Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Web/Util/TaskExtensions.cs

@@ -0,0 +1,29 @@
+//------------------------------------------------------------------------------
+// <copyright file="TaskExtensions.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//------------------------------------------------------------------------------
+
+namespace System.Web.Util {
+    using System;
+    using System.Threading.Tasks;
+
+    // Contains helper methods for dealing with Tasks
+
+    internal static class TaskExtensions {
+
+        // Throws the exception that faulted a Task, similar to what 'await' would have done.
+        // Useful for synchronous methods which have a Task instance they know to be already completed
+        // and where they want to let the exception propagate upward.
+        public static void ThrowIfFaulted(this Task task) {
+            Debug.Assert(task.IsCompleted, "The Task passed to this method must be marked as completed so that this method doesn't block.");
+            task.GetAwaiter().GetResult();
+        }
+
+        // Gets a WithinCancellableCallbackTaskAwaiter from a Task.
+        public static WithinCancellableCallbackTaskAwaitable WithinCancellableCallback(this Task task, HttpContext context) {
+            return new WithinCancellableCallbackTaskAwaitable(context, task.GetAwaiter());
+        }
+
+    }
+}