关于.net:记一次-NET-某药品仓储管理系统-卡死分析

一：背景

1. 讲故事

这个月初，有位敌人wx上找到我，说他的api过一段时间后，就会呈现只有申请，没有响应的状况，截图如下：

从敌人的形容中看样子程序是被什么货色卡住了，这种卡死的问题解决起来绝对简略，接下来我就用 windbg 给大家剖析一下。

二：Windbg 剖析

1. Request 申请正在干嘛？

既然敌人说 api 有 request 无 response，那怎么去验证敌人的话对不对呢？咱们都晓得 .NET 用 HttpContext 来示意一个申请，话中有话就是能够去抓 HttpContext 下的时长属性，Netext 中有一个 !whttp 命令能够帮忙咱们。

0:000> !whttpHttpContext    Thread Time Out Running  Status Verb     Url000000563bf803b0   42 00:01:50 00:01:24    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=x-HN000000563bf84660   -- 00:01:50 Finished    200 GET      http://xxx.com:30003/000000563c4a0470   51 00:01:50 00:00:12    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=xxx2C00000056bbf63590   30 00:01:50 00:02:41    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=xxx-B2C00000056bc82a038   -- 00:01:50 Finished    200 GET      http://localhost:30003/00000056bc84a3e8   44 00:01:50 00:00:51    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=x00000056bc8671c8   46 00:01:50 00:00:45    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=xxx-B2C000000573bf44698   35 00:01:50 00:02:39    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=x000000573bf483c0   33 00:01:50 00:02:41    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=x-HN000000573bf97e80   40 00:01:50 00:02:32    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=ZJB2C000000573c583b08   -- 00:01:50 Finished    200 GET      http://localhost:30003/000000573c589ec8   -- 00:01:50 Finished    200 GET      http://xxx.com:30003/Wms/xxx/xxx/xxx000000573c760e28   -- 00:01:50 Finished    200 POST     http://xxx.com:30003/Wms/xxx/xxx/xxx000000573c95f990   48 00:01:50 00:00:31    200 POST     http://xxx.com:30003/Wms/Common/xxx?xxx=xxx&xxx=x-HN00000057bbf4f8e8   31 00:01:50 00:02:12    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=x00000057bc080340   50 00:01:50 00:00:19    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=x000000583c4aee80   43 00:01:50 00:01:11    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=xxx2B000000583c4d0c50   53 00:01:50 00:00:01    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=xxx2B00000058bbf8f1a0   34 00:01:50 00:02:22    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=xxx2B000000593bfe1758   41 00:01:50 00:01:22    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=xxx2C000000593c892160   -- 00:01:50 Finished    200 GET      http://xxx.com:30003/Wms/xxx/xxx/xxxJob000000593ca813b0   45 00:01:50 00:00:30    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=xxx-HN000000593caa45d8   -- 00:01:50 Finished    200 GET      http://xxx.com:30003/00000059bc1ad808   32 00:01:50 00:01:45    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=xxx-B2C00000059bc1c3d70   36 00:01:50 00:01:29    200 POST     http://xxx.com:30003/Wms/xxx/xxx?xxx=xxx&xxx=x25 HttpContext object(s) found matching criteria

从 Running 列能够看到大多申请都曾经达到1分钟以上，这也验证了敌人所说的卡死问题，依照教训，能够取 Running 列中最大的 httpContext 所在的线程，也就是下面的 30 和 33 号线程，看看它们都在干什么？

