add a repro and fix for grpc#19090

src/csharp/Grpc.Core.Tests/CallAfterShutdownTest.cs

@@ -0,0 +1,48 @@
+#region Copyright notice and license
+
+// Copyright 2020 The gRPC Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System;
+using NUnit.Framework;
+
+namespace Grpc.Core.Tests
+{
+    public class CallAfterShutdownTest
+    {
+        Method<string, string> dummyUnaryMethod = new Method<string, string>(MethodType.Unary, "fooservice", "dummyMethod", Marshallers.StringMarshaller, Marshallers.StringMarshaller);
+
+        [Test]
+        public void StartBlockingUnaryCallAfterChannelShutdown()
+        {
+            // create a channel and immediately shut it down.
+            var channel = new Channel("127.0.0.1", 1000, ChannelCredentials.Insecure);
+            channel.ShutdownAsync().Wait();  // also shuts down GrpcEnvironment
+
+            Assert.Throws(typeof(ObjectDisposedException), () => Calls.BlockingUnaryCall(new CallInvocationDetails<string, string>(channel, dummyUnaryMethod, new CallOptions()), "THE REQUEST"));
+        }
+
+        [Test]
+        public void StartAsyncUnaryCallAfterChannelShutdown()
+        {
+            // create a channel and immediately shut it down.
+            var channel = new Channel("127.0.0.1", 1000, ChannelCredentials.Insecure);
+            channel.ShutdownAsync().Wait();  // also shuts down GrpcEnvironment
+
+            Assert.Throws(typeof(ObjectDisposedException), () => Calls.AsyncUnaryCall(new CallInvocationDetails<string, string>(channel, dummyUnaryMethod, new CallOptions()), "THE REQUEST"));
+        }
+    }
+}

src/csharp/Grpc.Core/Internal/AsyncCall.cs

@@ -78,7 +78,12 @@ public TResponse UnaryCall(TRequest msg)
             var profiler = Profilers.ForCurrentThread();
 
             using (profiler.NewScope("AsyncCall.UnaryCall"))
-            using (CompletionQueueSafeHandle cq = CompletionQueueSafeHandle.CreateSync())
+
+            // Create a pluckable completion queue for the call. Avoid creating a completion queue when we know the channel has already
+            // been shutdown. In such case, the call will fail with ObjectDisposedException immediately anyway and creating / destroying
+            // a completion queue would lead to crash if this was the last channel in the application (and thus GrpcEnvironment has been shutdown).
+            // See https://github.com/grpc/grpc/issues/19090
+            using (CompletionQueueSafeHandle cq = details.Channel.Handle.IsClosed ?  null : CompletionQueueSafeHandle.CreateSync())
             {
                 bool callStartedOk = false;
                 try

src/csharp/tests.json

@@ -22,6 +22,7 @@
     "Grpc.Core.Tests.AppDomainUnloadTest",
     "Grpc.Core.Tests.AuthContextTest",
     "Grpc.Core.Tests.AuthPropertyTest",
+    "Grpc.Core.Tests.CallAfterShutdownTest",
     "Grpc.Core.Tests.CallCancellationTest",
     "Grpc.Core.Tests.CallCredentialsTest",
     "Grpc.Core.Tests.CallOptionsTest",