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