從WCF客戶端內部調試NullReference異常

Question

我們有一個WCF服務，大致是以下客戶端代碼：

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();
}

它似乎工作正常，但在我們的beta環境中，一旦在~70000次調用中拋出NullReferenceException。 我們仔細記錄異常和所有數據，看起來它不依賴於任何方式的數據。 如果我在異常后立即重復呼叫（只需一段時間直到成功），它會順利進行。

異常顯得非常罕見，我無法重現，跟蹤或調試它。 在調用時似乎立即拋出異常，不調用任何服務器代碼。

這是堆棧跟蹤：

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() 

關於在哪里搜索答案的任何想法？

Answer 1

聽起來這可能是一個線程問題 - 也許WCF客戶端代碼重復使用相同的序列化程序實例進行多次調用，而且它正在破壞它們。

你能嘗試將你的調用發送到一個lock塊中的client.MyWcfMethod()嗎？

例如：

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

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