using System;

using System.Linq;

using System.Runtime.Caching;

using System.Threading;

using System.Threading.Tasks;

​

namespace MemoryCacheLockingPattern

{

    public class Program

    {

        /// <summary>

        /// 快取 Key 值

        /// </summary>

        const string CacheKey = "cacheKey";

​

        /// <summary>

        /// Main Program

        /// </summary>

        /// <param name="args">The Arguments</param>

        public static void Main(string[] args)

        {

            var credential = string.Empty;

​

            Parallel.ForEach(Enumerable.Range(0, 100), (value) =>

            {

                // Cache 時間︰1 秒

                credential = MemoryCacheHelper.GetCachedData<string>(CacheKey, 1, GenereateCredential);

                Console.WriteLine(credential);

            });

​

            Console.ReadLine();

        }

​

        /// <summary>

        /// 產生憑証檔的方法

        /// </summary>

        /// <returns>憑証</returns>

        private static string GenereateCredential()

        {

            Console.WriteLine("產生憑証檔...");

​

            // 假設產生憑証檔需時 200ms

            Thread.Sleep(200);

​

            return "憑証";

        }

    }

​

    /// <summary>

    /// Memory Cache Helper

    /// </summary>

    public static class MemoryCacheHelper

    {

        /// <summary>

        /// Cache Lock

        /// </summary>

        private static object CacheLock = "cacheLock";

​

        /// <summary>

        /// 取得快取內容

        /// </summary>

        /// <typeparam name="T">資料型別</typeparam>

        /// <param name="cacheKey">快取 Key 值</param>

        /// <param name="expiredSeconds">快取到期時間</param>

        /// <param name="DataGenerator"></param>

        /// <returns>快取內容</returns>

        public static T GetCachedData<T>(string cacheKey, int expiredSeconds, Func<T> GetData) where T : class

        {

            T cachedData = MemoryCache.Default.Get(cacheKey, null) as T;

​

            // Cache Hit

            if (cachedData != null)

            {

                return cachedData;

            }

​

            lock (CacheLock)

            {

                // 再取一次 cache 確定仍然沒有需要的資料

                cachedData = MemoryCache.Default.Get(cacheKey, null) as T;

​

                // Cache Hit

                if (cachedData != null)

                {

                    return cachedData;

                }

​

                // Cache Miss

                cachedData = GetData();

                CacheItemPolicy policy = new CacheItemPolicy()

                {

                    AbsoluteExpiration = new DateTimeOffset(DateTime.Now.AddSeconds(expiredSeconds))

                };

                MemoryCache.Default.Set(cacheKey, cachedData, policy);

            }

​

            return cachedData;

        }

    }

}

​