Merge branch 'sauravzg-feat-cached-channel' into ext-proc

# Conflicts:
#	xds/src/main/java/io/grpc/xds/internal/grpcservice/CachedChannelManager.java
#	xds/src/test/java/io/grpc/xds/internal/grpcservice/CachedChannelManagerTest.java

Author: kannanjgithub

xds/src/main/java/io/grpc/xds/internal/grpcservice/CachedChannelManager.java

@@ -19,6 +19,7 @@
 import static com.google.common.base.Preconditions.checkNotNull;
 
 import com.google.auto.value.AutoValue;
+import com.google.common.annotations.VisibleForTesting;
 import io.grpc.ManagedChannel;
 import io.grpc.xds.internal.grpcservice.GrpcServiceConfig.GoogleGrpcConfig;
 import java.util.concurrent.atomic.AtomicReference;
@@ -32,6 +33,7 @@ public class CachedChannelManager {
   private final Object lock = new Object();
 
   private final AtomicReference<ChannelHolder> channelHolder = new AtomicReference<>();
+  private boolean closed;
 
   /**
    * Default constructor for production that creates a channel using the config's target and
@@ -48,6 +50,7 @@ public CachedChannelManager() {
   /**
    * Constructor for testing to inject a channel creator.
    */
+  @VisibleForTesting
   public CachedChannelManager(Function<GrpcServiceConfig, ManagedChannel> channelCreator) {
     this.channelCreator = checkNotNull(channelCreator, "channelCreator");
   }
@@ -73,6 +76,9 @@ public ManagedChannel getChannel(GrpcServiceConfig config) {
 
     // 2. Slow path: Update with locking
     synchronized (lock) {
+      if (closed) {
+        throw new IllegalStateException("CachedChannelManager is closed");
+      }
       holder = channelHolder.get(); // Double check
       if (holder != null && holder.channelKey().equals(newChannelKey)) {
         return holder.channel();
@@ -98,9 +104,12 @@ public ManagedChannel getChannel(GrpcServiceConfig config) {
 
   /** Removes underlying resources on shutdown. */
   public void close() {
-    ChannelHolder holder = channelHolder.get();
-    if (holder != null) {
-      holder.channel().shutdown();
+    synchronized (lock) {
+      closed = true;
+      ChannelHolder holder = channelHolder.getAndSet(null);
+      if (holder != null) {
+        holder.channel().shutdown();
+      }
     }
   }
 

xds/src/test/java/io/grpc/xds/internal/grpcservice/CachedChannelManagerTest.java

@@ -68,15 +68,15 @@ public void setUp() {
   private GrpcServiceConfig buildConfig(String target, String credsType) {
     ChannelCredsConfig credsConfig = mock(ChannelCredsConfig.class);
     when(credsConfig.type()).thenReturn(credsType);
-    
+
     ConfiguredChannelCredentials creds = ConfiguredChannelCredentials.create(
         mock(io.grpc.ChannelCredentials.class), credsConfig);
-        
+
     GoogleGrpcConfig googleGrpc = GoogleGrpcConfig.builder()
         .target(target)
         .configuredChannelCredentials(creds)
         .build();
-        
+
     return GrpcServiceConfig.builder()
         .googleGrpc(googleGrpc)
         .initialMetadata(ImmutableList.of())
@@ -120,4 +120,44 @@ public void close_shutsDownChannel() {
 
     verify(mockChannel1).shutdown();
   }
+
+  @Test
+  public void getChannel_afterClose_throwsException() {
+    when(mockCreator.apply(config1)).thenReturn(mockChannel1);
+
+    manager.getChannel(config1);
+    manager.close();
+
+    try {
+      manager.getChannel(config1);
+      org.junit.Assert.fail("Expected IllegalStateException");
+    } catch (IllegalStateException e) {
+      assertThat(e).hasMessageThat().contains("CachedChannelManager is closed");
+    }
+  }
+
+  @Test
+  public void constructor_defaultCreatesChannel() {
+    CachedChannelManager defaultManager = new CachedChannelManager();
+    io.grpc.ChannelCredentials creds = io.grpc.InsecureChannelCredentials.create();
+    ChannelCredsConfig credsConfig = mock(ChannelCredsConfig.class);
+    when(credsConfig.type()).thenReturn("insecure");
+    ConfiguredChannelCredentials configuredCreds =
+        ConfiguredChannelCredentials.create(creds, credsConfig);
+    GoogleGrpcConfig googleGrpc = GoogleGrpcConfig.builder()
+        .target("localhost:8080")
+        .configuredChannelCredentials(configuredCreds)
+        .build();
+    GrpcServiceConfig config = GrpcServiceConfig.builder()
+        .googleGrpc(googleGrpc)
+        .initialMetadata(ImmutableList.of())
+        .build();
+
+    ManagedChannel channel = defaultManager.getChannel(config);
+    assertThat(channel).isNotNull();
+    
+    channel.shutdownNow();
+    defaultManager.close();
+  }
+
 }