done

Netch/3rd/DnsClient.NET/TaskExtensions.cs

@@ -0,0 +1,25 @@
+namespace System.Threading.Tasks
+{
+    internal static class TaskExtensions
+    {
+        public static async Task<T> WithCancellation<T>(this Task<T> task, CancellationToken cancellationToken, Action onCancel)
+        {
+            var tcs = new TaskCompletionSource<bool>();
+
+            using (cancellationToken.Register(s => ((TaskCompletionSource<bool>)s).TrySetResult(true), tcs))
+            {
+                if (task != await Task.WhenAny(task, tcs.Task).ConfigureAwait(false))
+                {
+                    try
+                    {
+                        onCancel();
+                    }
+                    catch { }
+                    throw new OperationCanceledException(cancellationToken);
+                }
+            }
+
+            return await task.ConfigureAwait(false);
+        }
+    }
+}