// Top-level function of the processing goroutine.
func process() {
connections = make(map[uint16][]*connect.BaseConn)
// On startup, make an outgoing connection attempt to all other
// core nodes, before continuing.
for _, node := range config.CoreNodes() {
if node == config.Id() {
continue
}
conn, err := connect.Dial(
connect.CONSENSUS_PROTOCOL, node)
if err != nil {
// Can't reach the other node.
continue
}
log.Print("core/consensus: made outgoing connection to ", node)
connections[node] = append(connections[node], conn)
go handleConn(node, conn)
}
// Retry connections once per config.CHANGE_TIMEOUT_PERIOD.
// Largely arbitrary.
reconnectTicker := time.Tick(config.CHANGE_TIMEOUT_PERIOD)
for {
select {
// Connection retry tick.
// We should try to make an outgoing connection to any node
// that we do not have at least one connection to.
// We need to make these asynchronously, because connections
// are slow.
case <-reconnectTicker:
for _, node := range config.CoreNodes() {
if node == config.Id() {
continue
}
if len(connections[node]) > 0 {
continue
}
go outgoingConn(node)
}
// New change request, for us to propose as leader.
case req := <-newChangeCh:
store.StartTransaction()
if !amLeader && receivedPromises != nil {
waitingRequests = append(waitingRequests, req)
} else if !amLeader {
waitingRequests = append(waitingRequests, req)
// Start attempting to be leader.
m := make(map[uint16]*coproto.Promise)
receivedPromises = m
proposal, _ := store.Proposal()
proposal++
store.SetProposal(proposal, config.Id())
firstUn := store.InstructionFirstUnapplied()
// Send prepare messages to all other nodes.
var prepare coproto.Prepare
prepare.Proposal = new(uint64)
prepare.FirstUnapplied = new(uint64)
*prepare.Proposal = proposal
*prepare.FirstUnapplied = firstUn
for _, node := range config.CoreNodes() {
if node == config.Id() {
continue
}
if len(connections[node]) != 0 {
c := connections[node][0]
c.SendProto(2, &prepare)
}
}
// Behave as if we got a promise message
// from ourselves.
var promise coproto.Promise
promise.Proposal = prepare.Proposal
promise.PrevProposal = promise.Proposal
promise.Leader = new(uint32)
*promise.Leader = uint32(config.Id())
promise.PrevLeader = promise.Leader
addPromise(config.Id(), &promise)
} else {
newSlot := nextProposalSlot
nextProposalSlot++
addProposalTimeout(newSlot, req)
proposal, leader := store.Proposal()
inst := makeInst(newSlot, proposal, leader,
req)
sendProposal(inst)
}
store.EndTransaction()
// Leadership attempt timed out.
case timedOutProposal := <-leaderTimeoutCh:
store.StartTransaction()
proposal, leader := store.Proposal()
// If the proposal has changed since that
// leadership attempt, ignore it.
if leader != config.Id() {
return
}
if proposal != timedOutProposal {
return
}
// If we successfully became leader, ignore it.
if amLeader {
return
}
// Otherwise, stop our attempt to become leader.
stopBeingLeader()
store.EndTransaction()
// Proposal timed out.
case timeout := <-proposalTimeoutCh:
store.StartTransaction()
// If this timeout was not canceled, a proposal failed.
// We stop being leader.
if proposalTimeouts[timeout.slot] == timeout {
stopBeingLeader()
}
store.EndTransaction()
// New received connection.
case receivedConn := <-receivedConnCh:
node := receivedConn.node
conn := receivedConn.conn
connections[node] = append(connections[node], conn)
// Received message.
case recvMsg := <-receivedMsgCh:
node := recvMsg.node
conn := recvMsg.conn
msg := recvMsg.msg
switch *msg.MsgType {
case 2:
processPrepare(node, conn, msg.Content)
case 3:
processPromise(node, conn, msg.Content)
case 4:
processAccept(node, conn, msg.Content)
case 5:
processAccepted(node, conn, msg.Content)
case 6:
processNack(node, conn, msg.Content)
default:
// Unknown message.
conn.Close()
}
// Terminate received connection.
case terminatedConn := <-terminatedConnCh:
node := terminatedConn.node
conn := terminatedConn.conn
for i, other := range connections[node] {
if other != conn {
continue
}
conns := connections[node]
conns = append(conns[:i], conns[i+1:]...)
connections[node] = conns
break
}
}
}
}
// Must be called from the processing goroutine.
func processPrepare(node uint16, conn *connect.BaseConn, content []byte) {
var msg coproto.Prepare
if err := proto.Unmarshal(content, &msg); err != nil {
conn.Close()
return
}
store.StartTransaction()
defer store.EndTransaction()
newProposal, newLeader := *msg.Proposal, node
proposal, leader := store.Proposal()
if store.CompareProposals(newProposal, newLeader, proposal, leader) {
log.Print("core/consensus: sending promise to ", newLeader)
// Create a promise message to send back.
var promise coproto.Promise
promise.Proposal = new(uint64)
promise.Leader = new(uint32)
promise.PrevProposal = new(uint64)
promise.PrevLeader = new(uint32)
*promise.Proposal = newProposal
*promise.Leader = uint32(newLeader)
*promise.PrevProposal = proposal
*promise.PrevLeader = uint32(leader)
// Add all the instructions we've previously accepted or chosen.
slots := store.InstructionSlots()
theirFirstUnapplied := *msg.FirstUnapplied
ourStart := store.InstructionStart()
relativeSlot := int(theirFirstUnapplied - ourStart)
if relativeSlot < 0 {
relativeSlot = 0
}
var accepted []*coproto.Instruction
for ; relativeSlot < len(slots); relativeSlot++ {
slot := slots[relativeSlot]
slotNum := ourStart + uint64(relativeSlot)
for i, _ := range slot {
if slot[i].IsChosen() {
appendInst(&accepted, slotNum, slot[i])
break
}
weAccepted := false
for _, node := range slot[i].Accepted() {
if node == config.Id() {
weAccepted = true
break
}
}
if weAccepted {
appendInst(&accepted, slotNum, slot[i])
break
}
}
}
// Send promise message.
conn.SendProto(3, &promise)
// Accept the other node as our new leader.
store.SetProposal(newProposal, newLeader)
} else {
var nack coproto.Nack
nack.Proposal = new(uint64)
nack.Leader = new(uint32)
*nack.Proposal = proposal
*nack.Leader = uint32(leader)
conn.SendProto(6, &nack)
}
}