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c# 理解csredis实现分布式锁

作者:互联网

声明:

这里首先使用的是csredis,地址是https://github.com/2881099/csredis

该库本身已经足够完善,这里我画蛇添足一下,为了方便自己的使用。

本身csredis库已经实现了完整的加锁和去锁的逻辑,这里实现的与库本身所实现的有以下几点区别(csredis实现代码位置为:https://github.com/2881099/csredis/blob/bb6d947695770333027f3936f80052041db41b64/src/CSRedisCore/CSRedisClient.cs#L4344,有兴趣可以去了解看下)

1. 去掉了csredis的锁续租部分的功能,尽量简化

2. 将锁的token的设定交给外部,使用guid也罢,使用id也行。通过已知的token,保证了你可以在任意地方以观察者的身份释放锁。

3. 尽量不修改其key的原本值,不添加前缀,防止在观测时出现不必要的麻烦。

 

逻辑:

加锁就是set 一个 key ,如果key 存在的情况下则返回失败。那么典型的命令就是setnx.

一个锁显然是需要一个过期时间的,那么我们可能要用到 expire命令。

释放锁则是一个del命令

查看锁的值是需要get命令

比较常见的加锁使用的是setnx,不过由于redis支持了SET key token NX EX/PX max-lock-time(sec/millsec) (设置key token 是否不存在才set 秒数模式/毫秒数模式  秒数或毫秒数) 这种传参模式,由此,这里更加推荐使用set 命令。

如果在我们的代码端执行del 则小概率发生以下情况:

  A 申请锁set  x,过期时间为t。

  经过时间t后,A恰好忙完了,A通过get命令看看token是否一致,得到结果发现一致的。

       A决定发送del到redis服务器,此时A恰好网络拥堵。

       redis服务器由于锁x超时,进而释放了锁x。

  此时B恰好也申请了锁x,无过期时间。

       A网络恢复,del命令发送成功。

       结果 B的锁被A释放了。

幸好redis支持了lua脚本。让我们得以简单的实现过期,加锁,去锁功能,而不需要自己手动timer过期。

这里要使用到eval命令执行脚本。

代码

using CSRedis;
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;

namespace CsRedis.Helper
{
    /// <summary>
    ///  基于csredis的简单封装
    /// </summary>
    public class CsRedisManager
    {
       
        private ConcurrentDictionary<string, CSRedisClient> _serviceNameWithClient;
      
        /// <summary>
        ///  初始化
        /// </summary>
        public void Init()
        {
            _serviceNameWithClient = new ConcurrentDictionary<string, CSRedisClient>();
        }

        /// <summary>
        ///  获取业务redis服务
        /// </summary>
        /// <param name="serviceName"></param>
        /// <returns></returns>
        public CSRedisClient GetRedisClient(string serviceName)
        {
            CSRedisClient result = null;
            _serviceNameWithClient.TryGetValue(serviceName,out result);

            return result;
        }

        /// <summary>
        ///  添加redis服务
        /// </summary>
        /// <param name="serviceName"></param>
        /// <param name="connectStr"></param>
        /// <returns></returns>
        public bool AddRedisClient(string serviceName,string connectStr)
        {
            CSRedisClient cSRedisClient = new CSRedisClient(connectStr);
            return _serviceNameWithClient.TryAdd(serviceName, cSRedisClient);
        }

        /// <summary>
        ///  设置字符串型kv 
        /// </summary>
        /// <param name="key">key</param>
        /// <param name="value">value</param>
        /// <param name="expireSecond">过期时间(秒)</param>
        /// <returns>是否成功</returns>
        public bool Set(string serviceName,string key,string value,int expireSecond=-1)
        {
            var redisClient = GetRedisClient(serviceName);
            GetExceptionOfClient(redisClient);
            
            return redisClient.Set(key, value, expireSecond);
           
        }

        /// <summary>
        ///  获取相应key的值
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        public string Get(string serviceName, string key)
        {
            var redisClient = GetRedisClient(serviceName);
            GetExceptionOfClient(redisClient);
            
            return redisClient.Get(key);
            
           
        }

        /// <summary>
        ///  如果不存在则执行,存在则忽略
        /// </summary>
        /// <param name="serviceName"></param>
        /// <param name="key"></param>
        /// <param name="value"></param>
        /// <returns></returns>
        public bool SetNx(string serviceName, string key, string value)
        {
            var redisClient = GetRedisClient(serviceName);
            GetExceptionOfClient(redisClient);

            var res = redisClient.SetNx(key, value);
            return res;
        }

        /// <summary>
        ///  带过期时间的setNx
        /// </summary>
        /// <param name="serviceName"></param>
        /// <param name="key"></param>
        /// <param name="value"></param>
        /// <param name="seconds"></param>
        /// <returns></returns>
        public bool SetNx(string serviceName, string key, string value, int millSeconds = -1)
        {
            var res = Set(serviceName, key, value, RedisExistence.Nx, millSeconds);

            return res;
        }

        /// <summary>
        ///  带过期时间的SetXx
        /// </summary>
        /// <param name="serviceName"></param>
        /// <param name="key"></param>
        /// <param name="value"></param>
        /// <param name="seconds"></param>
        /// <returns></returns>
        public bool SetXx(string serviceName, string key, string value, int millSeconds = -1)
        {
            var res = Set(serviceName, key, value, RedisExistence.Xx, millSeconds);

            return res;
        }

        /// <summary>
        ///  带参数set
        /// </summary>
        /// <param name="serviceName"></param>
        /// <param name="key"></param>
        /// <param name="value"></param>
        /// <param name="existence"></param>
        /// <param name="seconds"></param>
        /// <returns></returns>
        public bool Set(string serviceName, string key, string value, RedisExistence existence, int millSeconds = -1)
        {
            var redisClient = GetRedisClient(serviceName);
            GetExceptionOfClient(redisClient);