2. 探索 Running 最长线程

接下来切到 30 和 33 号线程，看看它们的线程栈。

0:000> ~30sntdll!NtWaitForSingleObject+0xa:00007ffd`b81f024a c3              ret0:030> !clrstack OS Thread Id: 0x29d0 (30)        Child SP               IP Call Site0000005acc3ac590 00007ffdb81f024a [PrestubMethodFrame: 0000005acc3ac590] xxx.xxx.RedisConnectionHelp.get_Instance()0000005acc3ac850 00007ffd4dd78911 xxx.xxx.RedisCache..ctor(Int32, System.String)0000005acc3ac8c0 00007ffd4dd78038 xxx.xxx.CacheByRedis.HashGet[[System.__Canon, mscorlib]](System.String, System.String, Int32)0000005acc3ac968 00007ffdabef1f7c [StubHelperFrame: 0000005acc3ac968] 0000005acc3ac9c0 00007ffd4dd77f18 xxx.xxx.Cache.xxx.GetCacheNotAreaDataEntity[[System.__Canon, mscorlib]](System.String, System.String, System.String)...0:030> ~33sntdll!NtWaitForMultipleObjects+0xa:00007ffd`b81f07ba c3              ret0:033> !clrstack OS Thread Id: 0x3ad4 (33)        Child SP               IP Call Site0000005accabae90 00007ffdb81f07ba [GCFrame: 0000005accabae90] 0000005accabafb8 00007ffdb81f07ba [HelperMethodFrame_1OBJ: 0000005accabafb8] System.Threading.Monitor.ObjWait(Boolean, Int32, System.Object)0000005accabb0d0 00007ffdaac60d64 System.Threading.ManualResetEventSlim.Wait(Int32, System.Threading.CancellationToken)0000005accabb160 00007ffdaac5b4bb System.Threading.Tasks.Task.SpinThenBlockingWait(Int32, System.Threading.CancellationToken)0000005accabb1d0 00007ffdab5a01d1 System.Threading.Tasks.Task.InternalWait(Int32, System.Threading.CancellationToken)0000005accabb2a0 00007ffdab59cfa7 System.Threading.Tasks.Task`1[[System.__Canon, mscorlib]].GetResultxxx(Boolean)0000005accabb2e0 00007ffd4d8d338f xxx.Config.xxx.Config`1[[System.__Canon, mscorlib]].GetConfig(xxx.Config.Model.ConfigListener, System.Func`2<xxx.Config.Request.GetConfigRequest,System.Threading.Tasks.Task`1<System.String>>)0000005accabb340 00007ffd4d8d2f40 xxx.Config.xxx.Config`1[[System.__Canon, mscorlib]].get_Item(System.String, System.String)0000005accabb3c0 00007ffd4dd78f7f xxx.Util.BaseConfig.get_GetRedisConn()0000005accabb440 00007ffd4dd78e9c xxx.xxx.RedisConnectionHelp.GetConnectionString()0000005accabb4a0 00007ffd4dd789cb xxx.xxx.RedisConnectionHelp..cctor()0000005accabb940 00007ffdabef6953 [GCFrame: 0000005accabb940] 0000005accabc5b0 00007ffdabef6953 [PrestubMethodFrame: 0000005accabc5b0] xxx.xxx.RedisConnectionHelp.get_Instance()0000005accabc870 00007ffd4dd78911 xxx.xxx.RedisCache..ctor(Int32, System.String)0000005accabc8e0 00007ffd4dd78038 xxx.xxx.CacheByRedis.HashGet[[System.__Canon, mscorlib]](System.String, System.String, Int32)0000005accabc988 00007ffdabef1f7c [StubHelperFrame: 0000005accabc988] 0000005accabc9e0 00007ffd4dd77f18 xxx.Core.Cache.xxx.GetCacheNotAreaDataEntity[[System.__Canon, mscorlib]](System.String, System.String, System.String)...

下面的信息不难发现 30 号线程正卡在 RedisConnectionHelp.get_Instance() 处，33 号线曾经进入了 RedisConnectionHelp.get_Instance() 办法中，最初在 GetConfig() 处期待 Result 的后果，按教训来说，30 号线程看样子正在锁期待， 33 号正在期待异步后果，接下来的突破点就是探索下 RedisConnectionHelp.Instance 处代码。

3. 寻找问题代码

接下来用反编译工具 ILSpy 找到问题代码。

public static class RedisConnectionHelp{    public static ConnectionMultiplexer Instance    {        get        {            if (_instance == null)            {                lock (Locker)                {                    if (_instance == null || !_instance.IsConnected)                    {                        _instance = GetManager();                    }                }            }            return _instance;        }    }}

30 号线程果然是卡在 Locker 处，接下来深挖下 33 号线程所执行的 GetManager() 办法，简化后代码如下：

public T this[string dataId, string key = ""]{    get    {        try        {            string config = GetConfig(configListener, new NacosConfigClient(Base.NacosConfiguration).DoGetConfigAsync);            return JsonConvert.DeserializeObject<T>(config);        }        catch (Exception ex)        {            return default(T);        }    }}private string GetConfig(ConfigListener listener, Func<GetConfigRequest, Task<string>> action){    var text2 = action(new GetConfigRequest    {        DataId = listener.DataId,        Group = listener.Group,        Tenant = text    }).Result;    return text2;}internal async Task<string> DoGetConfigAsync(GetConfigRequest request){    IRestResponse restResponse = await HttpUtil.Request(currentServerAddr, Method.GET, request.ParamValues(), xxx);    return restResponse.Content;}

能够看到代码卡在了 Result 上无限期期待，到这里我就想到了 同步上下文 ，我看他这个程序是 .NET 4.8 下的 ASP.NET MVC，记得不错上下文应该是 AspNetSynchronizationContext，具体死锁起因可参见我的这篇文章：一句 Task.Result 就死锁, 这代码还怎么写？，解决办法大略有四种。

应用 .ConfigureAwait(false)
改成全异步
用 Task 再包一层。
改成全同步

三：总结

其实本次事变次要还是因为在 同步代码 中做了 异步代码.Result 导致的死锁问题，有十分多的文章都在鞭挞这种景象，在 asp.net core 中曾经移除了这种同步上下文的大坑，给到敌人的倡议是改成全同步，死锁问题也随之隐没。

哈哈，真替敌人开心！