[Dubbo add comments for RegistryDirectory]Add comments

dubbo-registry/dubbo-registry-api/src/main/java/org/apache/dubbo/registry/integration/RegistryDirectory.java

@@ -216,9 +216,7 @@ private void refreshOverrideAndInvoker(List<URL> urls) {
     private void refreshInvoker(List<URL> invokerUrls) {
         Assert.notNull(invokerUrls, "invokerUrls should not be null");
 
-        if (invokerUrls.size() == 1 && invokerUrls.get(0) != null && Constants.EMPTY_PROTOCOL.equals(invokerUrls
-                .get(0)
-                .getProtocol())) {
+        if (invokerUrls.size() == 1 && Constants.EMPTY_PROTOCOL.equals(invokerUrls.get(0).getProtocol())) {
             this.forbidden = true; // Forbid to access
             this.invokers = Collections.emptyList();
             routerChain.setInvokers(this.invokers);
@@ -240,8 +238,14 @@ private void refreshInvoker(List<URL> invokerUrls) {
             }
             Map<String, Invoker<T>> newUrlInvokerMap = toInvokers(invokerUrls);// Translate url list to Invoker map
 
-            // state change
-            // If the calculation is wrong, it is not processed.
+            /**
+             * If the calculation is wrong, it is not processed.
+             *
+             * 1. The protocol configured by the client is inconsistent with the protocol of the server.
+             *    eg: consumer protocol = dubbo, provider only has other protocol services(rest).
+             * 2. The registration center is not robust and pushes illegal specification data.
+             *
+             */
             if (newUrlInvokerMap == null || newUrlInvokerMap.size() == 0) {
                 logger.error(new IllegalStateException("urls to invokers error .invokerUrls.size :" + invokerUrls.size() + ", invoker.size :0. urls :" + invokerUrls
                         .toString()));

dubbo-remoting/dubbo-remoting-api/src/main/java/org/apache/dubbo/remoting/transport/AbstractClient.java

@@ -152,6 +152,8 @@ private synchronized void initConnectStatusCheckCommand() {
                 @Override
                 public void run() {
                     try {
+                        if (cancelFutureIfOffline()) return;
+
                         if (!isConnected()) {
                             connect();
                         } else {
@@ -172,7 +174,29 @@ public void run() {
                         }
                     }
                 }
+
+                private boolean cancelFutureIfOffline() {
+                    /**
+                     * If the provider service is detected offline,
+                     * the client should not attempt to connect again.
+                     *
+                     * issue: https://github.com/apache/incubator-dubbo/issues/3158
+                     */
+                    if(isClosed()) {
+                        ScheduledFuture<?> future = reconnectExecutorFuture;
+                        if(future != null && !future.isCancelled()){
+                            /**
+                             *  Client has been destroyed and
+                             *  scheduled task should be cancelled.
+                             */
+                            future.cancel(true);
+                        }
+                        return true;
+                    }
+                    return false;
+                }
             };
+
             reconnectExecutorFuture = reconnectExecutorService.scheduleWithFixedDelay(connectStatusCheckCommand, reconnect, reconnect, TimeUnit.MILLISECONDS);
         }
     }
@@ -344,14 +368,14 @@ public void reconnect() throws RemotingException {
     @Override
     public void close() {
         try {
-            if (executor != null) {
-                ExecutorUtil.shutdownNow(executor, 100);
-            }
+            super.close();
         } catch (Throwable e) {
             logger.warn(e.getMessage(), e);
         }
         try {
-            super.close();
+            if (executor != null) {
+                ExecutorUtil.shutdownNow(executor, 100);
+            }
         } catch (Throwable e) {
             logger.warn(e.getMessage(), e);
         }