Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

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

@@ -0,0 +1,73 @@
+//------------------------------------------------------------------------------
+// <copyright file="SynchronizationContextUtil.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//------------------------------------------------------------------------------
+
+namespace System.Web.Util {
+    using System;
+    using System.Web;
+
+    internal static class SynchronizationContextUtil {
+
+        public static SynchronizationContextMode CurrentMode {
+            get {
+                return (!AppSettings.UseTaskFriendlySynchronizationContext) ? SynchronizationContextMode.Legacy : SynchronizationContextMode.Normal;
+            }
+        }
+
+        private static string FormatErrorMessage(string specificErrorMessage, SynchronizationContextMode requiredMode) {
+            // The output of this function will be a message like this:
+            // "What you're trying to do is unsupported. Follow these steps to resolve it. For more
+            // info, see this URL."
+
+            string resolutionMessage;
+            if (HttpRuntime.TargetFramework < VersionUtil.Framework45 && requiredMode == SynchronizationContextMode.Normal) {
+                // upgrade to 4.5 mode
+                resolutionMessage = SR.SynchronizationContextUtil_UpgradeToTargetFramework45Instructions;
+            }
+            else if (HttpRuntime.TargetFramework >= VersionUtil.Framework45 && requiredMode == SynchronizationContextMode.Legacy) {
+                // already in 4.5 mode, add the back-compat switch
+                resolutionMessage = SR.SynchronizationContextUtil_AddDowngradeAppSettingsSwitch;
+            }
+            else {
+                // remove the <appSettings> switch
+                resolutionMessage = SR.SynchronizationContextUtil_RemoveAppSettingsSwitch;
+            }
+
+            return SR.GetString(specificErrorMessage)
+                + " " + SR.GetString(resolutionMessage)
+                + "\r\n" + SR.GetString(SR.SynchronizationContextUtil_ForMoreInformation);
+        }
+
+        public static void ValidateMode(SynchronizationContextMode currentMode, SynchronizationContextMode requiredMode, string specificErrorMessage) {
+            Debug.Assert(specificErrorMessage != null);
+            if (currentMode != requiredMode) {
+                string errorMessage = FormatErrorMessage(specificErrorMessage, requiredMode);
+                throw new InvalidOperationException(errorMessage);
+            }
+        }
+
+        public static void ValidateModeForAspCompat() {
+            ValidateMode(
+                currentMode: CurrentMode,
+                requiredMode: SynchronizationContextMode.Legacy,
+                specificErrorMessage: SR.SynchronizationContextUtil_AspCompatModeNotCompatible);
+        }
+
+        public static void ValidateModeForPageAsyncVoidMethods() {
+            ValidateMode(
+                currentMode: CurrentMode,
+                requiredMode: SynchronizationContextMode.Normal,
+                specificErrorMessage: SR.SynchronizationContextUtil_PageAsyncVoidMethodsNotCompatible);
+        }
+
+        public static void ValidateModeForWebSockets() {
+            ValidateMode(
+                currentMode: CurrentMode,
+                requiredMode: SynchronizationContextMode.Normal,
+                specificErrorMessage: SR.SynchronizationContextUtil_WebSocketsNotCompatible);
+        }
+
+    }
+}