target, reqHeader, &message); err != nil {
this.Errorf("could not send elect request to %s: %v", target, err)
return "", -1, err
}
message.Reset()
_, errRecv := msg.ReceiveProto(this.msn, reqHeader, &message)
if errRecv != nil {
this.Errorf("could not receive elect response from %s: %v", target,
errRecv)
return "", -1, errRecv
}
if message.ElectResponse == nil {
this.Errorf("elect response from %s is empty", target)
return "", -1, errs.ErrCorrupt
}
response := message.GetElectResponse()
change := thispb.ElectionChange{}
change.ElectionRound = response.ElectionRound
change.ElectionWinner = response.ElectionWinner
if err := this.UpdateElection(&change); err != nil {
this.Errorf("could not update to new election round: %v", err)
return "", -1, err
}
newRound := response.GetElectionRound()
newLeader := response.GetElectionWinner()
return newLeader, newRound, nil
}
// ElectRPC implements the Election.Elect rpc.
func (this *Election) ElectRPC(reqHeader *msgpb.Header,
request *thispb.ElectRequest) (status error) {
if !this.InCommittee() {
return errs.ErrInvalid
}
round := request.GetElectionRound()
current := this.CurrentRound()
if round != current+1 {
this.Errorf("could not begin election round %d because current round "+
"is only at %d", round, current)
return errs.ErrStale
}
uid := this.PaxosUIDFromElectionRound(round)
paxos, errGet := this.GetPaxosInstance(uid)
if errGet != nil {
this.Errorf("could not find paxos instance for uid %s: %v", uid, errGet)
return errGet
}
this.Infof("starting new election for round %d using paxos instance %s",
round, uid)
clientID := reqHeader.GetMessengerId()
proposedValue := []byte(clientID)
chosenValue, errPropose := paxos.Propose(proposedValue,
msg.RequestTimeout(reqHeader))
if errPropose != nil {
this.Errorf("could not propose %s as the leader for election round %d: %v",
proposedValue, round, errPropose)
return errPropose
}
winner := string(chosenValue)
// Send the election result.
response := thispb.ElectResponse{}
response.ElectionRound = proto.Int64(round)
response.ElectionWinner = proto.String(winner)
message := thispb.ElectionMessage{}
message.ElectResponse = &response
if err := msg.SendResponseProto(this.msn, reqHeader, &message); err != nil {
this.Errorf("could not send election response to %s: %v", clientID, err)
return err
}
return nil
}
