WCF Duplex：在 ASP.NET 4.0 Webforms 客户端中接收回调的 FatalException答案

【问题标题】：WCF Duplex: FatalException receiving callback in ASP.NET 4.0 Webforms clientWCF Duplex：在 ASP.NET 4.0 Webforms 客户端中接收回调的 FatalException
【发布时间】：2015-10-07 16:12:54
【问题描述】：

我在使用双工服务和使用该服务的 asp.net 4.0 webforms 应用程序时遇到了一个非常奇怪的问题。

在我的开发机器中，代码工作正常，没有错误，但是在我的应用程序测试服务器中测试相同的代码我得到 System.Runtime.FatalException 消息：对象引用未设置为对象的实例当我向客户端发送回调时。

我的开发机器是：Windows 8.1，IIS 8.5。

测试服务器是 Azure 上的虚拟机：Windows Server 2008 Datacenter、IIS 7.5

服务和客户端应用程序都是：.NET Framework 4.0

考虑到一个非常奇怪的事情是我尝试远程调试 VM 上的应用程序并启用远程调试后服务行为正常，但是一旦取消附加调试器，错误再次出现。

所以，代码是：

服务

[ServiceContract(CallbackContract = typeof(IProcessCallback))]
public interface IProcess
{
    [OperationContract(IsOneWay = true)]
    void Process(ProcessRequest request);
}

public interface IProcessCallback
{
    [OperationContract(IsOneWay = true)]
    void NotifyOk(string id, string message);

    [OperationContract(IsOneWay = true)]
    void NotifyError(string id, string message);
}

服务实现

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall, ConcurrencyMode = ConcurrencyMode.Reentrant)]
public class Processor : IProcess
{
    public void Process(ProcessRequest request)
    {
        try
        {
            //Some logic here...

            var callbackChannel = GetCallback();
            callbackChannel.NotifyOk(id, msg);
        }
        catch (Exception ex)
        {
            //Some error handling logic here...

            var callbackChannel = GetCallback();
            callbackChannel.NotifyError(id, msg);
        }
    }

    private static IProcessCallback GetCallback()
    {
        return OperationContext.Current.GetCallbackChannel<IProcessCallback>();
    }
}

在 asp.net 客户端项目中，我使用向导添加了对服务的引用。

使用服务的 aspx 页面背后的代码：

[CallbackBehavior(ConcurrencyMode = ConcurrencyMode.Reentrant, UseSynchronizationContext = false, AutomaticSessionShutdown = false)]
public partial class LoadPage : System.Web.UI.Page, IProcessCallback
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void btnProcess_OnClick(object sender, EventArgs e)
    {
        try
        {
            var instanceContext = new InstanceContext(this);
            var proxyDuplex = new ProcessorClient(instanceContext);

            proxyDuplex.Process(new ProcessRequest());
        }
        catch (Exception ex)
        {
            //Some exception handling code here...
        }
    }

    public void NotifyOk(string id, string msg)
    {
        //Some logic...
    }

    public void NotifyError(string id, string msg)
    {
        //Some logic...
    }
}

如果启用了远程调试，此代码在开发机器和测试服务器上也能正常工作。

我在 web.config（WCF 项目和 ASP.NET 项目）中启用了 WCF 跟踪，并使用“SvcTraceViewer.exe”工具检查日志文件我发现 ASP.NET 项目在尝试时出现错误处理回调：

