带有 WaitHandle 的 HttpHandler 中的 NullReferenceException答案

【问题标题】：NullReferenceException in HttpHandler with WaitHandle带有 WaitHandle 的 HttpHandler 中的 NullReferenceException
【发布时间】：2020-06-05 19:49:21
【问题描述】：

我有一个带有长轮询 IHttpAsyncHandler 的旧版 Web 表单应用程序，它开始在事件日志中引发异常，但信息很少。如果长轮询 XMLHttpRequest 未决并且我对 web.config 进行了更改，我可以在 IIS express 中重现该错误。这会回收进程并在调试器和事件日志中引发相同的 NullReferenceException：

Event code: 3005 
Event message: An unhandled exception has occurred. 
Event time: 05/06/2020 2:30:09 PM 
Event time (UTC): 05/06/2020 6:30:09 PM 
Event ID: c8428fb2935c47be90ebc6a7849063e6 
Event sequence: 7 
Event occurrence: 1 
Event detail code: 0 

Application information: 
    Application domain: /LM/W3SVC/2/ROOT/WebApp-2-132358551451863719 
    Trust level: Full 
    Application Virtual Path: /WebApp 
    Application Path: C:\Users\naask\source\repos\WebApp\ 
    Machine name: DESKTOP-S7T1J31 

Process information: 
    Process ID: 11892 
    Process name: iisexpress.exe 
    Account name: DESKTOP-S7T1J31\naask 

Exception information: 
    Exception type: NullReferenceException 
    Exception message: Object reference not set to an instance of an object.
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step)
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)



Request information: 
    Request URL: http://localhost:48061/WebApp/edits?id=~/somepath.aspx/26264&wait=true 
    Request path: /WebApp/edits 
    User host address: ::1 
    User:  
    Is authenticated: False 
    Authentication Type:  
    Thread account name: DESKTOP-S7T1J31\naask 

Thread information: 
    Thread ID: 6 
    Thread account name: DESKTOP-S7T1J31\naask 
    Is impersonating: False 
    Stack trace:    at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step)
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)


Custom event details:

在调试器中，尝试加载符号信息，但失败：

异常信息与事件日志数据匹配：

System.NullReferenceException: Object reference not set to an instance of an object.
  at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()

大概我正在寻找的符号在 System.Web 中，但我已经加载了这些符号并且我已经 setup VS to debug framework code:

我不确定从这里去哪里调试 IHttpAsyncHandler 的问题。长轮询处理程序使用信号量上的ThreadPool.RegisterWaitForSingleObject 来等待事件，并在该事件发生时同时释放所有等待者。我只在 AppPool 回收后看到这些错误。

【问题讨论】：

标签： asp.net webforms

【解决方案1】：

我从来没有找到解决缺失源问题的方法来调试它，但经过一些详尽的案例缩减后，问题的根源是通过 IHttpAsyncHandler 的路径，其中返回的 IAsyncResult 为空。

【讨论】：