fix coredump

remoting/zookeeper/client.go

@@ -51,7 +51,7 @@ var (
 type ZookeeperClient struct {
 	name          string
 	ZkAddrs       []string
-	sync.Mutex    // for conn
+	sync.RWMutex    // for conn
 	Conn          *zk.Conn
 	Timeout       time.Duration
 	exit          chan struct{}

remoting/zookeeper/listener.go

@@ -239,8 +239,13 @@ func (l *ZkEventListener) listenDirEvent(zkPath string, listener remoting.DataLi
 			l.pathMapLock.Lock()
 			l.pathMap[dubboPath] = struct{}{}
 			l.pathMapLock.Unlock()
-
+			//When Zk disconnected, the Conn will be set to nil, so here need check the value of Conn
+			l.client.RLock()
+			if l.client.Conn == nil{
+				break
+			}
 			content, _, err := l.client.Conn.Get(dubboPath)
+			l.client.RUnlock()
 			if err != nil {
 				logger.Errorf("Get new node path {%v} 's content error,message is  {%v}", dubboPath, perrors.WithStack(err))
 			}