EF+SQLSERVER控制并发下抢红包减余额（改进）

最近几年想必大家一听到哪里有抢红包可以抢，马上会拿起手机点去~~~~然后问题来了。。。

如何控制在同一时间保证数据库中扣减红包余额不会出错。之前我们的做法是直接锁程序，这样子带来的坏处就是等待时间太长，每当一个线程进去之后要经过以下几个过程。

过程分别是

1. 查表

2. 校验信息

3. 发送微信服务器

4. 等待反馈

5. 更新表

等这些过程结束之后才轮到下面这个过程。想必这样要等到花儿都谢了~

另外发送微信服务器这个过程时间在0s至9s时间不等。会产生大量的空闲时间，这里CPU会产生大量的空闲。而且这种情况也无法继续做负载均衡，如果有多个站点部署必定会产生数据库并发问题。

若在查表之前加锁更新后释放掉，虽然说不会产生数据库并发。但是在第二个线程进入查询的时候他会一直在等待，其耗时则与更锁程序差不多。

改进

这个想法源于分布式事务的设计，采用预扣红包余额的方式来保证无需等待微信服务器反馈，让下一个线程可继续执行相关任务。当微信服务器反馈回来时，才开始另外一个事务去更改交易状态。若反馈结果为FAIL则需要预扣的红包余额进行还原操作。

粗略写了模拟实际环境的测试代码，模拟抢红包动作

private void task()
{
    for (int i = ; i < ; i++)
    {
        string tradeNo = Qxun.Framework.Utility.CreateOrderNo.DateTimeAndNumber();
        try
        {
            using (var trans = new TransactionScope())
            {
                using (var dbContext = new ActivityDbContext())
                {
                    //加锁
                    var model = dbContext.Database.SqlQuery<Qxun.Activity.Contract.VIPPassRedBag013>(@"select * from VIPPassRedBag013 with(updlock) where ActivitySceneID=199").FirstOrDefault();
                    var mode = dbContext.Database.SqlQuery<Qxun.Activity.Contract.VIPPassRedBag013Mode>(@"select * from VIPPassRedBag013Mode with(updlock) where ActivitySceneID=199").ToList();
                    //模拟校验延迟
                    Thread.Sleep();
                    //得到领取红包的金额
                    VIPPassRedBag013Mode currentMode = null;
                    foreach (var modeItem in mode)
                    {
                        if (modeItem.RemainCount > )
                        {
                            currentMode = modeItem;
                            break;
                        }
                    }
                    //判断是否领完
                    if (currentMode != null && model != null && model.RedBagBalance >= currentMode.Money)
                    {
                        VIPPassRedBag013Play currentPlayModel = new VIPPassRedBag013Play();//本次的参与记录对象
                        currentPlayModel.VIPPassRedBag013ModeID = currentMode.ID;
                        currentPlayModel.WeixinUserID = Thread.CurrentThread.ManagedThreadId;
                        currentPlayModel.Money = Convert.ToInt32(currentMode.Money * );//要支付的金额（存入到表的）
                        currentPlayModel.TradeNumber = tradeNo;
                        currentPlayModel.Status = (int)TradeStatus.Trading;
                        currentPlayModel.VIPPassRedBag013ModeID = currentMode.ID;
                        currentPlayModel.ActivitySceneID = ;
                        dbContext.Insert<VIPPassRedBag013Play>(currentPlayModel);
                        currentMode.RemainCount -= ;
                        dbContext.Update<VIPPassRedBag013Mode>(currentMode);
                        model.RedBagBalance -= currentMode.Money;
                        dbContext.Update<Qxun.Activity.Contract.VIPPassRedBag013>(model);
                        trans.Complete();

