139 lines
5.4 KiB
C#
139 lines
5.4 KiB
C#
// ==++==
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//
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// Copyright (c) Microsoft Corporation. All rights reserved.
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//
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// ==--==
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// There are cases where we have multiple assemblies that are going to import this file and
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// if they are going to also have InternalsVisibleTo between them, there will be a compiler warning
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// that the type is found both in the source and in a referenced assembly. The compiler will prefer
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// the version of the type defined in the source
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//
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// In order to disable the warning for this type we are disabling this warning for this entire file.
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#pragma warning disable 436
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// NOTE: This file should not be included in mscorlib. This should only be included in FX libraries that need to provide switches
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using System;
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using System.Collections.Generic;
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using System.Reflection;
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using System.Runtime.CompilerServices;
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using System.Threading;
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namespace System
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{
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internal static partial class LocalAppContext
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{
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private delegate bool TryGetSwitchDelegate(string switchName, out bool value);
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private static TryGetSwitchDelegate TryGetSwitchFromCentralAppContext;
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private static bool s_canForwardCalls;
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private static Dictionary<string, bool> s_switchMap = new Dictionary<string, bool>();
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private static readonly object s_syncLock = new object();
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private static bool DisableCaching { get; set; }
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static LocalAppContext()
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{
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// Try to setup the callback into the central AppContext
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s_canForwardCalls = SetupDelegate();
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// Populate the default values of the local app context
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AppContextDefaultValues.PopulateDefaultValues();
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// Cache the value of the switch that help with testing
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DisableCaching = IsSwitchEnabled(@"TestSwitch.LocalAppContext.DisableCaching");
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}
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public static bool IsSwitchEnabled(string switchName)
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{
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if (s_canForwardCalls)
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{
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bool isEnabledCentrally;
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if (TryGetSwitchFromCentralAppContext(switchName, out isEnabledCentrally))
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{
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// we found the switch, so return whatever value it has
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return isEnabledCentrally;
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}
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// if we could not get the value from the central authority, try the local storage.
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}
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return IsSwitchEnabledLocal(switchName);
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}
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private static bool IsSwitchEnabledLocal(string switchName)
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{
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// read the value from the set of local defaults
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bool isEnabled, isPresent;
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lock (s_switchMap)
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{
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isPresent = s_switchMap.TryGetValue(switchName, out isEnabled);
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}
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// If the value is in the set of local switches, reutrn the value
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if (isPresent)
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{
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return isEnabled;
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}
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// if we could not find the switch name, we should return 'false'
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// This will preserve the concept of switches been 'off' unless explicitly set to 'on'
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return false;
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}
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private static bool SetupDelegate()
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{
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Type appContextType = typeof(object).Assembly.GetType("System.AppContext");
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if (appContextType == null)
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return false;
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MethodInfo method = appContextType.GetMethod(
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"TryGetSwitch", // the method name
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BindingFlags.Static | BindingFlags.Public, // binding flags
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null, // use the default binder
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new Type[] { typeof(string), typeof(bool).MakeByRefType() },
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null); // parameterModifiers - this is ignored by the default binder
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if (method == null)
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return false;
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// Create delegate if we found the method.
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TryGetSwitchFromCentralAppContext = (TryGetSwitchDelegate)Delegate.CreateDelegate(typeof(TryGetSwitchDelegate), method);
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return true;
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}
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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internal static bool GetCachedSwitchValue(string switchName, ref int switchValue)
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{
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if (switchValue < 0) return false;
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if (switchValue > 0) return true;
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return GetCachedSwitchValueInternal(switchName, ref switchValue);
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}
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private static bool GetCachedSwitchValueInternal(string switchName, ref int switchValue)
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{
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if (LocalAppContext.DisableCaching)
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{
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return LocalAppContext.IsSwitchEnabled(switchName);
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}
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bool isEnabled = LocalAppContext.IsSwitchEnabled(switchName);
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switchValue = isEnabled ? 1 /*true*/ : -1 /*false*/;
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return isEnabled;
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}
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/// <summary>
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/// This method is going to be called from the AppContextDefaultValues class when setting up the
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/// default values for the switches. !!!! This method is called during the static constructor so it does not
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/// take a lock !!!! If you are planning to use this outside of that, please ensure proper locking.
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/// </summary>
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internal static void DefineSwitchDefault(string switchName, bool initialValue)
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{
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s_switchMap[switchName] = initialValue;
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}
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}
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}
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#pragma warning restore 436
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