// 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)
}