                    }
                    else
                    {
                        trans.Complete();
                    }
                }
            }
        }
        catch (Exception ex){}
        //提交至微信
        string returnCode = "SUCCESS";
        Random ran = new Random();
        int time = ran.Next();
        if (time <= )
        {
            returnCode = "FAIL";
        }
        //模拟网络延迟
        Thread.Sleep(time * );
        //设置重新尝试次数
        bool retry = true;
        int retryCount = ;
        do
        {
            Qxun.Activity.Contract.VIPPassRedBag013 model = null;
            VIPPassRedBag013Play playModel = null;
            VIPPassRedBag013Mode mode = null;
            try
            {
                using (var trans = new TransactionScope())
                {
                    using (var dbContext = new ActivityDbContext())
                    {
                        //这里获取很容易异常
                        model = dbContext.Database.SqlQuery<Qxun.Activity.Contract.VIPPassRedBag013>(@"select * from VIPPassRedBag013 with(updlock) where ActivitySceneID=199").FirstOrDefault();
                        playModel = dbContext.Database.SqlQuery<Qxun.Activity.Contract.VIPPassRedBag013Play>(@"select * from VIPPassRedBag013Play with(updlock) where TradeNumber='" + tradeNo + "'").FirstOrDefault();
                        mode = dbContext.Database.SqlQuery<Qxun.Activity.Contract.VIPPassRedBag013Mode>(@"select * from VIPPassRedBag013Mode with(updlock) where ID=" + playModel.VIPPassRedBag013ModeID).FirstOrDefault();
                        if (returnCode == "SUCCESS")
                        {
                            playModel.Status = (int)TradeStatus.Success;
                            playModel.Remark = "retry=" + retryCount + ",success;time=" + DateTime.Now.ToString();
                            playModel.FinishTime = DateTime.Now;
                            dbContext.Update<VIPPassRedBag013Play>(playModel);
                            trans.Complete();
                            retry = false;
                        }
                        else
                        {
                            model.RedBagBalance += mode.Money;
                            dbContext.Update<Qxun.Activity.Contract.VIPPassRedBag013>(model);
                            playModel.Status = (int)TradeStatus.Fail;
                            playModel.Remark = "retry=" + retryCount + ",fail;time=" + DateTime.Now.ToString();
                            playModel.FinishTime = DateTime.Now;
                            dbContext.Update<VIPPassRedBag013Play>(playModel);
                            mode.RemainCount += ;
                            dbContext.Update<VIPPassRedBag013Mode>(mode);
                            trans.Complete();
                            retry = false;
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                //如果之前的线程请求数据库时阻塞
                //如果执行失败
                retryCount++;
                retry = true;
            }
            if (retryCount > )
            {
                break;
            }
        } while (retry);
    }
}

模拟100个人并发抢红包

public ActionResult Excute()
{
    for (int i = ; i < ; i++)
    {
        Thread thread = new Thread(new ThreadStart(task));
        thread.Start();
    }
    return Content("完成！");
}

上面代码还用了一个retry变量控制防止由于长等待产生的超时，好让每个订单都能够处理的到。但是实际上当线程数量为100-200时候，会有10至20个VIPPassRedBag013Play订单状态一直为Trading。当线程数量大于200的时候就变得及不稳定，目前一直没有找到是什么原因。希望有缘人指点一二。

为了解决这种现象，我在Global写了周期去查找10分钟前的VIPPassRedBag013Play，且订单状态为Trading的单子（都10分钟了还没有处理，那就是处理不到了）。得到订单号，去反查微信的红包交易记录。通过微信红包反馈的结果去更新数据库的交易状态。

public ActionResult Check()
{
    using (var dbContext = new ActivityDbContext())
    {
        //查询十分钟之前状态仍为交易中的订单
        var playModel = dbContext.Database
            .SqlQuery<Qxun.Activity.Contract.VIPPassRedBag013Play>(@"select * from VIPPassRedBag013Play with(nolock) where ActivitySceneID=199 and[status] = 2 and DATEDIFF(MINUTE, CreateTime, GETDATE()) > 10").ToList();
        if (playModel != null && playModel.Count > )
        {
            foreach (var item in playModel)
            {
                using (var trans = new TransactionScope())
                {
                    //提交至微信查询
                    string returnCode = "SUCCESS";
                    Random ran = new Random();
                    int time = ran.Next();
                    if (time <= )
                    {
                        returnCode = "FAIL";
                    }
                    //去查询微信红包的信息
                    //模拟网络延迟
                    Thread.Sleep(time * );
                    if (returnCode == "SUCCESS")
                    {
                        item.Status = (int)TradeStatus.Success;
                        item.Remark = "success;time=" + DateTime.Now.ToString();
                        item.FinishTime = DateTime.Now;
                        dbContext.Update<VIPPassRedBag013Play>(item);
                        trans.Complete();
                    }
                    else
                    {
                        Qxun.Activity.Contract.VIPPassRedBag013 model = dbContext.Database
                            .SqlQuery<Qxun.Activity.Contract.VIPPassRedBag013>(@"select * from VIPPassRedBag013 with(updlock) where ActivitySceneID=199")
                            .FirstOrDefault();
                        VIPPassRedBag013Mode mode = dbContext.Database
                            .SqlQuery<Qxun.Activity.Contract.VIPPassRedBag013Mode>(@"select * from VIPPassRedBag013Mode with(updlock) where ID=" + item.VIPPassRedBag013ModeID).FirstOrDefault();
                        model.RedBagBalance += item.Money;
                        dbContext.Update<Qxun.Activity.Contract.VIPPassRedBag013>(model);
                        item.Status = (int)TradeStatus.Fail;
                        item.Remark = "fail;time=" + DateTime.Now.ToString();
                        item.FinishTime = DateTime.Now;
                        dbContext.Update<VIPPassRedBag013Play>(item);
                        mode.RemainCount += ;
                        dbContext.Update<VIPPassRedBag013Mode>(mode);
                        trans.Complete();
                    }
                }
            }
        }
    }
    return View();
}

PS:经过这样改进，应该比之前的好多了。当然这样还是很远远不够的。希望各位路过的大神能够指点一二，甚是感谢！