xds: run watcher callbacks in its own channel synchronization context (#7525)

In the context of sharing the XdsClient instance between Channels, watcher callbacks need to be executed in each Channel's own SynchronizationContext.

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

@@ -29,6 +29,7 @@ import io.grpc.LoadBalancer;
 import io.grpc.LoadBalancerProvider;
 import io.grpc.LoadBalancerRegistry;
 import io.grpc.Status;
+import io.grpc.SynchronizationContext;
 import io.grpc.internal.ObjectPool;
 import io.grpc.internal.ServiceConfigUtil.PolicySelection;
 import io.grpc.util.ForwardingLoadBalancerHelper;
@@ -52,6 +53,7 @@ import javax.annotation.Nullable;
 final class CdsLoadBalancer extends LoadBalancer {
   private final XdsLogger logger;
   private final Helper helper;
+  private final SynchronizationContext syncContext;
   private final LoadBalancerRegistry lbRegistry;
   private final TlsContextManager tlsContextManager;
   // TODO(sanjaypujare): remove once xds security is released
@@ -71,6 +73,7 @@ final class CdsLoadBalancer extends LoadBalancer {
   CdsLoadBalancer(Helper helper, LoadBalancerRegistry lbRegistry,
       TlsContextManager tlsContextManager) {
     this.helper = checkNotNull(helper, "helper");
+    this.syncContext = checkNotNull(helper.getSynchronizationContext(), "syncContext");
     this.lbRegistry = lbRegistry;
     this.tlsContextManager = tlsContextManager;
     logger = XdsLogger.withLogId(InternalLogId.allocate("cds-lb", helper.getAuthority()));
@@ -179,6 +182,7 @@ final class CdsLoadBalancer extends LoadBalancer {
 
   private final class CdsLbState implements CdsResourceWatcher {
     private final ChannelSecurityLbHelper lbHelper = new ChannelSecurityLbHelper();
+    private boolean shutdown;
     @Nullable
     LoadBalancer edsBalancer;
 
@@ -189,18 +193,22 @@ final class CdsLoadBalancer extends LoadBalancer {
     }
 
     @Override
-    public void onChanged(CdsUpdate newUpdate) {
+    public void onChanged(final CdsUpdate newUpdate) {
+      syncContext.execute(new Runnable() {
+        @Override
+        public void run() {
+          if (shutdown) {
+            return;
+          }
           if (logger.isLoggable(XdsLogLevel.INFO)) {
-        logger.log(
-            XdsLogLevel.INFO,
-            "Received cluster update from xDS client {0}: "
+            logger.log(XdsLogLevel.INFO, "Received cluster update from xDS client {0}: "
                     + "cluster_name={1}, eds_service_name={2}, lb_policy={3}, report_load={4}",
                 xdsClient, newUpdate.getClusterName(), newUpdate.getEdsServiceName(),
                 newUpdate.getLbPolicy(), newUpdate.getLrsServerName() != null);
           }
           // FIXME(chengyuanzhang): handle error correctly to avoid being unnecessarily fragile.
-      checkArgument(
-          newUpdate.getLbPolicy().equals("round_robin"), "can only support round_robin policy");
+          checkArgument(newUpdate.getLbPolicy().equals("round_robin"),
+              "can only support round_robin policy");
           LoadBalancerProvider endpointPickingPolicyProvider =
               lbRegistry.getProvider(newUpdate.getLbPolicy());
           LoadBalancerProvider localityPickingPolicyProvider =
@@ -221,6 +229,8 @@ final class CdsLoadBalancer extends LoadBalancer {
           edsBalancer.handleResolvedAddresses(
               resolvedAddresses.toBuilder().setLoadBalancingPolicyConfig(edsConfig).build());
         }
+      });
+    }
 
     /** For new UpstreamTlsContext value, release old SslContextProvider. */
     private void updateSslContextProviderSupplier(UpstreamTlsContext newUpstreamTlsContext) {
@@ -244,7 +254,13 @@ final class CdsLoadBalancer extends LoadBalancer {
     }
 
