Fix bug: state not updated when GRPC auto reconnect to the same server (#3181)

apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/remote/GRPCChannel.java

@@ -19,6 +19,7 @@
 package org.apache.skywalking.apm.agent.core.remote;
 
 import io.grpc.Channel;
+import io.grpc.ConnectivityState;
 import io.grpc.ManagedChannel;
 import io.grpc.ManagedChannelBuilder;
 import io.grpc.netty.NettyChannelBuilder;
@@ -73,6 +74,10 @@ public class GRPCChannel {
         return originChannel.isShutdown();
     }
 
+    public boolean isConnected() {
+        return originChannel.getState(false) == ConnectivityState.READY;
+    }
+
     public static class Builder {
         private final String host;
         private final int port;

apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/remote/GRPCChannelManager.java

@@ -105,9 +105,15 @@ public class GRPCChannelManager implements BootService, Runnable {
                             .build();
 
                         notify(GRPCChannelStatus.CONNECTED);
+                        reconnect = false;
+                    } else if (managedChannel.isConnected()) {
+                        // Reconnect to the same server is automatically done by GRPC,
+                        // therefore we are responsible to check the connectivity and
+                        // set the state and notify listeners
+                        notify(GRPCChannelStatus.CONNECTED);
+                        reconnect = false;
                     }
 
-                    reconnect = false;
                     return;
                 } catch (Throwable t) {
                     logger.error(t, "Create channel to {} fail.", server);