prevent race between grpcsharp_server_request_call and grpc_completion_queue_shutdown

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

@@ -53,9 +53,12 @@ namespace Grpc.Core.Internal
         }
 
         public void RegisterCompletionQueue(CompletionQueueSafeHandle cq)
+        {
+            using (cq.NewScope())
             {
                 Native.grpcsharp_server_register_completion_queue(this, cq);
             }
+        }
 
         public int AddInsecurePort(string addr)
         {
@@ -73,18 +76,24 @@ namespace Grpc.Core.Internal
         }
     
         public void ShutdownAndNotify(BatchCompletionDelegate callback, CompletionQueueSafeHandle completionQueue)
+        {
+            using (completionQueue.NewScope())
             {
                 var ctx = BatchContextSafeHandle.Create();
                 completionQueue.CompletionRegistry.RegisterBatchCompletion(ctx, callback);
                 Native.grpcsharp_server_shutdown_and_notify_callback(this, completionQueue, ctx);
             }
+        }
 
         public void RequestCall(BatchCompletionDelegate callback, CompletionQueueSafeHandle completionQueue)
+        {
+            using (completionQueue.NewScope())
             {
                 var ctx = BatchContextSafeHandle.Create();
                 completionQueue.CompletionRegistry.RegisterBatchCompletion(ctx, callback);
                 Native.grpcsharp_server_request_call(this, completionQueue, ctx).CheckOk();
             }
+        }
 
         protected override bool ReleaseHandle()
         {