調試NullReference例外內部構件

Question

我們有一個WCF服務，大致有以下客戶端代碼：

bool success = false; 
IClientChannel proxy = null; 
try 
{ 
    var client = channelFactory.CreateChannel(new EndpointAddress(url)); 
    proxy = client as IClientChannel; 
    proxy.Open(); 
    client.MyWcfMethod(a, b, c);         
    proxy.Close(); 
    success = true; 
} 
finally 
{ 
    if (!success) 
    proxy.Abort(); 
} 

這似乎很好地工作，但在我們的測試環境下，一旦〜70000呼叫引發NullReferenceException 。我們仔細記錄異常和所有數據，看起來它不以任何方式依賴於數據。如果我在異常之後立即重複該呼叫（只是一段時間，直到成功），它會順利進行。

這個異常顯得非常罕見，我無法複製，追蹤或調試它。異常似乎在調用時立即拋出，沒有調用服務器代碼。

這裏是堆棧跟蹤：

Object reference not set to an instance of an object. Server stack trace: 
at System.Xml.Linq.ElementWriter.WriteElement(XElement e) 
at System.Xml.Linq.XElement.WriteTo(XmlWriter writer) 
at System.Xml.Linq.XElement.System.Xml.Serialization.IXmlSerializable.WriteXml(XmlWriter writer) 
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.WriteIXmlSerializable(XmlWriterDelegator xmlWriter, Object obj, XmlSerializableWriter xmlSerializableWriter) 
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.WriteIXmlSerializable(XmlWriterDelegator xmlWriter, Object obj) 
at System.Runtime.Serialization.XmlDataContract.WriteXmlValue(XmlWriterDelegator xmlWriter, Object obj, XmlObjectSerializerWriteContext context) 
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.WriteDataContractValue(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle declaredTypeHandle) 
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeWithoutXsiType(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle declaredTypeHandle) 
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.InternalSerialize(XmlWriterDelegator xmlWriter, Object obj, Boolean isDeclaredType, Boolean writeXsiType, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle) 
at WriteCallContextToXml(XmlWriterDelegator , Object , XmlObjectSerializerWriteContext , ClassDataContract) 
at System.Runtime.Serialization.ClassDataContract.WriteXmlValue(XmlWriterDelegator xmlWriter, Object obj, XmlObjectSerializerWriteContext context) 
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.WriteDataContractValue(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle declaredTypeHandle) 
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeWithoutXsiType(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle declaredTypeHandle) 
at System.Runtime.Serialization.DataContractSerializer.InternalWriteObjectContent(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver) 
at System.Runtime.Serialization.DataContractSerializer.InternalWriteObjectContent(XmlWriterDelegator writer, Object graph) 
at System.Runtime.Serialization.XmlObjectSerializer.WriteObjectContentHandleExceptions(XmlWriterDelegator writer, Object graph) 
at System.Runtime.Serialization.DataContractSerializer.WriteObjectContent(XmlDictionaryWriter writer, Object graph) 
at System.ServiceModel.Channels.XmlObjectSerializerHeader.OnWriteHeaderContents(XmlDictionaryWriter writer, MessageVersion messageVersion) 
at System.ServiceModel.Channels.MessageHeader.WriteHeaderContents(XmlDictionaryWriter writer, MessageVersion messageVersion) 
at System.ServiceModel.Channels.MessageHeaders.WriteHeaderContents(Int32 headerIndex, XmlDictionaryWriter writer) 
at System.ServiceModel.Channels.Message.WriteMessagePreamble(XmlDictionaryWriter writer) at System.ServiceModel.Channels.Message.OnWriteMessage(XmlDictionaryWriter writer) at System.ServiceModel.Channels.BufferedMessageWriter.WriteMessage(Message message, BufferManager bufferManager, Int32 initialOffset, Int32 maxSizeQuota) 
at System.ServiceModel.Channels.BinaryMessageEncoderFactory.BinaryMessageEncoder.WriteMessage(Message message, Int32 maxMessageSize, BufferManager bufferManager, Int32 messageOffset) 
at System.ServiceModel.Channels.HttpOutput.SerializeBufferedMessage(Message message) 
at System.ServiceModel.Channels.HttpOutput.Send(TimeSpan timeout) 
at System.ServiceModel.Channels.HttpChannelFactory`1.HttpRequestChannel.HttpChannelRequest.SendRequest(Message message, TimeSpan timeout) 
at System.ServiceModel.Channels.RequestChannel.Request(Message message, TimeSpan timeout) at System.ServiceModel.Dispatcher.RequestChannelBinder.Request(Message message, TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout) 
at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation) 
at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message) Exception rethrown at [0]: at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg) 
at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type) 
at IMyService.MyWcfMethod(int a, string b, double c) 
at MyClientClass.Process() 

在何處尋找答案任何想法？

Answer 1

聽起來這可能是一個線程問題 - 也許WCF客戶端代碼重複使用相同的序列化器實例進行多次調用，並且這是破壞性的東西。

你可以嘗試在lock區塊內撥打電話client.MyWcfMethod()嗎？

例如爲：

private static readonly object _wcfSync = new object(); 
... 

    lock (_wcfSync) 
    { 
    client.MyWcfMethod(a, b, c); 
    }