.NET 异步核心中的 Rebus 崩溃答案

【问题标题】：Rebus crash in .NET async core.NET 异步核心中的 Rebus 崩溃
【发布时间】：2016-11-02 12:47:33
【问题描述】：

我正在尝试将现有网站从 Rebus 0.45 升级到 Rebus 2.0，但遇到了 System.Web.ThreadContext.AssociateWithCurrentThread 因空引用而崩溃的问题。我完全不知道为什么，所以我正在寻找我可以寻找的可能原因。

我拥有的唯一跟踪是 Windows 事件日志，它在尝试发送消息时注册以下内容：

An unhandled exception occurred and the process was terminated.

Application ID: /LM/W3SVC/1/ROOT/website

Process ID: 14460

Exception: System.NullReferenceException

Message: Object reference not set to an instance of an object.

StackTrace:    at System.Web.ThreadContext.AssociateWithCurrentThread(Boolean setImpersonationContext)
   at System.Web.HttpApplication.OnThreadEnterPrivate(Boolean setImpersonationContext)
   at System.Web.LegacyAspNetSynchronizationContext.CallCallbackPossiblyUnderLock(SendOrPostCallback callback, Object state)
   at System.Web.LegacyAspNetSynchronizationContext.CallCallback(SendOrPostCallback callback, Object state)
   at System.Web.LegacyAspNetSynchronizationContext.Post(SendOrPostCallback callback, Object state)
   at System.Threading.Tasks.SynchronizationContextAwaitTaskContinuation.PostAction(Object state)
   at System.Threading.Tasks.AwaitTaskContinuation.RunCallback(ContextCallback callback, Object state, Task& currentTask)
--- End of stack trace from previous location where exception was thrown ---
   at System.Threading.Tasks.AwaitTaskContinuation.<>c.<ThrowAsyncIfNecessary>b__18_0(Object s)
   at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
   at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()

该网站正在运行带有 Castle Windsor 依赖注入器的 ASP.NET MVC 3.0，并使用 Rebus.SqlServer 作为单向客户端进行传输设置：

var busConfigurer = Configure.With(new CastleWindsorContainerAdapter(container))
  .Logging(l => l.Use(new RebusLoggerFactory()))
  .Routing(t => t.TypeBased().AddEndpointMappingsFromAppConfig())
  .Subscriptions(s => s.StoreInSqlServer(dbConnectionString, "RebusSubscriptions_v2"))
  .Transport(t => t.UseSqlServerAsOneWayClient(dbConnectionString, "RebusMessages_v2"))
  Start();

为“.NET 4.5”应用程序池设置了 IIS。

网站启动和总线日志：

- Supplied connection string will be modified to enable MARS
- Database already contains a table named 'RebusMessages_v2' - will not create anything
- Supplied connection string will be modified to enable MARS
- Starting periodic task 'CleanupTrackedErrors' with interval 00:01:00
- Starting bus 1
- Started

稍后会通过 Rebus 发送一条消息，记录：

- Sending SubmissionCreatedEvent -> SelfService.Service.input

...然后轰隆隆！整个应用程序崩溃。

在发送消息之前，应用程序已与 NHibernate 交互以存储有关操作的详细信息。

更新

通过将Bus.Send(msg) 更改为Bus.Send(msg).Start()，我可以在Visual Studio 中进行调试时同步触发相同的错误并获得以下堆栈跟踪：

