review comments

src/csharp/Grpc.Core.Api/ChannelBase.cs

@@ -68,9 +68,15 @@ namespace Grpc.Core
         }
 
         /// <summary>Provides implementation of a non-virtual public member.</summary>
-        protected virtual Task ShutdownAsyncCore()
+        #pragma warning disable 1998
+        protected virtual async Task ShutdownAsyncCore()
         {
-            throw new NotImplementedException();
+            // default implementation is no-op for backwards compatibility, but all implementations
+            // are expected to override this method.
+
+            // warning 1998 is disabled to avoid needing TaskUtils.CompletedTask, which is
+            // only available in Grpc.Core
         }
+        #pragma warning restore 1998
     }
 }

src/csharp/Grpc.Core/Channel.cs

@@ -210,18 +210,8 @@ namespace Grpc.Core
             }
         }
 
-        /// <summary>
-        /// Shuts down the channel cleanly. It is strongly recommended to shutdown
-        /// all previously created channels before exiting from the process.
-        /// </summary>
-        /// <remarks>
-        /// This method doesn't wait for all calls on this channel to finish (nor does
-        /// it explicitly cancel all outstanding calls). It is user's responsibility to make sure
-        /// all the calls on this channel have finished (successfully or with an error)
-        /// before shutting down the channel to ensure channel shutdown won't impact
-        /// the outcome of those remote calls.
-        /// </remarks>
-        public new async Task ShutdownAsync()
+        /// <summary>Provides implementation of a non-virtual public member.</summary>
+        protected override async Task ShutdownAsyncCore()
         {
             lock (myLock)
             {
@@ -246,13 +236,6 @@ namespace Grpc.Core
             await GrpcEnvironment.ReleaseAsync().ConfigureAwait(false);
         }
 
-        /// <summary>Provides implementation of a non-virtual public member.</summary>
-        protected override Task ShutdownAsyncCore()
-        {
-            // use the same behavior for ChannelBase.ShutdownAsync as for Channel.Shutdown()
-            return ShutdownAsync();
-        }
-
         /// <summary>
         /// Create a new <see cref="CallInvoker"/> for the channel.
         /// </summary>