【redis】-使用Lua脚本解决多线程下的超卖问题以及为什么？

namespace MengLin.Shopping.Redis.LuaScript
{
    public class SecKillOriginal
    {

        static SecKillOriginal()
        {
            using (RedisClient client = new RedisClient("127.0.0.1", 6379))
            {
                //删除当前数据库中的所有Key, 默认删除的是db0
                client.FlushDb();
                //删除所有数据库中的key 
                client.FlushAll();

                //初始化库存数量为1和订单数量为0
                client.Set("inventoryNum", 1);
                client.Set("orderNum", 0);
            }
        }

        public static void Show()
        {
            for (int i = 0; i 3; i++)
            {
                Task.Run(() =>
                {
                    using (RedisClient client = new RedisClient("127.0.0.1", 6379))
                    {
                        int inventoryNum = client.Getint>("inventoryNum");
                        //如果库存数量大于0
                        if (inventoryNum > 0)
                        {
                            //给库存数量-1
                            var inventoryNum2 = client.Decr("inventoryNum");
                            Console.WriteLine($"给库存数量-1后的数量-inventoryNum: {inventoryNum2}");
                            //给订单数量+1
                            var orderNum = client.Incr("orderNum");
                            Console.WriteLine($"给订单数量+1后的数量-orderNum: {orderNum}");
                        }
                        else
                        {
                            Console.WriteLine($"抢购失败: 原因是因为没有库存");
                        }
                    }
                });
            }
        }
    }
}

namespace MengLin.Shopping.Redis.LuaScript
{
    public class SecKillLua
    {
        /// 

        /// 使用Lua脚本解决多线程下变卖的问题
        /// 
        static SecKillLua()
        {
            using (RedisClient client = new RedisClient("127.0.0.1", 6379))
            {
                //删除当前数据库中的所有Key, 默认删除的是db0
                client.FlushDb();
                //删除所有数据库中的key 
                client.FlushAll();

                //初始化库存数量为1和订单数量为0
                client.Set("inventoryNum", 1);
                client.Set("orderNum", 0);
            }
        }

        public static void Show()
        {
            for (int i = 0; i 3; i++)
            {
                Task.Run(() =>
                {
                    using (RedisClient client = new RedisClient("127.0.0.1", 6379))
                    {
                        //如果库存数量大于0，则给库存数量-1，给订单数量+1
                        var lua = @"local count = redis.call('get',KEYS[1])
                                        if(tonumber(count)>0)
                                        then
                                            --return count
                                            redis.call('INCR',ARGV[1])
                                            return redis.call('DECR',KEYS[1])
                                        else
                                            return -99
                                        end";
                        Console.WriteLine(client.ExecLuaAsString(lua, keys: new[] { "inventoryNum" }, args: new[] { "orderNum" }));
                    }
                });
            }
        }
    }
}