Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Xml/System/Xml/Serialization/AppSettings.cs

@@ -0,0 +1,55 @@
+//------------------------------------------------------------------------------
+// <copyright file="AppSettings.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//------------------------------------------------------------------------------
+
+namespace System.Xml.Serialization {
+    using System;
+    using System.Collections.Specialized;
+    using System.Configuration;
+    using System.Diagnostics.CodeAnalysis;
+    using System.Security.Permissions;
+
+    internal static class AppSettings {
+        private const string UseLegacySerializerGenerationAppSettingsString = "System:Xml:Serialization:UseLegacySerializerGeneration";
+        private static bool? useLegacySerializerGeneration;
+        private static volatile bool settingsInitalized = false;
+        private static object appSettingsLock = new object();
+
+        internal static bool? UseLegacySerializerGeneration {
+            get {
+                EnsureSettingsLoaded();
+                return useLegacySerializerGeneration;
+            }
+        }
+
+        static void EnsureSettingsLoaded() {
+#if CONFIGURATION_DEP
+            if (!settingsInitalized) {
+                lock (appSettingsLock) {
+                    if (!settingsInitalized) {
+                        NameValueCollection appSettingsSection = null;
+                        try {
+                            appSettingsSection = ConfigurationManager.AppSettings;
+                        }
+                        catch (ConfigurationErrorsException) {
+                        }
+                        finally {
+                            bool tempUseLegacySerializerGeneration;
+                            if ((appSettingsSection == null) || !bool.TryParse(appSettingsSection[UseLegacySerializerGenerationAppSettingsString], out tempUseLegacySerializerGeneration)) {
+                                useLegacySerializerGeneration = null;
+                            } 
+                            else {
+                                useLegacySerializerGeneration = (bool?)tempUseLegacySerializerGeneration;
+                            }
+
+                            settingsInitalized = true;
+                        }
+                    }
+                }
+            }
+#endif
+        }
+    }
+}