Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

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

@@ -0,0 +1,33 @@
+//------------------------------------------------------------------------------
+// <copyright file="DisposableAction.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>                                                                
+//------------------------------------------------------------------------------
+
+namespace System.Web.Util {
+    using System;
+    using System.Threading;
+
+    // Helper class for wrapping a continuation inside an IDisposable.
+    // This class is thread-safe.
+
+    internal sealed class DisposableAction : IDisposable {
+
+        public static readonly DisposableAction Empty = new DisposableAction(null);
+
+        private Action _disposeAction;
+
+        public DisposableAction(Action disposeAction) {
+            _disposeAction = disposeAction;
+        }
+
+        public void Dispose() {
+            // Interlocked allows the continuation to be executed only once
+            Action continuation = Interlocked.Exchange(ref _disposeAction, null);
+            if (continuation != null) {
+                continuation();
+            }
+        }
+
+    }
+}