C#緩存初步學習

1. 緩存是什麼，各級緩存

2. 本地緩存原理和實現

3. 緩存應用和緩存更新

 

緩存：爲了快速獲取結果，在第一次獲取數據後存起來，下次直接使用

緩存通常用在哪裏？

1. 會重複的請求

2. 數據相對穩定

3. 耗時/耗資源

4. 體積不大

配置文件；菜單-權限；省市區；類別數據；

熱搜；公告；技能/屬性；數據字典；

分頁(只要數據不是常常變)

若是一個數據緩存一次，可以被有效查詢4次，那這個緩存就是值得的(大型系統的時候，爲了性能，爲了壓力，須要更多的緩存)

緩存自己是共享的，因此每一個緩存應該是惟一的

 

本地緩存空間小，不能跨進程共享

小項目通常隨便緩存

中大型項目不夠用的，通常就會使用分佈式緩存

 

如：

Memcached:內存管理

Redis: REmote DIctionary Server

 

下面附上我學習使用的自建簡單Cahce緩存代碼：

 

public class CustomeCache
    {
        /// <summary>
        /// 線程安全的Dictionary集合
        /// </summary>
        public static Dictionary<string, KeyValuePair<object, DateTime>> CustomCacheDictionary;

        /// <summary>
        /// 緩存須要自動清理:防止過多無用緩存
        /// </summary>
        static CustomeCache()
        {
            CustomCacheDictionary = new Dictionary<string, KeyValuePair<object, DateTime>>();
            Console.WriteLine($"{DateTime.Now.ToString("MM-dd HH:mm:ss fff")}初始化緩存");
            Task.Run(() =>
            {
                while (true)
                {
                    LockAction(new Action(() => {
                        List<string> list = new List<string>();
                        foreach (var key in CustomCacheDictionary.Keys)
                        {
                            var valueTime = CustomCacheDictionary[key];
                            if (valueTime.Value > DateTime.Now)
                            {
                                //沒有過時就不用管
                            }
                            else {
                                //過時就統一將key放入list中
                                list.Add(key);
                            }
                        }
                        list.ForEach(key => CustomCacheDictionary.Remove(key));
                    }));
                    Thread.Sleep(1000 * 60 * 15);//每15分鐘清理一次
                }
            });
        }

        private static readonly object CustomCache_Lock = new object();
        public static void LockAction(Action action)
        {
            lock (CustomCache_Lock)
            {
                action.Invoke();
            }
        }

        /// <summary>
        /// 添加緩存數據
        /// </summary>
        /// <param name="key"></param>
        /// <param name="value"></param>
        /// <param name="second"></param>
        public static void Add(string key, object value, int second = 1800) {
            LockAction(new Action(() =>
            {
                CustomCacheDictionary.Add(key, new KeyValuePair<object, DateTime>(value, DateTime.Now.AddSeconds(second)));
            }));
        }

        /// <summary>
        /// 保存數據  -存在則更新 不存在則新增
        /// </summary>
        /// <param name="key"></param>
        /// <param name="value"></param>
        /// <param name="second"></param>
        public static void SaveOrUpdate(string key, object value, int second = 1800) {
            LockAction(new Action(() =>
            {
                CustomCacheDictionary[key] = new KeyValuePair<object, DateTime>(value, DateTime.Now.AddSeconds(second));
            }));
        }

        public static T Find<T>(string key, Func<T> func, int second = 1800) {
            T t = default(T);
            if (!Exsit(key))
            {
                t = func.Invoke();
                CustomeCache.Add(key, t, second);
            }
            else {
                t = Get<T>(key);
            }
            return t;
        }

        /// <summary>
        /// 獲取數據 沒有則異常
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="key"></param>
        /// <returns></returns>
        public static T Get<T>(string key) {
            return (T)CustomCacheDictionary[key].Key;
        }

        /// <summary>
        /// 檢查是否存在
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        public static bool Exsit(string key)
        {
            if (CustomCacheDictionary.ContainsKey(key))
            {
                var valueTime = CustomCacheDictionary[key];
                if (valueTime.Value > DateTime.Now)
                {   //時候未到
                    return true;
                }
                else {
                    //時晨已到  上臺
                    LockAction(new Action(() =>
                    {
                        CustomCacheDictionary.Remove(key);
                    }));
                    return false;
                }
            }
            else {
                return false;
            }
        }

        public static void Remove(string key) {
            LockAction(new Action(() =>
            {
                CustomCacheDictionary.Remove(key);
            }));
        }
                
        public static void RemoveAll() {
            LockAction(new Action(() =>
            {
                CustomCacheDictionary.Clear();
            }));
        }

        public static void RemoveCondition(Func<string, bool> func) {
            LockAction(new Action(() =>
            {
                List<string> list = new List<string>();
                foreach (var key in CustomCacheDictionary.Keys)
                {
                    if (func.Invoke(key))
                    {
                        list.Add(key);
                    }
                }
                list.ForEach(key => CustomCacheDictionary.Remove(key));
            }));
        }

    }