Asp.net SharePoint 2013，自定义IHttpModule NullReferenceException

更新：问题已解决。继续阅读。

知道为什么添加自定义IHTTP模块显然不再可能了吗

我的问题涉及： 然而，这个问题很老，没有答案，也没有SharePoint上下文。我可以将我的HttpModule添加到任何标准ASP.NET WebForms页面

SharePoint正在IIS 8中托管。AppPool以集成模式运行。框架级别为4.0+

namespace My.Namespace
{
    using System;
    using System.Web;

    public class CustomHttpModule : IHttpModule
    {
        private static readonly object mutex = new object();
        private static bool _isInitialized;

        public void Init(HttpApplication context)
        {
            if (!_isInitialized)
            {
                lock (mutex)
                {
                    if (_isInitialized) return;

                    context.BeginRequest += BeginRequest;
                    _isInitialized = true;
                }
            }
        }

        private void BeginRequest(object sender, EventArgs e)
        {   
        }

        public void Dispose()
        {
        }
    }
}

结果：

<system.webServer>
<!-- further elements omitted -->
<modules runAllManagedModulesForAllRequests="true">
  <remove name="AnonymousIdentification" />
  <remove name="FileAuthorization" />
  <remove name="Profile" />
  <remove name="WebDAVModule" />
  <remove name="Session" />
  <add name="SPNativeRequestModule" preCondition="integratedMode" />
  <add name="SPRequestModule" preCondition="integratedMode" type="Microsoft.SharePoint.ApplicationRuntime.SPRequestModule, Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="ScriptModule" preCondition="integratedMode" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
  <add name="SharePoint14Module" preCondition="integratedMode" />
  <add name="StateServiceModule" type="Microsoft.Office.Server.Administration.StateModule, Microsoft.Office.Server, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="PublishingHttpModule" type="Microsoft.SharePoint.Publishing.PublishingHttpModule, Microsoft.SharePoint.Publishing, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="DesignHttpModule" preCondition="integratedMode" type="Microsoft.SharePoint.Publishing.Design.DesignHttpModule, Microsoft.SharePoint.Publishing, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="FederatedAuthentication" type="Microsoft.SharePoint.IdentityModel.SPFederationAuthenticationModule, Microsoft.SharePoint.IdentityModel, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="SessionAuthentication" type="Microsoft.SharePoint.IdentityModel.SPSessionAuthenticationModule, Microsoft.SharePoint.IdentityModel, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="SPWindowsClaimsAuthentication" type="Microsoft.SharePoint.IdentityModel.SPWindowsClaimsAuthenticationHttpModule, Microsoft.SharePoint.IdentityModel, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="SPApplicationAuthentication" type="Microsoft.SharePoint.IdentityModel.SPApplicationAuthenticationModule, Microsoft.SharePoint.IdentityModel, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="Session" type="System.Web.SessionState.SessionStateModule" />
  <add name="CustomModule" type="My.Namespace.CustomHttpModule, My.Namespace, Version=1.0.0.0, Culture=neutral, PublicKeyToken=066b2229567b6747" />
</modules>
<!-- further elements omitted -->
</system.webServer>

[NullReferenceException:对象引用未设置为对象的实例。] System.Web.PipelineModuleStepContainer.GetEventCount（RequestNotification通知，布尔值isPostEvent）+30
System.Web.PipelineStepManager.ResumeSteps（异常错误）+1098
System.Web.HttpApplication.BeginProcessRequestNotification（HttpContext上下文，异步回调cb）+135
System.Web.HttpRuntime.ProcessRequestNotificationPrivate（IIS7WorkerRequestWR，HttpContext上下文）+604

web.config如下所示：

<system.webServer>
<!-- further elements omitted -->
<modules runAllManagedModulesForAllRequests="true">
  <remove name="AnonymousIdentification" />
  <remove name="FileAuthorization" />
  <remove name="Profile" />
  <remove name="WebDAVModule" />
  <remove name="Session" />
  <add name="SPNativeRequestModule" preCondition="integratedMode" />
  <add name="SPRequestModule" preCondition="integratedMode" type="Microsoft.SharePoint.ApplicationRuntime.SPRequestModule, Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="ScriptModule" preCondition="integratedMode" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
  <add name="SharePoint14Module" preCondition="integratedMode" />
  <add name="StateServiceModule" type="Microsoft.Office.Server.Administration.StateModule, Microsoft.Office.Server, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="PublishingHttpModule" type="Microsoft.SharePoint.Publishing.PublishingHttpModule, Microsoft.SharePoint.Publishing, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="DesignHttpModule" preCondition="integratedMode" type="Microsoft.SharePoint.Publishing.Design.DesignHttpModule, Microsoft.SharePoint.Publishing, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="FederatedAuthentication" type="Microsoft.SharePoint.IdentityModel.SPFederationAuthenticationModule, Microsoft.SharePoint.IdentityModel, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="SessionAuthentication" type="Microsoft.SharePoint.IdentityModel.SPSessionAuthenticationModule, Microsoft.SharePoint.IdentityModel, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="SPWindowsClaimsAuthentication" type="Microsoft.SharePoint.IdentityModel.SPWindowsClaimsAuthenticationHttpModule, Microsoft.SharePoint.IdentityModel, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="SPApplicationAuthentication" type="Microsoft.SharePoint.IdentityModel.SPApplicationAuthenticationModule, Microsoft.SharePoint.IdentityModel, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
  <add name="Session" type="System.Web.SessionState.SessionStateModule" />
  <add name="CustomModule" type="My.Namespace.CustomHttpModule, My.Namespace, Version=1.0.0.0, Culture=neutral, PublicKeyToken=066b2229567b6747" />
</modules>
<!-- further elements omitted -->
</system.webServer>

一旦我不再附加BeginRequest事件，页面就会再次工作。但很明显，我的http模块已变得无用。

Edit 2013.09.19:Init（）在应用程序启动时被调用两次。如果我只在第二次调用时附加事件，应用程序会工作，但事件不会触发

编辑2013.09.20：问题大概已经解决。我的Init（）方法被触发了两次（其间没有调用Dispose（）），这一事实让我假设IHttpModule实际上可能有两个共存的实例。虽然我之前的观察表明，第二个实例可以附加事件（不触发，但也不会对应用程序产生负面影响），但事实显然并非如此，反之亦然（我的静态初始化“锁”就是这样）

---

**因此，IHttpModule的两个实例都需要具有相同的“配置”（附带eventhandlers）。运行多个HttpApplication实例是完全正常的。这是ASP.NET（或IIS）内部为优化目的所做的事情。这是要记住的关键：问题解决了。编辑的问题。请参见编辑2013.09.20