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 = 0; i < 50; 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(5);
//得到领取红包的金额
VIPPassRedBag013Mode currentMode = null;
foreach (var modeItem in mode)
{
if (modeItem.RemainCount > 0)
{
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 * 100);//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 = 199;
dbContext.Insert<VIPPassRedBag013Play>(currentPlayModel);
currentMode.RemainCount -= 1;
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(100);
if (time <= 1)
{
returnCode = "FAIL";
}
//模拟网络延迟
Thread.Sleep(time * 100);
//设置重新尝试次数
bool retry = true;
int retryCount = 0;
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 += 1;
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 > 5)
{
break;
}
} while (retry);
}
}

 

模拟100个人并发抢红包

public ActionResult Excute()
{
for (int i = 0; i < 100; 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 > 0)
{
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(100);
if (time <= 1)
{
returnCode = "FAIL";
}
//去查询微信红包的信息
//模拟网络延迟
Thread.Sleep(time * 100);
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 += 1;
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！