add "state" filed to batch completion delegate

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

@@ -21,6 +21,7 @@ using System.Runtime.InteropServices;
 using System.Text;
 using Grpc.Core;
 using Grpc.Core.Logging;
+using Grpc.Core.Utils;
 
 namespace Grpc.Core.Internal
 {
@@ -37,6 +38,8 @@ namespace Grpc.Core.Internal
         static readonly NativeMethods Native = NativeMethods.Get();
         static readonly ILogger Logger = GrpcEnvironment.Logger.ForType<BatchContextSafeHandle>();
 
+        CompletionCallbackData completionCallbackData;
+
         private BatchContextSafeHandle()
         {
         }
@@ -54,7 +57,12 @@ namespace Grpc.Core.Internal
             }
         }
 
-        public BatchCompletionDelegate CompletionCallback { get; set; }
+        public void SetCompletionCallback(BatchCompletionDelegate callback, object state)
+        {
+            GrpcPreconditions.CheckState(completionCallbackData.Callback == null);
+            GrpcPreconditions.CheckNotNull(callback, nameof(callback));
+            completionCallbackData = new CompletionCallbackData(callback, state);
+        }
 
         // Gets data of recv_initial_metadata completion.
         public Metadata GetReceivedInitialMetadata()
@@ -106,7 +114,7 @@ namespace Grpc.Core.Internal
         {
             try
             {
-                CompletionCallback(success, this);
+                completionCallbackData.Callback(success, this, completionCallbackData.State);
             }
             catch (Exception e)
             {
@@ -114,9 +122,21 @@ namespace Grpc.Core.Internal
             }
             finally
             {
-                CompletionCallback = null;
+                completionCallbackData = default(CompletionCallbackData);
                 Dispose();
             }
         }
+
+        struct CompletionCallbackData
+        {
+            public CompletionCallbackData(BatchCompletionDelegate callback, object state)
+            {
+                this.Callback = callback;
+                this.State = state;
+            }
+
+            public BatchCompletionDelegate Callback { get; }
+            public object State { get; }
+        }
     }
 }

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

@@ -25,7 +25,7 @@ using Grpc.Core.Utils;
 
 namespace Grpc.Core.Internal
 {
-    internal delegate void BatchCompletionDelegate(bool success, BatchContextSafeHandle ctx);
+    internal delegate void BatchCompletionDelegate(bool success, BatchContextSafeHandle ctx, object state);
 
     internal delegate void RequestCallCompletionDelegate(bool success, RequestCallContextSafeHandle ctx);
 
@@ -53,9 +53,9 @@ namespace Grpc.Core.Internal
             }
         }
 
-        public void RegisterBatchCompletion(BatchContextSafeHandle ctx, BatchCompletionDelegate callback)
+        public void RegisterBatchCompletion(BatchContextSafeHandle ctx, BatchCompletionDelegate callback, object state)
         {
-            ctx.CompletionCallback = callback;
+            ctx.SetCompletionCallback(callback, state);
             Register(ctx.Handle, ctx);
         }