.Net Core缓存组件(MemoryCache)【缓存篇（二）】

 public void ConfigureServices(IServiceCollection services)
        {
            //添加内存缓存
            services.AddMemoryCache();
        }

 #region 注入缓存
        private readonly IMemoryCache Cache;
        public MemoryCacheController(IMemoryCache cache)
        {
            Cache = cache;
        }
        #endregion

            //设置缓存  当我们没有指定过期时间，理论是永久的（后面会说到不理论的）
            Cache.Set("key", "value");
            Console.WriteLine(Cache.Get("key"));

            //设置缓存绝对过期时间
            Cache.Set("key1", "value", new DateTimeOffset(new DateTime(2020, 7, 22)));
            Console.WriteLine(Cache.Get("key1"));

            //设置相对过期时间
            Cache.Set("key2", "value", new TimeSpan(0, 0, 10));
            Console.WriteLine(Cache.Get("key2"));

            //设置滑动过期时间
            Cache.Set("key3", "value", new MemoryCacheEntryOptions()
            {
                //设置滑动过期
                SlidingExpiration = new TimeSpan(0, 0, 5),
                //设置缓存的优先级，当我们缓存空间不足的时候会移除等级低的缓存，以此类推（清除的时候不会管是否过期）
                //Low,    低的意思
                //Normal, 正常模式  默认模式
                //High,   高
                //NeverRemove 绝不回收，这个就算内存满了也不会清除。
                Priority = CacheItemPriority.NeverRemove
            });
            Console.WriteLine(Cache.Get("key3"));

Cache.GetOrCreate("key4", cacheEntry =>
            {
                //设置滑动过期
                cacheEntry.SlidingExpiration= new TimeSpan(0, 0, 5);
                //设置删除回调函数
                cacheEntry.RegisterPostEvictionCallback(CallbackFunction);
                //设置内存
                return cacheEntry.Value = "滑动过期时间带删除回调";
            });
            Thread.Sleep(2000);
            Console.WriteLine(Cache.Get("key4"));
            Thread.Sleep(4000);
            Console.WriteLine(Cache.Get("key4"));
            Thread.Sleep(5000);

/// 

        /// 删除回调函数
        /// 
        /// 
        /// 
        /// 
        /// 
        public void CallbackFunction(object key, object value, EvictionReason reason, object state)
        {
            Console.WriteLine($"你被删除了key：{key},value：{value}回调函数");
        }

            ////CreateEntry设置缓存
            var entity = Cache.CreateEntry("key5");
            entity.Value = "5555";
            Console.WriteLine("CreateEntry 获取信息：" + Cache.Get("key5"));  //结果null

 //方法1
            var entity = Cache.CreateEntry("key5");
            entity.Value = "5555";
            entity.Dispose();
            Console.WriteLine("CreateEntry 获取信息：" + Cache.Get("key5"));  //结果5555

            //方法2
            using (var entity = Cache.CreateEntry("key5"))
            {
                entity.Value = "5555";
                Console.WriteLine("CreateEntry 获取信息：" + Cache.Get("key5"));  //结果5555
            }

public void Dispose()
{
      if (!_added)
      {
          _added = true;
          _scope.Dispose();
          _notifyCacheEntryDisposed(this);//在此调用委托，而此委托是被MemoryCache类中的SetEntry赋值。目的是将CacheEntry实体放入MemoryCache类的字典中，也就是放入缓存中。
          PropagateOptions(CacheEntryHelper.Current);
      

        /// 

        /// Adds a non distributed in memory implementation of  to the
        /// .
        /// 
        /// The  to add services to.
        /// The  so that additional calls can be chained.
        public static IServiceCollection AddMemoryCache(this IServiceCollection services)
        {
            if (services == null)
            {
                throw new ArgumentNullException(nameof(services));
            }

            services.AddOptions();
            services.TryAdd(ServiceDescriptor.Singleton());

            return services;
        }

            //添加内存缓存
            services.AddMemoryCache(x=> {
                x.CompactionPercentage = 0.05;//缓存压缩大小
                x.ExpirationScanFrequency= new TimeSpan(0, 0, 1); //默认自动扫描时间为三分钟
                x.SizeLimit = 500 * 1024 * 1024; //大小为500M
            });

private void StartScanForExpiredItems()//扫描函数。在添加、查找、删除、修改缓存的时候，会调用此方法扫描过滤过期缓存，并不是主动隔一段时间执行
        {
            var now = _clock.UtcNow;
            if (_expirationScanFrequency //判断现在的时间和最后一次扫描时间，是不是大于设置的时间段
            {
                _lastExpirationScan = now;
                Task.Factory.StartNew(state => ScanForExpiredItems((MemoryCache)state), this, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
            }
        }
        private static void ScanForExpiredItems(MemoryCache cache)
        {
            var now = cache._clock.UtcNow;
            foreach (var entry in cache._entries.Values)//然后遍历字典集合，移除过期缓存
            {
                if (entry.CheckExpired(now))
                {
                    cache.RemoveEntry(entry);
                }
            }
        }