     @Override
-    public void onResourceDoesNotExist(String resourceName) {
+    public void onResourceDoesNotExist(final String resourceName) {
+      syncContext.execute(new Runnable() {
+        @Override
+        public void run() {
+          if (shutdown) {
+            return;
+          }
           logger.log(XdsLogLevel.INFO, "Resource {0} is unavailable", resourceName);
           if (edsBalancer != null) {
             edsBalancer.shutdown();
@@ -252,12 +268,20 @@ final class CdsLoadBalancer extends LoadBalancer {
           }
           helper.updateBalancingState(
               TRANSIENT_FAILURE,
-          new ErrorPicker(
-              Status.UNAVAILABLE.withDescription("Resource " + resourceName + " is unavailable")));
+              new ErrorPicker(Status.UNAVAILABLE.withDescription(
+                  "Resource " + resourceName + " is unavailable")));
+        }
+      });
     }
 
     @Override
-    public void onError(Status error) {
+    public void onError(final Status error) {
+      syncContext.execute(new Runnable() {
+        @Override
+        public void run() {
+          if (shutdown) {
+            return;
+          }
           logger.log(
               XdsLogLevel.WARNING,
               "Received error from xDS client {0}: {1}: {2}",
@@ -268,8 +292,11 @@ final class CdsLoadBalancer extends LoadBalancer {
             helper.updateBalancingState(TRANSIENT_FAILURE, new ErrorPicker(error));
           }
         }
+      });
+    }
 
     void shutdown() {
+      shutdown = true;
       xdsClient.cancelCdsResourceWatch(clusterName, this);
       logger.log(XdsLogLevel.INFO,
           "Cancelled watcher for cluster {0} with xDS client {1}", clusterName, xdsClient);

xds/src/main/java/io/grpc/xds/EdsLoadBalancer2.java

@@ -30,6 +30,7 @@ import io.grpc.LoadBalancer;
 import io.grpc.LoadBalancerProvider;
 import io.grpc.LoadBalancerRegistry;
 import io.grpc.Status;
+import io.grpc.SynchronizationContext;
 import io.grpc.internal.ObjectPool;
 import io.grpc.internal.ServiceConfigUtil.PolicySelection;
 import io.grpc.util.ForwardingLoadBalancerHelper;
@@ -60,6 +61,7 @@ import javax.annotation.Nullable;
 
 final class EdsLoadBalancer2 extends LoadBalancer {
   private final XdsLogger logger;
+  private final SynchronizationContext syncContext;
   private final LoadBalancerRegistry lbRegistry;
   private final ThreadSafeRandom random;
   private final GracefulSwitchLoadBalancer switchingLoadBalancer;
@@ -77,7 +79,8 @@ final class EdsLoadBalancer2 extends LoadBalancer {
       LoadBalancer.Helper helper, LoadBalancerRegistry lbRegistry, ThreadSafeRandom random) {
     this.lbRegistry = checkNotNull(lbRegistry, "lbRegistry");
     this.random = checkNotNull(random, "random");
-    switchingLoadBalancer = new GracefulSwitchLoadBalancer(checkNotNull(helper, "helper"));
+    syncContext = checkNotNull(helper, "helper").getSynchronizationContext();
+    switchingLoadBalancer = new GracefulSwitchLoadBalancer(helper);
     InternalLogId logId = InternalLogId.allocate("eds-lb", helper.getAuthority());
     logger = XdsLogger.withLogId(logId);
     logger.log(XdsLogLevel.INFO, "Created");
@@ -156,6 +159,7 @@ final class EdsLoadBalancer2 extends LoadBalancer {
       private ResolvedAddresses resolvedAddresses;
       private PolicySelection localityPickingPolicy;
       private PolicySelection endpointPickingPolicy;
+      private boolean shutdown;
       @Nullable
       private LoadBalancer lb;
 