            var res = redisClient.Set(key, value, millSeconds, existence);

            return res;
        }

        /// <summary>
        ///  设置生存时间
        /// </summary>
        /// <param name="serviceName"></param>
        /// <param name="key"></param>
        /// <param name="seconds"></param>
        /// <returns></returns>
        public bool Expire(string serviceName, string key, int seconds)
        {
            var redisClient = GetRedisClient(serviceName);
            GetExceptionOfClient(redisClient);

            return redisClient.Expire(key, seconds);
        }

        /// <summary>
        ///  获取剩余的生存时间(秒)
        /// </summary>
        /// <param name="serviceName"></param>
        /// <param name="key"></param>
        /// <returns></returns>
        public long Ttl(string serviceName, string key)
        {
            var redisClient = GetRedisClient(serviceName);
            GetExceptionOfClient(redisClient);

            return redisClient.Ttl(key);
        }

        /// <summary>
        ///  删除del
        /// </summary>
        /// <param name="serviceName"></param>
        /// <param name="key"></param>
        /// <returns></returns>
        public long Del(string serviceName,params string[] keys)
        {
            var redisClient = GetRedisClient(serviceName);
            GetExceptionOfClient(redisClient);

            
            return redisClient.Del(keys);
        }

        /// <summary>
        ///  执行脚本
        /// </summary>
        /// <param name="serviceName"></param>
        /// <param name="script"></param>
        /// <param name="key"></param>
        /// <param name="args"></param>
        /// <returns></returns>
        public object Eval(string serviceName, string script,string key,params object[] args)
        {
            var redisClient = GetRedisClient(serviceName);
            GetExceptionOfClient(redisClient);

            var res = redisClient.Eval(script, key,args);

            return res;
        }

        /// <summary>
        ///  添加共享锁
        /// </summary>
        /// <param name="serviceName"></param>
        /// <param name="key"></param>
        /// <param name="seconds"></param>
        /// <returns></returns>
        public bool AddLock(string serviceName, string key,string token, int millSeconds = -1)
        {
            var valRes = SetNx(serviceName, key, token, millSeconds);

            return valRes;
        }

        /// <summary>
        ///  删除共享锁
        /// </summary>
        /// <param name="serviceName"></param>
        /// <param name="key"></param>
        /// <returns></returns>
        public bool ReleaseLock(string serviceName, string key,string token)
        {
            var script = GetReleaseLockScript();

            var redisClient = GetRedisClient(serviceName);
            GetExceptionOfClient(redisClient);

            var res = redisClient.Eval(script, key, token);

            if (0== (long)res)
            {
                return false;
            }
            return true;
            
        }

        /// <summary>
        ///  获取键值
        /// </summary>
        /// <param name="serviceName"></param>
        /// <param name="pattern"></param>
        /// <returns></returns>
        public string[] Keys(string serviceName, string pattern)
        {
            var redisClient = GetRedisClient(serviceName);
            GetExceptionOfClient(redisClient);
            var res = redisClient.Keys(pattern);

            return res;
        }

        /// <summary>
        ///  获取client发生异常
        /// </summary>
        /// <param name="client"></param>
        private void GetExceptionOfClient(CSRedisClient client)
        {
            if (client == null)
            {
                throw new Exception("无有效的redis服务");
            }
        }


        /// <summary>
        ///  lua脚本删除共享锁
        ///  解决在A申请锁 xxkey  过期的瞬间,B 申请锁xxkey,
        ///  此时恰好A执行到释放xxkey从而引起的异常释放
        /// </summary>
        /// <returns></returns>
        private static  string GetReleaseLockScript()
        {
            return "if redis.call(\"get\",KEYS[1]) == ARGV[1] \nthen\nreturn redis.call(\"del\", KEYS[1])\nelse\nreturn 0\nend";
        }

        
    }

    
}

这里我把要单独执行的lua脚本单独提出来

if redis.call("get",KEYS[1]) == ARGV[1]
then
    return redis.call("del",KEYS[1])
else
    return 0
end

这段脚本对应的是c# 中的  GetReleaseLockScript()方法中的文字。

这里我个人偷了个懒,按照道理,这里应该有个LoadScriptPath,加载脚本所在位置,调用的时候先检查脚本是否在内存中,不在则去LoadScriptPath找对应的脚本,方便不同的人协同合作。不过那个就是脚本管理器了,还要设计interface,有点偏离主题了。

 

下面是测试代码

using CsRedis.Helper;
using NUnit.Framework;

namespace TestProject
{
    public class Tests
    {
        [SetUp]
        public void Setup()
        {
        }

        [Test]
        public void Test1()
        {
            CsRedisManager csRedisManager = new CsRedisManager();
            csRedisManager.Init();
            csRedisManager.AddRedisClient("TEST", "127.0.0.1:6379,password=123456, connectTimeout =1000,connectRetry=1,syncTimeout=10000,defaultDatabase=0");
            //csRedisManager.AddRedisClient("PRODUCT", "127.0.0.1:6379,password=123456, connectTimeout =1000,connectRetry=1,syncTimeout=10000,defaultDatabase=1");
            

            var token = "123";
            var lockKey = "LOCKKEY1";

            csRedisManager.AddLock("TEST", lockKey,token,20 * 1000);
            csRedisManager.ReleaseLock("TEST", lockKey, token);

            
        }
    }
}

这里就是对于共享锁的一点简单实现,多了挺多与本次的命令无关的代码,海涵海涵

 

标签:string,c#,redisClient,csredis,serviceName,key,var,public,分布式
来源: https://www.cnblogs.com/lsnct/p/15866860.html