功能需求

使用 C# 编写一个 key-value 结构进程内缓存，实现数据的缓存操作，此处所用到的知识点如下：

线程安全的字典 ConcurrentDictionary；
设计模式之单例模式（Singleton）；
缓存数据【主动 & 被动】过期模式；

cache

key-value 缓存实现

说明：此处基于 .net 6 平台创建控制台项目。

新建 ConsoleApp 项目，添加 CustomCacheHelper.cs 类；

导入命名空间（namespace）

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

CustomCacheHelper.cs 类中编写实现方法

/// <summary>
/// 自定义内存缓存助手
/// </summary>
public sealed class CustomCacheHelper
{
    #region 单例模式
    //创建私有化静态obj锁  
    private static readonly object _ObjLock = new();
    //创建私有静态字段，接收类的实例化对象  
    private static volatile CustomCacheHelper? _Instance = null;
    //构造函数私有化  
    private CustomCacheHelper() { }
    //创建单利对象资源并返回  
    public static CustomCacheHelper GetSingleObj()
    {
        if (_Instance == null)
        {
            lock (_ObjLock)
            {
                if (_Instance == null)
                {
                    _Instance = new CustomCacheHelper();
                }
            }
        }
        return _Instance;
    }
    #endregion

    /// <summary>
    /// 缓存字典 => 【key|value|time】
    /// </summary>
    private static volatile ConcurrentDictionary<string, KeyValuePair<object, DateTime?>> _CacheDictionary = new();

    /// <summary>
    /// 1.主动过期
    /// </summary>
    static CustomCacheHelper()
    {
        Task.Run(() => {
            while (true)
            {
                int millisecondsTimeout = 1000 * 60 * 10;
                Thread.Sleep(millisecondsTimeout); //10分钟检查一次

                if (_CacheDictionary != null && _CacheDictionary.Keys.Count > 0)
                {
                    ICollection<string> listKey = _CacheDictionary.Keys;
                    foreach (var key in listKey)
                    {
                        var valueTime = _CacheDictionary[key];
                        if (valueTime.Value < DateTime.Now)
                        {
                            _CacheDictionary.TryRemove(key, out KeyValuePair<object, DateTime?> value);
                        }
                    }
                }
            }
        });
    }

    /// <summary>
    /// 索引器
    /// </summary>
    /// <param name="key"></param>
    /// <returns></returns>
    public object this[string key]
    {
        get => _CacheDictionary[key];
        set => _CacheDictionary[key] = new KeyValuePair<object, DateTime?>(value, null);
    }

    /// <summary>
    /// 设置相对过期缓存
    /// </summary>
    /// <param name="key">键</param>
    /// <param name="data">数据包</param>
    /// <param name="seconds">相对过期时间</param>
    public void Set(string key, object data, int seconds)
    {
        var expirationTime = DateTime.Now.AddSeconds(seconds);
        _CacheDictionary[key] = new KeyValuePair<object, DateTime?>(data, expirationTime);
    }

    /// <summary>
    /// 设置绝对过期缓存
    /// </summary>
    /// <param name="key">键<</param>
    /// <param name="data">数据包</param>
    public void Set(string key, object data)
    {
        this[key] = data; // 下面代码等效
        // _CacheDictionary[key] = new KeyValuePair<object, DateTime?>(data, null);
    }

    /// <summary>
    /// 通过key获取缓存value
    /// 2.被动过期
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="key"></param>
    /// <returns></returns>
    public T? Get<T>(string key)
    {
        if (Exist(key))
        {
            //var valueTime = _CacheDictionary[key];
            //return (T)valueTime.Key; //return (T)this[key];

            bool hasValue = _CacheDictionary.TryGetValue(key, out KeyValuePair<object, DateTime?> value);
            if (hasValue)
            {
                return (T)value.Key; //return (T)this[key];
            }
        }

        return default;
    }

    /// <summary>
    /// 获取所有的key
    /// </summary>
    /// <returns></returns>
    public ICollection<string> GetKeys() => _CacheDictionary.Keys;

    /// <summary>
    /// 获取缓存个数
    /// </summary>
    /// <returns></returns>
    public int Count()
    {
        int count = 0;
        if (_CacheDictionary != null)
        {
            count = _CacheDictionary.Count;
        }
        return count;
    }

    /// <summary>
    /// 删除指定key的value
    /// </summary>
    /// <param name="key"></param>
    public void Remove(string key)
    {
        if (Exist(key))
        {
            _CacheDictionary.TryRemove(key, out KeyValuePair<object, DateTime?> value);
        }
    }

    /// <summary>
    /// 清空所有缓存
    /// </summary>
    public void Cleaner()
    {
        if (_CacheDictionary != null && _CacheDictionary.Count > 0)
        {
            foreach (var key in _CacheDictionary.Keys)
            {
                _CacheDictionary.TryRemove(key, out KeyValuePair<object, DateTime?> value);
            }
        }
    }

    /// <summary>
    /// 2.被动过期，保证任何过期缓存都无法取值
    /// 检查key是否存在
    /// </summary>
    /// <param name="key"></param>
    /// <returns></returns>
    public bool Exist(string key)
    {
        bool isExist = false;
        if (!string.IsNullOrWhiteSpace(key) && _CacheDictionary.ContainsKey(key))
        {
            var valTime = _CacheDictionary[key];

            if (valTime.Value != null && valTime.Value > DateTime.Now)
            {
                isExist = true; //缓存没过期
            }
            else
            {
                if (valTime.Value == null)
                {
                    isExist = true; //永久缓存
                }
                else
                {
                    _CacheDictionary.TryRemove(key, out KeyValuePair<object, DateTime?> value); //缓存过期清理
                }
            }
        }
        return isExist;
    }
}

Main 方法使用缓存

由于该项目是采用控制台程序编写，我们可直接在 Main 方法中，添加如下代码：

var customCache = CustomCacheHelper.GetSingleObj();
customCache.Set("key1", "value1");
customCache.Set("key2", "value2", 3);
customCache.Set("key3", "value3", 6);
var keys = customCache.GetKeys();

Console.WriteLine("首次打印：");
foreach (var key in keys)
{
    Console.WriteLine($"time:{DateTime.Now},key={key},value={customCache.Get<string>(key)}");
}

Console.WriteLine("睡眠5s后再次打印：");
Thread.Sleep(5000);
foreach (var key in keys)
{
    Console.WriteLine($"time:{DateTime.Now},key={key},value={customCache.Get<string>(key)}");
}

此处代码中我们添加了三组 key-vaule 数据，其中一个是没有设置过期时间，另外两个设置过期时间，保存数据后，分别打印缓存中保存的数据，再第二次缓存打印前，先让线程睡眠等待 5 秒（5000毫秒），注意观察控制台输出的信息。

ConsoleApp 启动测试

从控制台输出的信息中，我们可以看到 key=key2 的 value 值为空，说明我们内部调用 Exist 方法生效了，key2 的 value 缓存有效时间是 3 秒，第二次打印输出信息时，此时已经睡眠 5 秒，相对于 key2 存储的内存数据已经超时，而 key3 的 value 存储的有效时间是 6 秒，没有超时，所以能个获取到对应的内存数据。