Support multiple shared links

dubbo-rpc/dubbo-rpc-dubbo/src/main/java/org/apache/dubbo/rpc/protocol/dubbo/DubboProtocol.java

@@ -69,14 +69,24 @@ public class DubboProtocol extends AbstractProtocol {
     public static final int DEFAULT_PORT = 20880;
     private static final String IS_CALLBACK_SERVICE_INVOKE = "_isCallBackServiceInvoke";
     private static DubboProtocol INSTANCE;
-    private final Map<String, ExchangeServer> serverMap = new ConcurrentHashMap<String, ExchangeServer>(); // <host:port,Exchanger>
-    private final Map<String, List<ReferenceCountExchangeClient>> referenceClientMap = new ConcurrentHashMap<>(); // <host:port,Exchanger>
-    private final ConcurrentMap<String, LazyConnectExchangeClient> ghostClientMap = new ConcurrentHashMap<String, LazyConnectExchangeClient>();
-    private final ConcurrentMap<String, Object> locks = new ConcurrentHashMap<String, Object>();
-    private final Set<String> optimizers = new ConcurrentHashSet<String>();
-    //consumer side export a stub service for dispatching event
-    //servicekey-stubmethods
-    private final ConcurrentMap<String, String> stubServiceMethodsMap = new ConcurrentHashMap<String, String>();
+
+    /**
+     * <host:port,Exchanger>
+     */
+    private final Map<String, ExchangeServer> serverMap = new ConcurrentHashMap<>();
+    /**
+     * <host:port,Exchanger>
+     */
+    private final Map<String, List<ReferenceCountExchangeClient>> referenceClientMap = new ConcurrentHashMap<>();
+    private final ConcurrentMap<String, LazyConnectExchangeClient> ghostClientMap = new ConcurrentHashMap<>();
+    private final ConcurrentMap<String, Object> locks = new ConcurrentHashMap<>();
+    private final Set<String> optimizers = new ConcurrentHashSet<>();
+    /**
+     * consumer side export a stub service for dispatching event
+     * servicekey-stubmethods
+     */
+    private final ConcurrentMap<String, String> stubServiceMethodsMap = new ConcurrentHashMap<>();
+
     private ExchangeHandler requestHandler = new ExchangeHandlerAdapter() {
 
         @Override