//******************************************************************************************************//  TargetCache.cs - Gbtc////  Copyright © 2016, Grid Protection Alliance.  All Rights Reserved.////  Licensed to the Grid Protection Alliance (GPA) under one or more contributor license agreements. See//  the NOTICE file distributed with this work for additional information regarding copyright ownership.//  The GPA licenses this file to you under the MIT License (MIT), the "License"; you may//  not use this file except in compliance with the License. You may obtain a copy of the License at:////      http://opensource.org/licenses/MIT////  Unless agreed to in writing, the subject software distributed under the License is distributed on an//  "AS-IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. Refer to the//  License for the specific language governing permissions and limitations.////  Code Modification History://  ----------------------------------------------------------------------------------------------------//  10/02/2016 - J. Ritchie Carroll//       Generated original version of source code.////****************************************************************************************************** using System;using System.Collections.Generic;using System.Runtime.Caching;using System.Threading;using GSF.Threading; namespace GrafanaAdapters{    /// <summary>    /// Exposes a method to reinitialize sliding memory caches used by Grafana data sources.    /// </summary>    public static class TargetCaches    {        // References each type T instance TargetCache ResetCache function        internal static readonly List<Action> ResetCacheFunctions;         private static readonly ShortSynchronizedOperation s_resetAllCaches;         static TargetCaches()        {            ResetCacheFunctions = new();             s_resetAllCaches = new(() =>            {                Action[] resetCacheFunctions;                 lock (ResetCacheFunctions)                    resetCacheFunctions = ResetCacheFunctions.ToArray();                 foreach (Action resetCache in resetCacheFunctions)                    resetCache();            });        }         /// <summary>        /// Resets all sliding memory caches used by Grafana data sources.        /// </summary>        public static void ResetAll() =>             s_resetAllCaches.RunOnceAsync();    }     // Usage Note: Each type T should be unique unless cache can be safely shared    internal static class TargetCache<T>    {        // Desired use case is one static MemoryCache per type T:        // ReSharper disable StaticMemberInGenericType        private static readonly string s_cacheName;        private static MemoryCache s_targetCache;         static TargetCache()        {            s_cacheName = $"GrafanaTargetCache-{typeof(T).Name}";            s_targetCache = new(s_cacheName);             lock (TargetCaches.ResetCacheFunctions)                TargetCaches.ResetCacheFunctions.Add(ResetCache);        }         internal static T GetOrAdd(string target, Func<T> valueFactory)        {            Lazy<T> newValue = new(valueFactory);            Lazy<T> oldValue;             try            {                // Race condition exists here such that target cache being referenced may                // be disposed between access and method invocation - hence the try/catch                oldValue = s_targetCache.AddOrGetExisting(target, newValue, new CacheItemPolicy { SlidingExpiration = TimeSpan.FromMinutes(1.0D) }) as Lazy<T>;            }            catch            {                oldValue = null;            }             try            {                return (oldValue ?? newValue).Value;            }            catch            {                s_targetCache.Remove(target);                throw;            }        }         internal static void ResetCache() =>             Interlocked.Exchange(ref s_targetCache, new(s_cacheName)).Dispose();    }}