rls: Avoid missed config update from reentrancy (v1.77.x backport)

rls/src/main/java/io/grpc/rls/LbPolicyConfiguration.java

@@ -248,10 +248,10 @@ ChildPolicyWrapper createOrGet(String target) {
       RefCountedChildPolicyWrapper pooledChildPolicyWrapper = childPolicyMap.get(target);
       if (pooledChildPolicyWrapper == null) {
         ChildPolicyWrapper childPolicyWrapper = new ChildPolicyWrapper(
-            target, childPolicy, childLbResolvedAddressFactory, childLbHelperProvider,
-            childLbStatusListener);
+            target, childPolicy, childLbHelperProvider, childLbStatusListener);
         pooledChildPolicyWrapper = RefCountedChildPolicyWrapper.of(childPolicyWrapper);
         childPolicyMap.put(target, pooledChildPolicyWrapper);
+        childPolicyWrapper.start(childLbResolvedAddressFactory);
         return pooledChildPolicyWrapper.getObject();
       } else {
         ChildPolicyWrapper childPolicyWrapper = pooledChildPolicyWrapper.getObject();
@@ -298,7 +298,6 @@ static final class ChildPolicyWrapper {
     public ChildPolicyWrapper(
         String target,
         ChildLoadBalancingPolicy childPolicy,
-        final ResolvedAddressFactory childLbResolvedAddressFactory,
         ChildLoadBalancerHelperProvider childLbHelperProvider,
         ChildLbStatusListener childLbStatusListener) {
       this.target = target;
@@ -313,6 +312,9 @@ public ChildPolicyWrapper(
       this.childLbConfig = lbConfig.getConfig();
       helper.getChannelLogger().log(
           ChannelLogLevel.DEBUG, "RLS child lb created. config: {0}", childLbConfig);
+    }
+
+    void start(ResolvedAddressFactory childLbResolvedAddressFactory) {
       helper.getSynchronizationContext().execute(
           new Runnable() {
             @Override

rls/src/test/java/io/grpc/rls/LbPolicyConfigurationTest.java

@@ -21,6 +21,7 @@
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
@@ -45,8 +46,8 @@
 import io.grpc.rls.LbPolicyConfiguration.ChildPolicyWrapper.ChildPolicyReportingHelper;
 import io.grpc.rls.LbPolicyConfiguration.InvalidChildPolicyConfigException;
 import io.grpc.rls.LbPolicyConfiguration.RefCountedChildPolicyWrapperFactory;
-import java.lang.Thread.UncaughtExceptionHandler;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicBoolean;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -61,6 +62,9 @@ public class LbPolicyConfigurationTest {
   private final LoadBalancer lb = mock(LoadBalancer.class);
   private final SubchannelStateManager subchannelStateManager = new SubchannelStateManagerImpl();
   private final SubchannelPicker picker = mock(SubchannelPicker.class);
+  private final SynchronizationContext syncContext = new SynchronizationContext((t, e) -> {
+    throw new AssertionError(e);
+  });
   private final ChildLbStatusListener childLbStatusListener = mock(ChildLbStatusListener.class);
   private final ResolvedAddressFactory resolvedAddressFactory =
       new ResolvedAddressFactory() {
@@ -84,15 +88,7 @@ public ResolvedAddresses create(Object childLbConfig) {
   @Before
   public void setUp() {
     doReturn(mock(ChannelLogger.class)).when(helper).getChannelLogger();
-    doReturn(
-        new SynchronizationContext(
-            new UncaughtExceptionHandler() {
-              @Override
-              public void uncaughtException(Thread t, Throwable e) {
-                throw new AssertionError(e);
-              }
-            }))
-        .when(helper).getSynchronizationContext();
+    doReturn(syncContext).when(helper).getSynchronizationContext();
     doReturn(lb).when(lbProvider).newLoadBalancer(any(Helper.class));
     doReturn(ConfigOrError.fromConfig(new Object()))
         .when(lbProvider).parseLoadBalancingPolicyConfig(ArgumentMatchers.<Map<String, ?>>any());
@@ -190,4 +186,22 @@ public void updateBalancingState_triggersListener() {
     // picker governs childPickers will be reported to parent LB
     verify(helper).updateBalancingState(ConnectivityState.READY, picker);
   }
+
+  @Test
+  public void refCountedGetOrCreate_addsChildBeforeConfiguringChild() {
+    AtomicBoolean calledAlready = new AtomicBoolean();
+    when(lb.acceptResolvedAddresses(any(ResolvedAddresses.class))).thenAnswer(i -> {
+      if (!calledAlready.get()) {
+        calledAlready.set(true);
+        // Should end up calling this function again, as this child should already be added to the
+        // list of children. In practice, this can be caused by CDS is_dynamic=true starting a watch
+        // when XdsClient already has the cluster cached (e.g., from another channel).
+        syncContext.execute(() ->
+            factory.acceptResolvedAddressFactory(resolvedAddressFactory));
+      }
+      return Status.OK;
+    });
+    ChildPolicyWrapper unused = factory.createOrGet("foo.google.com");
+    verify(lb, times(2)).acceptResolvedAddresses(any(ResolvedAddresses.class));
+  }
 }