xds: Avoid changing cache when watching children in XdsDepManager

The watchers can be completely regular, so the base class can do the
cache management while the subclasses are only concerned with
subscribing to children.

xds/src/main/java/io/grpc/xds/XdsDependencyManager.java

@@ -333,7 +333,8 @@ final class XdsDependencyManager implements XdsConfig.XdsClusterSubscriptionRegi
             Status.INTERNAL.withDescription("Logical DNS in dependency manager unsupported")));
         break;
       default:
-        throw new IllegalStateException("Unexpected value: " + cdsUpdate.clusterType());
+        child = new EndpointConfig(StatusOr.fromStatus(Status.UNAVAILABLE.withDescription(
+              "Unknown type in cluster " + clusterName + " " + cdsUpdate.clusterType())));
     }
     if (clusters.containsKey(clusterName)) {
       // If a cycle is detected, we'll have detected it while recursing, so now there will be a key
@@ -520,7 +521,7 @@ final class XdsDependencyManager implements XdsConfig.XdsClusterSubscriptionRegi
       }
       // Don't update configuration on error, if we've already received configuration
       if (!hasDataValue()) {
-        setDataAsStatus(Status.UNAVAILABLE.withDescription(
+        this.data = StatusOr.fromStatus(Status.UNAVAILABLE.withDescription(
             String.format("Error retrieving %s: %s: %s",
               toContextString(), error.getCode(), error.getDescription())));
         maybePublishConfig();
@@ -534,11 +535,25 @@ final class XdsDependencyManager implements XdsConfig.XdsClusterSubscriptionRegi
       }
 
       checkArgument(this.resourceName.equals(resourceName), "Resource name does not match");
-      setDataAsStatus(Status.UNAVAILABLE.withDescription(
+      this.data = StatusOr.fromStatus(Status.UNAVAILABLE.withDescription(
           toContextString() + " does not exist" + nodeInfo()));
       maybePublishConfig();
     }
 
+    @Override
+    public void onChanged(T update) {
+      checkNotNull(update, "update");
+      if (cancelled) {
+        return;
+      }
+
+      this.data = StatusOr.fromValue(update);
+      subscribeToChildren(update);
+      maybePublishConfig();
+    }
+
+    protected abstract void subscribeToChildren(T update);
+
     public void close() {
       cancelled = true;
       xdsClient.cancelXdsResourceWatch(type, resourceName, this);
@@ -557,20 +572,6 @@ final class XdsDependencyManager implements XdsConfig.XdsClusterSubscriptionRegi
       return data != null && data.hasValue();
     }
 
-    String resourceName() {
-      return resourceName;
-    }
-
-    protected void setData(T data) {
-      checkNotNull(data, "data");
-      this.data = StatusOr.fromValue(data);
-    }
-
-    protected void setDataAsStatus(Status status) {
-      checkNotNull(status, "status");
-      this.data = StatusOr.fromStatus(status);
-    }
-
     public String toContextString() {
       return toContextStr(type.typeName(), resourceName);
     }
@@ -588,12 +589,7 @@ final class XdsDependencyManager implements XdsConfig.XdsClusterSubscriptionRegi
     }
 
     @Override
-    public void onChanged(XdsListenerResource.LdsUpdate update) {
-      checkNotNull(update, "update");
-      if (cancelled) {
-        return;
-      }
-
+    public void subscribeToChildren(XdsListenerResource.LdsUpdate update) {
       HttpConnectionManager httpConnectionManager = update.httpConnectionManager();
       List<VirtualHost> virtualHosts;
       if (httpConnectionManager == null) {
@@ -610,9 +606,6 @@ final class XdsDependencyManager implements XdsConfig.XdsClusterSubscriptionRegi
       if (rdsName != null) {
         addRdsWatcher(rdsName);
       }
-
-      setData(update);
-      maybePublishConfig();
     }
 
     private String getRdsName(XdsListenerResource.LdsUpdate update) {
@@ -680,14 +673,8 @@ final class XdsDependencyManager implements XdsConfig.XdsClusterSubscriptionRegi
     }
 
     @Override
-    public void onChanged(RdsUpdate update) {
-      checkNotNull(update, "update");
-      if (cancelled) {
-        return;
-      }
-      setData(update);
+    public void subscribeToChildren(RdsUpdate update) {
       updateRoutes(update.virtualHosts);
-      maybePublishConfig();
     }
 
     @Override
@@ -705,31 +692,20 @@ final class XdsDependencyManager implements XdsConfig.XdsClusterSubscriptionRegi
     }
 
     @Override
-    public void onChanged(XdsClusterResource.CdsUpdate update) {
-      checkNotNull(update, "update");
-      if (cancelled) {
-        return;
-      }
+    public void subscribeToChildren(XdsClusterResource.CdsUpdate update) {
       switch (update.clusterType()) {
         case EDS:
-          setData(update);
           addEdsWatcher(getEdsServiceName());
           break;
         case LOGICAL_DNS:
-          setData(update);
           // no eds needed
           break;
         case AGGREGATE:
-          setData(update);
           update.prioritizedClusterNames()
               .forEach(name -> addClusterWatcher(name));
           break;
         default:
-          Status error = Status.UNAVAILABLE.withDescription(
-              "unknown cluster type in " + resourceName() + " " + update.clusterType());
-          setDataAsStatus(error);
       }
-      maybePublishConfig();
     }
 
     public String getEdsServiceName() {
@@ -749,12 +725,6 @@ final class XdsDependencyManager implements XdsConfig.XdsClusterSubscriptionRegi
     }
 
     @Override
-    public void onChanged(XdsEndpointResource.EdsUpdate update) {
-      if (cancelled) {
-        return;
-      }
-      setData(checkNotNull(update, "update"));
-      maybePublishConfig();
-    }
+    public void subscribeToChildren(XdsEndpointResource.EdsUpdate update) {}
   }
 }