// Sets this instruction value as accepted by the given node ID.
// Safe to call more than once with the same node ID.
// If the given current proposal number and leader node ID are
// higher than our latest proposal number and leader node ID that
// this instruction was accepted in, we update our latest proposal number and
// leader node ID that this instruction was accepted in.
//
// Will automatically cause the instruction value to become chosen,
// with all other instruction values in the same slot cleared,
// once a majority of nodes have accepted it,
// and automatically cause it to be applied to state once all
// previous instruction slots have a chosen value.
func (i *InstructionValue) Accept(id uint16, proposal uint64, leader uint16) {
if CompareProposals(proposal, id, i.latestProposal, i.latestLeader) {
i.latestProposal = proposal
i.latestLeader = leader
}
// If this value is already chosen, acceptance changes nothing.
if i.chosen {
return
}
// If this node ID already accepted this instruction value,
// don't add it twice.
for _, node := range i.acceptedBy {
if node == id {
return
}
}
// Add this node ID to the accepting list.
i.acceptedBy = append(i.acceptedBy, id)
// If a majority of nodes have accepted this instruction value,
// make it chosen.
if len(i.acceptedBy) > len(config.CoreNodes())/2 {
i.Choose()
}
}
// May only be called by the processing goroutine, in a transaction.
func sendProposal(inst *coproto.Instruction) {
// We must be leader.
proposal, leader := store.Proposal()
if leader != config.Id() || !amLeader {
panic("tried to send accept messages while not leader")
}
// Send accept messages to all other core nodes.
var accept coproto.Accept
accept.Proposal = new(uint64)
*accept.Proposal = proposal
accept.Instruction = inst
for _, node := range config.CoreNodes() {
if node == config.Id() {
continue
}
if len(connections[node]) != 0 {
c := connections[node][0]
c.SendProto(4, &accept)
}
}
// Behave as if we received our own accept message.
addAccept(config.Id(), &accept)
}
// Must be called from the processing goroutine, inside a transaction.
// Handle an accept message that we've decided to respond to.
// Called directly when we send accepted messages to other nodes.
func addAccept(node uint16, msg *coproto.Accept) {
// Send an accepted message to all other core nodes reachable.
var accepted coproto.Accepted
accepted.Proposal = msg.Proposal
accepted.Leader = new(uint32)
*accepted.Leader = uint32(node)
accepted.Instruction = msg.Instruction
// We must do this before sending accepted messages.
// We behave as if we received one from ourselves.
if !addAccepted(config.Id(), &accepted) {
// Required too large an instruction slots slice.
// We have NOT accepted this accept message,
// and must NOT send accepted messages.
return
}
for _, node := range config.CoreNodes() {
if node == config.Id() {
continue
}
if len(connections[node]) > 0 {
connections[node][0].SendProto(5, &accepted)
}
}
}
func process() {
for {
select {
// Try to make any needed outgoing connections.
case <-tryOutgoingCh:
store.StartTransaction()
connectionsLock.Lock()
coreNodes := config.CoreNodes()
if !store.Degraded() {
if config.IsCore() {
for _, node := range coreNodes {
if node == config.Id() {
continue
}
if connections[node] == nil {
go tryOutgoing(node)
}
}
} else {
// Settle for less than 2 core nodes,
// if there *aren't* 2 core nodes.
targetConns := 2
if targetConns > len(coreNodes) {
targetConns = len(coreNodes)
}
newOutgoing := targetConns -
len(connections)
used := -1
for newOutgoing > 0 {
r := processRand.Intn(
len(coreNodes))
// Don't do the same node
// twice.
if r == used {
continue
}
node := coreNodes[r]
if connections[node] == nil {
used = r
go tryOutgoing(node)
newOutgoing--
}
}
}
} else {
if len(connections) == 0 {
r := processRand.Intn(len(coreNodes))
node := coreNodes[r]
if connections[node] == nil {
go tryOutgoing(node)
}
}
}
connectionsLock.Unlock()
store.EndTransaction()
// After a random time, check again.
randDur := time.Duration(processRand.Intn(19)+1) * time.Second
tryOutgoingCh = time.NewTimer(randDur).C
// New received connection.
case conn := <-receivedConnCh:
conn.offerTimers = make(map[uint64]*time.Timer)
store.StartTransaction()
connectionsLock.Lock()
// If we are degraded, reject the connection,
// unless we have no other connection,
// and it is outbound.
if store.Degraded() &&
!(len(connections) == 0 && conn.outgoing) {
conn.lock.Lock()
conn.Close()
conn.lock.Unlock()
connectionsLock.Unlock()
store.EndTransaction()
break
}
// If we have an existing connection to this node,
// close it.