来自标记为异常的活动的 XML 信息（在 .svclog 文件上）

<E2ETraceEvent xmlns="http://schemas.microsoft.com/2004/06/E2ETraceEvent">
<System xmlns="http://schemas.microsoft.com/2004/06/windows/eventlog/system">
<EventID>131075</EventID>
<Type>3</Type>
<SubType Name="Error">0</SubType>
<Level>2</Level>
<TimeCreated SystemTime="2015-07-16T16:51:44.9708260Z" />
<Source Name="System.ServiceModel" />
<Correlation ActivityID="{06c345d5-3374-4692-98c6-0256c236f70d}" />
<Execution ProcessName="w3wp" ProcessID="4432" ThreadID="39" />
<Channel />
<Computer>SERVERWS2008R2</Computer>
</System>
<ApplicationData>
<TraceData>
<DataItem>
<TraceRecord xmlns="http://schemas.microsoft.com/2004/10/E2ETraceEvent/TraceRecord" Severity="Error">
<TraceIdentifier>http://msdn.microsoft.com/en-US/library/System.ServiceModel.Diagnostics.ThrowingException.aspx</TraceIdentifier>
<Description>Throwing an exception.</Description>
<AppDomain>/LM/W3SVC/1/ROOT/MyApplication.Web-1-130815389967873315</AppDomain>
<Exception>
<ExceptionType>System.Runtime.FatalException, System.Runtime.DurableInstancing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35</ExceptionType>
<Message>Object reference not set to an instance of an object.</Message>
<StackTrace>
at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage4(MessageRpc&amp; rpc)
at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage31(MessageRpc&amp; rpc)
at System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet)
at System.ServiceModel.Dispatcher.ChannelHandler.DispatchAndReleasePump(RequestContext request, Boolean cleanThread, OperationContext currentOperationContext)
at System.ServiceModel.Dispatcher.ChannelHandler.HandleRequest(RequestContext request, OperationContext currentOperationContext)
at System.ServiceModel.Dispatcher.ChannelHandler.AsyncMessagePump(IAsyncResult result)
at System.Runtime.Fx.AsyncThunk.UnhandledExceptionFrame(IAsyncResult result)
at System.ServiceModel.Diagnostics.TraceUtility.&lt;&gt;c__DisplayClass4.&lt;CallbackGenerator&gt;b__2(AsyncCallback callback, IAsyncResult result)
at System.Runtime.AsyncResult.Complete(Boolean completedSynchronously)
at System.Runtime.InputQueue`1.AsyncQueueReader.Set(Item item)
at System.Runtime.InputQueue`1.Dispatch()
at System.ServiceModel.Channels.ReliableDuplexSessionChannel.ProcessDuplexMessage(WsrmMessageInfo info)
at System.ServiceModel.Channels.ReliableDuplexSessionChannel.HandleReceiveComplete(IAsyncResult result)
at System.ServiceModel.Channels.ReliableDuplexSessionChannel.OnReceiveCompletedStatic(IAsyncResult result)
at System.Runtime.Fx.AsyncThunk.UnhandledExceptionFrame(IAsyncResult result)
at System.Runtime.AsyncResult.Complete(Boolean completedSynchronously)
at System.ServiceModel.Channels.ReliableChannelBinder`1.InputAsyncResult`1.OnInputComplete(IAsyncResult result)
at System.Runtime.Fx.AsyncThunk.UnhandledExceptionFrame(IAsyncResult result)
at System.ServiceModel.Diagnostics.TraceUtility.&lt;&gt;c__DisplayClass4.&lt;CallbackGenerator&gt;b__2(AsyncCallback callback, IAsyncResult result)
at System.Runtime.AsyncResult.Complete(Boolean completedSynchronously)
at System.Runtime.InputQueue`1.AsyncQueueReader.Set(Item item)
at System.Runtime.InputQueue`1.Dispatch()
at System.Runtime.ActionItem.DefaultActionItem.Invoke()
at System.Runtime.ActionItem.CallbackHelper.InvokeWithoutContext(Object state)
at System.Runtime.IOThreadScheduler.ScheduledOverlapped.IOCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped)
at System.Runtime.Fx.IOCompletionThunk.UnhandledExceptionFrame(UInt32 error, UInt32 bytesRead, NativeOverlapped* nativeOverlapped)
at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP)
</StackTrace>
<ExceptionString>System.Runtime.FatalException: Object reference not set to an instance of an object. ---&gt; System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Web.HttpApplication.ThreadContext.Enter(Boolean setImpersonationContext)
   at System.Web.HttpApplication.OnThreadEnterPrivate(Boolean setImpersonationContext)
   at System.Web.AspNetSynchronizationContext.CallCallbackPossiblyUnderLock(SendOrPostCallback callback, Object state)
   at System.Web.AspNetSynchronizationContext.CallCallback(SendOrPostCallback callback, Object state)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage4(MessageRpc&amp; rpc)
   --- End of inner exception stack trace ---</ExceptionString>
<InnerException>
<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.HttpApplication.ThreadContext.Enter(Boolean setImpersonationContext)
at System.Web.HttpApplication.OnThreadEnterPrivate(Boolean setImpersonationContext)
at System.Web.AspNetSynchronizationContext.CallCallbackPossiblyUnderLock(SendOrPostCallback callback, Object state)
at System.Web.AspNetSynchronizationContext.CallCallback(SendOrPostCallback callback, Object state)
at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage4(MessageRpc&amp; rpc)
</StackTrace>
<ExceptionString>System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Web.HttpApplication.ThreadContext.Enter(Boolean setImpersonationContext)
   at System.Web.HttpApplication.OnThreadEnterPrivate(Boolean setImpersonationContext)
   at System.Web.AspNetSynchronizationContext.CallCallbackPossiblyUnderLock(SendOrPostCallback callback, Object state)
   at System.Web.AspNetSynchronizationContext.CallCallback(SendOrPostCallback callback, Object state)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage4(MessageRpc&amp; rpc)</ExceptionString>
</InnerException>
</Exception>
</TraceRecord>
</DataItem>
</TraceData>
</ApplicationData>

感谢您的帮助

【问题讨论】：

NullReferenceException 的几乎所有情况都是相同的。请参阅“What is a NullReferenceException in .NET?”获取一些提示。

标签： c# asp.net wcf webforms wcf-binding

【解决方案1】：

如果将来有人遇到同样的问题，这就是解决方案。

我的代码中的错误是我正在创建这样的 InstanceContext：

var instanceContext = new InstanceContext(this);
var proxyDuplex = new ProcessorClient(instanceContext);

对于 InstanceContext 构造函数，需要将初始化上下文的类的实例作为参数传递，在我的例子中是 aspx 页面，所以我使用了页面的类名 (LoadPage.aspx) ：

var instanceContext = new InstanceContext(new LoadPage());
var proxyDuplex = new ProcessorClient(instanceContext);

就是这样！

【讨论】：