raft: block ReadState until state updates

raft2/node.go

@@ -9,6 +9,10 @@ type stateResp struct {
 	msgs        []Message
 }
 
+func (sr stateResp) containsUpdates(prev stateResp) bool {
+	return !prev.state.Equal(sr.state) || len(sr.ents) > 0 || len(sr.cents) > 0 || len(sr.msgs) > 0
+}
+
 type Node struct {
 	ctx    context.Context
 	propc  chan []byte
@@ -36,7 +40,9 @@ func Start(ctx context.Context, name string, election, heartbeat int) *Node {
 
 func (n *Node) run(r *raft) {
 	propc := n.propc
+	statec := n.statec
 
+	var prev stateResp
 	for {
 		if r.hasLeader() {
 			propc = n.propc
@@ -54,6 +60,12 @@ func (n *Node) run(r *raft) {
 			r.msgs,
 		}
 
+		if sr.containsUpdates(prev) {
+			statec = n.statec
+		} else {
+			statec = nil
+		}
+
 		select {
 		case p := <-propc:
 			r.propose(p)
@@ -61,7 +73,7 @@ func (n *Node) run(r *raft) {
 			r.Step(m) // raft never returns an error
 		case <-n.tickc:
 			// r.tick()
-		case n.statec <- sr:
+		case statec <- sr:
 			r.raftLog.resetNextEnts()
 			r.raftLog.resetUnstable()
 			r.msgs = nil