if connections[conn.node] != nil {
other := connections[conn.node]
other.lock.Lock()
other.Close()
if other.firstUnappliedTimer != nil {
other.firstUnappliedTimer.Stop()
}
other.lock.Unlock()
}
// Add to our connections.
connections[conn.node] = conn
// Send initial position and leader messages.
posMsg := new(fproto.Position)
posMsg.FirstUnapplied = new(uint64)
posMsg.Degraded = new(bool)
*posMsg.FirstUnapplied =
store.InstructionFirstUnapplied()
*posMsg.Degraded = store.Degraded()
conn.conn.SendProto(2, posMsg)
proposal, leader := store.Proposal()
leaderMsg := new(fproto.Leader)
leaderMsg.Proposal = new(uint64)
leaderMsg.Leader = new(uint32)
*leaderMsg.Proposal = proposal
*leaderMsg.Leader = uint32(leader)
conn.conn.SendProto(11, leaderMsg)
connectionsLock.Unlock()
store.EndTransaction()
// Start timer for sending first unapplied
// instruction updates.
if config.IsCore() && conn.node <= 0x2000 {
conn.lock.Lock()
conn.firstUnappliedTimer = time.AfterFunc(
firstUnappliedTimerDuration,
func() { conn.firstUnappliedTimeout() })
conn.lock.Unlock()
}
// Start handling received messages from the connection.
go handleConn(conn)
// Terminated connection.
case conn := <-terminatedConnCh:
connectionsLock.Lock()
if connections[conn.node] == conn {
delete(connections, conn.node)
conn.lock.Lock()
conn.closed = true
if conn.firstUnappliedTimer != nil {
conn.firstUnappliedTimer.Stop()
}
conn.lock.Unlock()
}
connectionsLock.Unlock()
}
}
}
// Handle a received change forward. Decides which node is responsible for it.
// Must only be called from the processing goroutine.
func processForward(forward *chproto.ChangeForward) {
// If we are already trying to forward a change forward message with
// the same requesting node and request ID, discard this message.
if _, exists := getForwardTimeout(uint16(*forward.Request.RequestNode),
*forward.Request.RequestId); exists {
return
}
// Everything else in this function runs in a transaction.
// We are read-only.
store.StartTransaction()
defer store.EndTransaction()
// If this is a core node and this node stopped being leader less than
// a Change Timeout Period ago, always add us to the ignore list.
if config.IsCore() && !isIgnored(forward, config.Id()) {
diff := time.Now().Sub(store.StoppedLeading())
if diff < config.CHANGE_TIMEOUT_PERIOD {
forward.Ignores = append(forward.Ignores,
uint32(config.Id()))
}
}
// If all core node IDs are in the forward's ignore list, discard it.
if len(forward.Ignores) == len(config.CoreNodes()) {
log.Print("shared/chrequest: dropped msg due to full ignores")
return
}
// Otherwise, choose a potential leader node.
// This is O(n^2) in the number of core nodes,
// but we don't expect to have many.
chosenNode := uint16(0)
_, leader := store.Proposal()
if leader != 0 && !isIgnored(forward, leader) {
chosenNode = leader
} else {
for _, node := range config.CoreNodes() {
if !isIgnored(forward, node) {
chosenNode = node
break
}
}
}
if chosenNode == 0 {
// Shouldn't happen.
log.Print("shared/chrequest: bug, " +
"couldn't find candidate leader node")
return
}
// If we are the selected leader, construct an external change request,
// and send it on our change request channel.
if chosenNode == config.Id() {
intRequest := forward.Request
chrequest := new(store.ChangeRequest)
chrequest.RequestEntity = *intRequest.RequestEntity
chrequest.RequestNode = uint16(*intRequest.RequestNode)
chrequest.RequestId = *intRequest.RequestId
chrequest.Changeset = make([]store.Change,
len(intRequest.Changeset))
for i, ch := range intRequest.Changeset {
chrequest.Changeset[i].TargetEntity = *ch.TargetEntity
chrequest.Changeset[i].Key = *ch.Key
chrequest.Changeset[i].Value = *ch.Value
}
for _, cb := range changeCallbacks {
cb(chrequest)
}
return
}
// Otherwise, we send it on to the selected leader,
// add the selected leader to the ignore list,
// and set a timeout to retry.
sendForward(chosenNode, forward)
forward.Ignores = append(forward.Ignores, uint32(chosenNode))
addForwardTimeout(forward)
}
// Sets this instruction value as chosen, clearing all others in the same slot.
