fix a bug that could cause "Helium.dispatch" to panic (#552)

Author: DuodenumL

discovery/helium/helium.go

@@ -15,6 +15,7 @@ import (
 // Helium .
 type Helium struct {
 	sync.Once
+	lock   *sync.RWMutex
 	config types.GRPCConfig
 	stor   store.Store
 	subs   sync.Map
@@ -25,6 +26,7 @@ func New(config types.GRPCConfig, stor store.Store) *Helium {
 	h := &Helium{}
 	h.config = config
 	h.stor = stor
+	h.lock = &sync.RWMutex{}
 	h.Do(func() {
 		h.start(context.TODO()) // TODO rewrite ctx here, because this will run only once!
 	})
@@ -33,13 +35,17 @@ func New(config types.GRPCConfig, stor store.Store) *Helium {
 
 // Subscribe .
 func (h *Helium) Subscribe(ch chan<- types.ServiceStatus) uuid.UUID {
+	h.lock.Lock()
+	defer h.lock.Unlock()
 	id := uuid.New()
 	_, _ = h.subs.LoadOrStore(id, ch)
 	return id
 }
 
 // Unsubscribe .
 func (h *Helium) Unsubscribe(id uuid.UUID) {
+	h.lock.Lock()
+	defer h.lock.Unlock()
 	h.subs.Delete(id)
 }
 
@@ -77,7 +83,14 @@ func (h *Helium) start(ctx context.Context) {
 }
 
 func (h *Helium) dispatch(status types.ServiceStatus) {
+	h.lock.RLock()
+	defer h.lock.RUnlock()
 	h.subs.Range(func(k, v interface{}) bool {
+		defer func() {
+			if err := recover(); err != nil {
+				log.Errorf(context.TODO(), "[dispatch] dispatch %s failed, err: %v", k, err)
+			}
+		}()
 		c, ok := v.(chan<- types.ServiceStatus)
 		if !ok {
 			log.Error("[WatchServiceStatus] failed to cast channel from map")

discovery/helium/helium_test.go

@@ -47,3 +47,33 @@ func TestHelium(t *testing.T) {
 	close(chAddr)
 	close(chStatus)
 }
+
+func TestPanic(t *testing.T) {
+	chAddr := make(chan []string)
+
+	store := &storemocks.Store{}
+	store.On("ServiceStatusStream", mock.Anything).Return(chAddr, nil)
+
+	grpcConfig := types.GRPCConfig{
+		ServiceDiscoveryPushInterval: time.Duration(1) * time.Second,
+	}
+	service := New(grpcConfig, store)
+
+	for i := 0; i < 1000; i++ {
+		go func() {
+			chStatus := make(chan types.ServiceStatus)
+			uuid := service.Subscribe(chStatus)
+			time.Sleep(time.Second)
+			service.Unsubscribe(uuid)
+			close(chStatus)
+		}()
+	}
+
+	go func() {
+		for i := 0; i < 1000; i++ {
+			chAddr <- []string{"hhh", "hhh2"}
+		}
+	}()
+
+	time.Sleep(5 * time.Second)
+}