@@ -216,6 +220,7 @@ final class EdsLoadBalancer2 extends LoadBalancer {
 
       @Override
       public void shutdown() {
+        shutdown = true;
         if (lrsServerName != null) {
           xdsClient.removeClientStats(cluster, edsServiceName);
         }
@@ -234,18 +239,23 @@ final class EdsLoadBalancer2 extends LoadBalancer {
       }
 
       @Override
-      public void onChanged(EdsUpdate update) {
+      public void onChanged(final EdsUpdate update) {
+        syncContext.execute(new Runnable() {
+          @Override
+          public void run() {
+            if (shutdown) {
+              return;
+            }
             logger.log(XdsLogLevel.DEBUG,
                 "Received endpoint update from xDS client {0}: {1}", xdsClient, update);
             if (logger.isLoggable(XdsLogLevel.INFO)) {
-          logger.log(
-              XdsLogLevel.INFO,
-              "Received endpoint update: cluster_name={0}, {1} localities, {2} drop categories",
-              update.getClusterName(), update.getLocalityLbEndpointsMap().size(),
-              update.getDropPolicies().size());
+              logger.log(XdsLogLevel.INFO, "Received endpoint update: cluster_name={0}, "
+                      + "{1} localities, {2} drop categories", update.getClusterName(),
+                  update.getLocalityLbEndpointsMap().size(), update.getDropPolicies().size());
             }
             lbHelper.updateDropPolicies(update.getDropPolicies());
-        Map<Locality, LocalityLbEndpoints> localityLbEndpoints = update.getLocalityLbEndpointsMap();
+            Map<Locality, LocalityLbEndpoints> localityLbEndpoints =
+                update.getLocalityLbEndpointsMap();
             endpointAddresses = new ArrayList<>();
             prioritizedLocalityWeights = new HashMap<>();
             for (Locality locality : localityLbEndpoints.keySet()) {
@@ -302,22 +312,40 @@ final class EdsLoadBalancer2 extends LoadBalancer {
                       .build());
             }
           }
-
-      @Override
-      public void onResourceDoesNotExist(String resourceName) {
-        logger.log(XdsLogLevel.INFO, "Resource {0} is unavailable", resourceName);
-        propagateResourceError(
-            Status.UNAVAILABLE.withDescription("Resource " + resourceName + " is unavailable"));
+        });
       }
 
       @Override
-      public void onError(Status error) {
+      public void onResourceDoesNotExist(final String resourceName) {
+        syncContext.execute(new Runnable() {
+          @Override
+          public void run() {
+            if (shutdown) {
+              return;
+            }
+            logger.log(XdsLogLevel.INFO, "Resource {0} is unavailable", resourceName);
+            propagateResourceError(Status.UNAVAILABLE.withDescription(
+                "Resource " + resourceName + " is unavailable"));
+          }
+        });
+      }
+
+      @Override
+      public void onError(final Status error) {
+        syncContext.execute(new Runnable() {
+          @Override
+          public void run() {
+            if (shutdown) {
+              return;
+            }
             logger.log(
                 XdsLogLevel.WARNING, "Received error from xDS client {0}: {1}", xdsClient, error);
             if (lb == null) {
               lbHelper.helper.updateBalancingState(TRANSIENT_FAILURE, new ErrorPicker(error));
             }
           }
+        });
+      }
 
       private void propagateResourceError(Status error) {
         if (lb != null) {

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

@@ -430,6 +430,7 @@ final class XdsNameResolver extends NameResolver {
             .setServiceConfig(emptyServiceConfig)
             // let channel take action for no config selector
             .build();
+    private boolean stopped;
     private Set<String> existingClusters;
     @Nullable
     private String rdsResource;
@@ -438,7 +439,13 @@ final class XdsNameResolver extends NameResolver {
     private long httpMaxStreamDurationNano;
 