// Causes it to be automatically applied to state once all previous instruction
// slots have a chosen value.
func (i *InstructionValue) Choose() {
log.Print("shared/store: choosing instruction in slot ", i.slot)
relativeSlot := i.slot - start
// Drop all other instruction values in the same slot.
if len(slots[relativeSlot]) > 1 {
slots[relativeSlot] = []*InstructionValue{i}
}
// Set the value as chosen.
i.chosen = true
i.chosenTime = time.Now()
i.acceptedBy = nil
// Call instruction chosen callbacks.
for _, cb := range chosenCallbacks {
cb(i.slot)
}
// Apply instructions as far as possible.
tryApply()
// Discard no longer needed instructions, from the start.
newStart := start
for {
relative := newStart - start
// If we've not applied the instruction yet,
// we still need it.
if firstUnapplied == newStart {
break
}
// If the instruction wasn't chosen long enough ago,
// we can't discard it.
minDelay := time.Duration(4) * config.CHANGE_TIMEOUT_PERIOD
timeChosen := slots[relative][0].TimeChosen()
if time.Now().Sub(timeChosen) < minDelay {
break
}
// If this is a core node and the majority of core nodes aren't
// past this point, we have to keep it.
if config.IsCore() {
past := 1 // We are past it.
coreNodes := config.CoreNodes()
for _, node := range coreNodes {
if node == config.Id() {
continue
}
if NodeFirstUnapplied(node) > newStart {
past++
}
}
if past <= len(coreNodes)/2 {
break
}
}
newStart++
}
// If we can discard, do it by reslicing the slots.
// This doesn't result in an immediate free,
// but will when we next expand the slots.
// This avoids extra performance costs for reallocating them now.
if newStart != start {
log.Print("Discarding instructions between ", newStart-1,
" and ", start)
slots = slots[newStart-start:]
start = newStart
}
}
// Must be called from the processing goroutine, inside a transaction.
func addPromise(node uint16, msg *coproto.Promise) {
receivedPromises[node] = msg
// If we have promises from a majority of core nodes,
// become leader.
if len(receivedPromises) > len(config.CoreNodes())/2 {
log.Print("core/consensus: became leader")
stopLeaderTimeout()
amLeader = true
proposal, leader := store.Proposal()
// Find a slot number above all those in promise messages,
// and above our first unapplied.
firstUnapplied := store.InstructionFirstUnapplied()
limit := firstUnapplied
for _, msg := range receivedPromises {
for _, accepted := range msg.Accepted {
if *accepted.Slot >= limit {
limit = *accepted.Slot + 1
}
}
}
// Start our next slot after the limit.
nextProposalSlot = limit
// For all slots between this and our first unapplied,
// submit a previously accepted instruction unless we
// know an instruction was already chosen.
// Fills these slots with proposals.
// This is O(n^2) in the number of instructions between our
// first unapplied and limit.
// TODO: Improve worst-case complexity.
start := store.InstructionStart()
slots := store.InstructionSlots()
for i := firstUnapplied; i < limit; i++ {
// If we already have a chosen instruction, skip.
rel := int(i - start)
if len(slots[rel]) == 1 && slots[rel][0].IsChosen() {
continue
}
// Find the previously accepted instruction
// accepted with the highest proposal number.
var bestInst *coproto.Instruction
var bp uint64 // Best proposal
var bl uint16 // Best leader
for _, msg := range receivedPromises {
for _, accepted := range msg.Accepted {
if *accepted.Slot != i {
continue
}
if bestInst == nil {
bestInst = accepted
bp = *accepted.Proposal
bl = uint16(*accepted.Leader)
continue
}
// TODO: This indent is just absurd.
p := *accepted.Proposal
l := uint16(*accepted.Leader)
if store.CompareProposals(p, l,
bp, bl) {
bestInst = accepted
bp = *accepted.Proposal
bl = uint16(*accepted.Leader)
}
}
}
// If we didn't find an instruction, make an empty one.
if bestInst == nil {
empty := new(coproto.ChangeRequest)
empty.RequestEntity = new(uint64)
empty.RequestNode = new(uint32)
*empty.RequestEntity = uint64(config.Id())
*empty.RequestNode = uint32(config.Id())
bestInst := new(coproto.Instruction)
bestInst.Slot = new(uint64)
*bestInst.Slot = i
bestInst.Request = empty
}
// Add proposal timeout.
req := makeExtChangeRequest(bestInst.Request)
addProposalTimeout(i, req)
// Send proposal.
bestInst.Proposal = new(uint64)
bestInst.Leader = new(uint32)
*bestInst.Proposal = proposal
*bestInst.Leader = uint32(leader)
sendProposal(bestInst)
}
// Discard received promise messages.
receivedPromises = nil
// Make an instruction proposal for each waiting change.
for _, req := range waitingRequests {
slot := nextProposalSlot
nextProposalSlot++
addProposalTimeout(slot, req)
inst := makeInst(slot, proposal, leader, req)
sendProposal(inst)
}
// Clear waiting changes.
waitingRequests = nil
}
}
// 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
}
}
}
}