Eliminate doFallbackForAuthority since it became a simple call to man…

…ageControlPlaneClient

xds/src/main/java/io/grpc/xds/client/XdsClientImpl.java

@@ -311,11 +311,13 @@ private <T extends ResourceUpdate> CpcWithFallbackState manageControlPlaneClient
       }
 
       ControlPlaneClient activeCpClient = getActiveCpc(subscriber.authority);
-      if (cpcToUse != activeCpClient && activeCpClient != null) {
-        didFallback = fallBackToCpc(cpcToUse, subscriber.authority, activeCpClient);
-      }
+      if (cpcToUse != activeCpClient) {
+        if (activeCpClient != null) {
+          didFallback = fallBackToCpc(cpcToUse, subscriber.authority, activeCpClient);
+        }
 
-      addCpcToAuthority(subscriber.authority, cpcToUse); // makes it active
+        addCpcToAuthority(subscriber.authority, cpcToUse); // makes it active
+      }
       cpcToUse.adjustResourceSubscription(subscriber.type);
     } else {
       logger.log(XdsLogLevel.WARNING,
@@ -658,20 +660,6 @@ private void shutdownLowerPriorityCpcs(ControlPlaneClient activatedCpc) {
     }
   }
 
-  /**
-   * Try to fallback to a lower priority control plane client.
-   *
-   * @return true if a fallback was successful, false otherwise.
-   */
-  private boolean doFallbackForAuthority(ResourceSubscriber<? extends ResourceUpdate> subscriber) {
-    List<ServerInfo> serverInfos = getServerInfos(subscriber.authority);
-    if (serverInfos == null || serverInfos.size() < 2) {
-      return false;
-    }
-
-    return manageControlPlaneClient(subscriber).didFallback;
-  }
-
   private boolean fallBackToCpc(ControlPlaneClient fallbackCpc, String authority,
                                 ControlPlaneClient oldCpc) {
     boolean didFallback = false;
@@ -1015,7 +1003,7 @@ public void handleStreamClosed(Status status, boolean inRetry) {
           }
 
           // try to fallback to lower priority control plane client
-          if (checkForFallback && doFallbackForAuthority(subscriber)) {
+          if (checkForFallback && manageControlPlaneClient(subscriber).didFallback) {
             authoritiesForClosedCpc.remove(subscriber.authority);
             if (authoritiesForClosedCpc.isEmpty()) {
               return; // optimization: no need to continue once all authorities have done fallback