Imported Upstream version 4.0.0~alpha1

Former-commit-id: 806294f5ded97629b74c85c09952f2a74fe182d9

external/referencesource/System.Runtime.Serialization/System/Runtime/Serialization/AppSettings.cs

@@ -0,0 +1,63 @@
+// <copyright>
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+
+namespace System.Runtime.Serialization
+{
+    using System;
+    using System.Collections.Specialized;
+    using System.Configuration;
+    using System.Diagnostics.CodeAnalysis;
+    using System.Security.Permissions;
+
+    static class AppSettings
+    {
+        internal const string MaxMimePartsAppSettingsString = "microsoft:xmldictionaryreader:maxmimeparts";
+        const int DefaultMaxMimeParts = 1000;
+        static int maxMimeParts;
+        static volatile bool settingsInitalized = false;
+        static object appSettingsLock = new object();
+
+        internal static int MaxMimeParts
+        {
+            get
+            {
+                EnsureSettingsLoaded();
+
+                return maxMimeParts;
+            }
+        }
+
+        [SuppressMessage(FxCop.Category.ReliabilityBasic, "Reliability104:CaughtAndHandledExceptionsRule", 
+            Justification = "Handle the configuration exceptions here to avoid regressions on customer's existing scenarios")]
+        static void EnsureSettingsLoaded()
+        {
+            if (!settingsInitalized)
+            {
+                lock (appSettingsLock)
+                {
+                    if (!settingsInitalized)
+                    {
+                        NameValueCollection appSettingsSection = null;
+                        try
+                        {
+                            appSettingsSection = ConfigurationManager.AppSettings;
+                        }
+                        catch (ConfigurationErrorsException)
+                        {
+                        }
+                        finally
+                        {
+                            if ((appSettingsSection == null) || !int.TryParse(appSettingsSection[MaxMimePartsAppSettingsString], out maxMimeParts))
+                            {
+                                maxMimeParts = DefaultMaxMimeParts;
+                            }
+
+                            settingsInitalized = true;
+                        }
+                    }
+                }
+            }
+        }
+    }
+}