trigger init router for first call

cluster/router/chain/chain.go

@@ -65,6 +65,8 @@ type RouterChain struct {
 	notify chan struct{}
 	// Address cache
 	cache atomic.Value
+	// init
+	init sync.Once
 }
 
 // Route Loop routers in RouterChain and call Route method to determine the target invokers list.
@@ -111,6 +113,11 @@ func (c *RouterChain) SetInvokers(invokers []protocol.Invoker) {
 	c.invokers = invokers
 	c.mutex.Unlock()
 
+	// it should trigger init router for first call
+	c.init.Do(func() {
+		c.notify <- struct{}{}
+	})
+
 	c.count++
 	now := time.Now()
 	if c.count >= countThreshold && now.Sub(c.last) >= timeThreshold {