Exception thrown: 'System.NullReferenceException' in System.Web.dll
Exception thrown: 'System.NullReferenceException' in mscorlib.dll
System.Transactions Critical: 0 : 
<TraceRecord xmlns="http://schemas.microsoft.com/2004/10/E2ETraceEvent/TraceRecord" Severity="Critical"><TraceIdentifier>http://msdn.microsoft.com/TraceCodes/System/ActivityTracing/2004/07/Reliability/Exception/Unhandled</TraceIdentifier><Description>Unhandled exception</Description><AppDomain>/LM/W3SVC/1/ROOT/website-2-131225642632547395</AppDomain>
<Exception><ExceptionType>System.NullReferenceException, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</ExceptionType><Message>Object reference not set to an instance of an object.</Message><StackTrace>   at System.Web.ThreadContext.AssociateWithCurrentThread(Boolean setImpersonationContext)
   at System.Web.HttpApplication.OnThreadEnterPrivate(Boolean setImpersonationContext)
   at System.Web.LegacyAspNetSynchronizationContext.CallCallbackPossiblyUnderLock(SendOrPostCallback callback, Object state)
   at System.Web.LegacyAspNetSynchronizationContext.CallCallback(SendOrPostCallback callback, Object state)
   at System.Web.LegacyAspNetSynchronizationContext.Post(SendOrPostCallback callback, Object state)
   at System.Threading.Tasks.SynchronizationContextAwaitTaskContinuation.PostAction(Object state)
   at System.Threading.Tasks.AwaitTaskContinuation.RunCallback(ContextCallback callback, Object state, Task&amp;amp; currentTask)
--- End of stack trace from previous location where exception was thrown ---
   at System.Threading.Tasks.AwaitTaskContinuation.&amp;lt;&amp;gt;c.&amp;lt;ThrowAsyncIfNecessary&amp;gt;b__18_0(Object s)
   at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
   at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()</StackTrace><ExceptionString>System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Web.ThreadContext.AssociateWithCurrentThread(Boolean setImpersonationContext)
   at System.Web.HttpApplication.OnThreadEnterPrivate(Boolean setImpersonationContext)
   at System.Web.LegacyAspNetSynchronizationContext.CallCallbackPossiblyUnderLock(SendOrPostCallback callback, Object state)
   at System.Web.LegacyAspNetSynchronizationContext.CallCallback(SendOrPostCallback callback, Object state)
   at System.Web.LegacyAspNetSynchronizationContext.Post(SendOrPostCallback callback, Object state)
   at System.Threading.Tasks.SynchronizationContextAwaitTaskContinuation.PostAction(Object state)
   at System.Threading.Tasks.AwaitTaskContinuation.RunCallback(ContextCallback callback, Object state, Task&amp;amp; currentTask)
--- End of stack trace from previous location where exception was thrown ---
   at System.Threading.Tasks.AwaitTaskContinuation.&amp;lt;&amp;gt;c.&amp;lt;ThrowAsyncIfNecessary&amp;gt;b__18_0(Object s)
   at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
   at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()</ExceptionString></Exception></TraceRecord>

更新二

用bus.Advanced.Routing.Send("SelfService.Service.input", msg) 替换Bus.Publish(msg) 有效。所以显然订阅/路由的东西有问题，因为Send(...) 绕过了那个。

更新 III

显然在 web.config 中添加<httpRuntime targetFramework="4.6" ... 解决了这个问题（到目前为止，它似乎仍然有点不稳定）。 web.config 已经有<compilation ... targetFramework="4.6">:

  <system.web>
    <httpRuntime targetFramework="4.6" maxRequestLength="5000" requestValidationMode="2.0" />
    <compilation debug="true" targetFramework="4.6">
      <assemblies>...</assemblies>
    </compilation>
    <pages validateRequest="false">
      <namespaces>...</namespaces>
    </pages>
  </system.web>

【问题讨论】：

当我在谷歌上搜索“nullreferenceexception onthreadenterprivate”时，我找到了this other SO post，这表明当您忘记await 时会发生异常......到await Bus.Send(yourMessage)?
没有“await”，因为它给了我“'await' 运算符只能在异步方法中使用。”并且现有代码都不是异步的。所有这些异步的东西对我来说都是新的，所以任何帮助都表示赞赏:-)
另见更新 III
似乎 ASP.NET 从同步调用异步存在一些问题。参见例如stackoverflow.com/questions/12701879/…
关于更新 II：当您显式发送到一个特定队列时，它会绕过路由器查找（这是异步的），这意味着如果 async/await 导致问题，它的行为可能会有所不同。

标签： asp.net-mvc rebus

【解决方案1】：

解决办法是确保网站运行的是 .NET 4.5 或更高版本：

<system.web>
  <httpRuntime targetFramework="4.6" />
  <compilation targetFramework="4.6">
    ...
  </compilation>
</system.web>

显然 ASP.NET 团队在 .NET 4.5 中让 ASP.NET 对任务更加敏感。

【讨论】：