LocalAppContext.cs

using System.Collections.Generic;
using System.Reflection;
using System.Runtime.CompilerServices;

namespace System
{
    internal static 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;

        private static readonly object s_syncLock;

        private static bool DisableCaching
        {
            get;
            set;
        }

        static LocalAppContext()
        {
            s_switchMap = new Dictionary<string, bool>();
            s_syncLock = new object();
            s_canForwardCalls = SetupDelegate();
            System.AppContextDefaultValues.PopulateDefaultValues();
            DisableCaching = IsSwitchEnabled("TestSwitch.LocalAppContext.DisableCaching");
        }

        public static bool IsSwitchEnabled(string switchName)
        {
            if (s_canForwardCalls && TryGetSwitchFromCentralAppContext(switchName, out bool value))
            {
                return value;
            }
            return IsSwitchEnabledLocal(switchName);
        }

        private static bool IsSwitchEnabledLocal(string switchName)
        {
            bool flag;
            bool value;
            lock (s_switchMap)
            {
                flag = s_switchMap.TryGetValue(switchName, out value);
            }
            if (flag)
            {
                return value;
            }
            return false;
        }

        private static bool SetupDelegate()
        {
            Type type = typeof(object).Assembly.GetType("System.AppContext");
            if (type == null)
            {
                return false;
            }
            MethodInfo method = type.GetMethod("TryGetSwitch", BindingFlags.Static | BindingFlags.Public, null, new Type[2]
            {
                typeof(string),
                typeof(bool).MakeByRefType()
            }, null);
            if (method == null)
            {
                return false;
            }
            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 (DisableCaching)
            {
                return IsSwitchEnabled(switchName);
            }
            bool flag = IsSwitchEnabled(switchName);
            switchValue = (flag ? 1 : (-1));
            return flag;
        }

        internal static void DefineSwitchDefault(string switchName, bool initialValue)
        {
            s_switchMap[switchName] = initialValue;
        }
    }
}