cloudcommon: elect: notifyOne on subscribe

pkg/cloudcommon/elect/elect.go

@@ -72,6 +72,7 @@ type Elect struct {
 	config *EtcdConfig
 
 	mutex       *sync.Mutex
+	latestEv    electEvent
 	subscribers []chan electEvent
 }
 
@@ -104,10 +105,12 @@ func NewElect(config *EtcdConfig, key string) (*Elect, error) {
 		return nil, errors.Wrap(err, "new etcd client")
 	}
 	elect := &Elect{
-		cli:   cli,
-		path:  config.LockPrefix + "/" + key,
-		ttl:   config.LockTTL,
-		mutex: &sync.Mutex{},
+		cli:  cli,
+		path: config.LockPrefix + "/" + key,
+		ttl:  config.LockTTL,
+
+		mutex:    &sync.Mutex{},
+		latestEv: electEventInit,
 	}
 	return elect, nil
 }
@@ -173,31 +176,43 @@ func (elect *Elect) do(ctx context.Context) (*ticket, error) {
 	return r, err
 }
 
-func (elect *Elect) subscribe(ch chan electEvent) {
+func (elect *Elect) subscribe(ctx context.Context, ch chan electEvent) {
 	elect.mutex.Lock()
 	defer elect.mutex.Unlock()
 	elect.subscribers = append(elect.subscribers, ch)
+	if ev := elect.latestEv; ev != electEventInit {
+		elect.notifyOne(ctx, ev, ch)
+	}
+}
+
+func (elect *Elect) notifyOne(ctx context.Context, ev electEvent, ch chan electEvent) {
+	sent := false
+	select {
+	case ch <- ev:
+		sent = true
+	case <-ctx.Done():
+	default:
+	}
+	if !sent {
+		log.Errorf("elect event '%s' missed by %#v", ev, ch)
+	}
 }
 
 func (elect *Elect) notify(ctx context.Context, ev electEvent) {
 	elect.mutex.Lock()
 	defer elect.mutex.Unlock()
 
+	elect.latestEv = ev
 	for _, ch := range elect.subscribers {
-		select {
-		case ch <- ev:
-		case <-ctx.Done():
-			return
-		default:
-		}
+		elect.notifyOne(ctx, ev, ch)
 	}
 }
 
 func (elect *Elect) SubscribeWithAction(ctx context.Context, onWin, onLost func()) {
 	go func() {
 		ch := make(chan electEvent, 3)
 		var ev electEvent
-		elect.subscribe(ch)
+		elect.subscribe(ctx, ch)
 		for {
 			select {
 			case ev = <-ch:
@@ -229,6 +244,7 @@ type electEvent int
 const (
 	electEventWin electEvent = iota
 	electEventLost
+	electEventInit
 )
 
 func (ev electEvent) String() string {
@@ -237,6 +253,8 @@ func (ev electEvent) String() string {
 		return "win"
 	case electEventLost:
 		return "lost"
+	case electEventInit:
+		return "init"
 	default:
 		return "unexpected"
 	}