     @Override
-    public void onChanged(LdsUpdate update) {
+    public void onChanged(final LdsUpdate update) {
+      syncContext.execute(new Runnable() {
+        @Override
+        public void run() {
+          if (stopped) {
+            return;
+          }
           logger.log(XdsLogLevel.INFO, "Receive LDS resource update: {0}", update);
           httpMaxStreamDurationNano = update.getHttpMaxStreamDurationNano();
           List<VirtualHost> virtualHosts = update.getVirtualHosts();
@@ -456,21 +463,39 @@ final class XdsNameResolver extends NameResolver {
             xdsClient.watchRdsResource(rdsResource, rdsWatcher);
           }
         }
+      });
+    }
 
     @Override
-    public void onError(Status error) {
+    public void onError(final Status error) {
+      syncContext.execute(new Runnable() {
+        @Override
+        public void run() {
+          if (stopped) {
+            return;
+          }
           logger.log(
               XdsLogLevel.WARNING,
               "Received error from xDS client {0}: {1}", xdsClient, error.getDescription());
           listener.onError(error);
         }
+      });
+    }
 
     @Override
-    public void onResourceDoesNotExist(String resourceName) {
+    public void onResourceDoesNotExist(final String resourceName) {
+      syncContext.execute(new Runnable() {
+        @Override
+        public void run() {
+          if (stopped) {
+            return;
+          }
           logger.log(XdsLogLevel.INFO, "LDS resource {0} unavailable", resourceName);
           cleanUpRdsWatcher();
           listener.onResult(emptyResult);
         }
+      });
+    }
 
     private void start() {
       logger.log(XdsLogLevel.INFO, "Start watching LDS resource {0}", authority);
@@ -479,6 +504,7 @@ final class XdsNameResolver extends NameResolver {
 
     private void stop() {
       logger.log(XdsLogLevel.INFO, "Stop watching LDS resource {0}", authority);
+      stopped = true;
       cleanUpRdsWatcher();
       xdsClient.cancelLdsResourceWatch(authority, this);
     }
@@ -550,23 +576,47 @@ final class XdsNameResolver extends NameResolver {
     private class RdsResourceWatcherImpl implements RdsResourceWatcher {
 
       @Override
-      public void onChanged(RdsUpdate update) {
+      public void onChanged(final RdsUpdate update) {
+        syncContext.execute(new Runnable() {
+          @Override
+          public void run() {
+            if (RdsResourceWatcherImpl.this != rdsWatcher) {
+              return;
+            }
             updateRoutes(update.getVirtualHosts());
           }
+        });
+      }
 
       @Override
-      public void onError(Status error) {
+      public void onError(final Status error) {
+        syncContext.execute(new Runnable() {
+          @Override
+          public void run() {
+            if (RdsResourceWatcherImpl.this != rdsWatcher) {
+              return;
+            }
             logger.log(
                 XdsLogLevel.WARNING,
                 "Received error from xDS client {0}: {1}", xdsClient, error.getDescription());
             listener.onError(error);
           }
+        });
+      }
 
       @Override
-      public void onResourceDoesNotExist(String resourceName) {
+      public void onResourceDoesNotExist(final String resourceName) {
+        syncContext.execute(new Runnable() {
+          @Override
+          public void run() {
+            if (RdsResourceWatcherImpl.this != rdsWatcher) {
+              return;
+            }
             logger.log(XdsLogLevel.INFO, "RDS resource {0} unavailable", resourceName);
             listener.onResult(emptyResult);
           }
+        });
+      }
     }
   }
 

xds/src/test/java/io/grpc/xds/CdsLoadBalancerTest.java

@@ -467,6 +467,11 @@ public class CdsLoadBalancerTest {
       throw new UnsupportedOperationException("should not be called");
     }
 
+    @Override
+    public SynchronizationContext getSynchronizationContext() {
+      return syncContext;
+    }
+
     @Deprecated
     @Override
     public NameResolver.Factory getNameResolverFactory() {