WCF的DataContractSerilaizer线程安全吗？
我一直在将一个相当大的系统从Remoting转换为WCF，并且一切似乎运行良好，除了我们经常遇到以下exception：“System.InvalidOperationException：Collection被修改;枚举操作可能无法执行。” 我没有任何运气跟踪它，因为它只发生在有数百个调用通过时，我只能假设它是因为一个对象被修改，因为它被序列化。
所有类都使用： [DataContract(IsReference=true)] 。
使用远程处理时没有类似的例外，所以我想知道是否有人在WCF中遇到过类似的问题或者可以让我知道它可能是序列化程序 – 在这种情况下我假设我必须编写自己的序列化程序来执行在必要时locks （这是我宁愿避免的一项重大任务）。
以下是堆栈跟踪：
WCF Error: at System.Collections.Generic.List1.Enumerator.MoveNextRare() at WriteArrayOfLineToXml(XmlWriterDelegator , Object , XmlObjectSerializerWriteContext , CollectionDataContract ) at System.Runtime.Serialization.CollectionDataContract.WriteXmlValue(XmlWriterDelegator xmlWriter, Object obj, XmlObjectSerializerWriteContext context) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.InternalSerialize(XmlWriterDelegator xmlWriter, Object obj, Boolean isDeclaredType, Boolean writeXsiType, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.InternalSerializeReference(XmlWriterDelegator xmlWriter, Object obj, Boolean isDeclaredType, Boolean writeXsiType, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle) at WriteLineGroupToXml(XmlWriterDelegator , Object , XmlObjectSerializerWriteContext , ClassDataContract ) at System.Runtime.Serialization.ClassDataContract.WriteXmlValue(XmlWriterDelegator xmlWriter, Object obj, XmlObjectSerializerWriteContext context) 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 System.Runtime.Serialization.XmlObjectSerializerWriteContext.InternalSerializeReference(XmlWriterDelegator xmlWriter, Object obj, Boolean isDeclaredType, Boolean writeXsiType, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle) at WriteLineToXml(XmlWriterDelegator , Object , XmlObjectSerializerWriteContext , ClassDataContract ) at System.Runtime.Serialization.ClassDataContract.WriteXmlValue(XmlWriterDelegator xmlWriter, Object obj, XmlObjectSerializerWriteContext context) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeAndVerifyType(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, Boolean verifyKnownType, RuntimeTypeHandle declaredTypeHandle, Type declaredType) at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeWithXsiTypeAtTopLevel(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle originalDeclaredTypeHandle, Type graphType) at System.Runtime.Serialization.DataContractSerializer.InternalWriteObjectContent(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver) at System.Runtime.Serialization.DataContractSerializer.InternalWriteObject(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver) at System.Runtime.Serialization.XmlObjectSerializer.WriteObjectHandleExceptions(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver) at System.Runtime.Serialization.XmlObjectSerializer.WriteObject(XmlDictionaryWriter writer, Object graph) at System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter.SerializeParameterPart(XmlDictionaryWriter writer, PartInfo part, Object graph) at System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter.SerializeParameter(XmlDictionaryWriter writer, PartInfo part, Object graph) at System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter.SerializeBody(XmlDictionaryWriter writer, MessageVersion version, String action, MessageDescription messageDescription, Object returnValue, Object[] parameters, Boolean isRequest) at System.ServiceModel.Dispatcher.OperationFormatter.SerializeBodyContents(XmlDictionaryWriter writer, MessageVersion version, Object[] parameters, Object returnValue, Boolean isRequest) at System.ServiceModel.Dispatcher.OperationFormatter.OperationFormatterMessage.OperationFormatterBodyWriter.OnWriteBodyContents(XmlDictionaryWriter writer) at System.ServiceModel.Channels.BodyWriter.WriteBodyContents(XmlDictionaryWriter writer) at System.ServiceModel.Channels.BodyWriterMessage.OnWriteBodyContents(XmlDictionaryWriter writer) at System.ServiceModel.Channels.Message.OnWriteMessage(XmlDictionaryWriter writer) at System.ServiceModel.Channels.Message.WriteMessage(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.FramingDuplexSessionChannel.EncodeMessage(Message message) at System.ServiceModel.Channels.FramingDuplexSessionChannel.OnSend(Message message, TimeSpan timeout) at System.ServiceModel.Channels.OutputChannel.Send(Message message, TimeSpan timeout) at System.ServiceModel.Dispatcher.DuplexChannelBinder.DuplexRequestContext.OnReply(Message message, TimeSpan timeout) at System.ServiceModel.Channels.RequestContextBase.Reply(Message message, TimeSpan timeout) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.Reply(MessageRpc& rpc)
实际上，使用DataContractSerializer可以轻松地重现此错误。 它不涉及DataContractSerializer线程安全性，它是关于某些集合的线程安全性，用于您的数据协定：
[DataContract] public class C { [DataMember] public List Values { get; set; } } class Program { static void Main(string[] args) { var c = new C { Values = new List () }; var serializer = new DataContractSerializer(typeof(C)); Task .Factory .StartNew(() => { while (true) { Console.WriteLine("Trying to add new item."); c.Values.Add(DateTime.Now.Millisecond); } }, TaskCreationOptions.LongRunning); Task .Factory .StartNew(() => { while (true) { using (var stream = new MemoryStream()) { Console.WriteLine("Trying to serialize."); serializer.WriteObject(stream, c); } } }, TaskCreationOptions.LongRunning); Console.ReadLine(); }
在短暂的执行时间之后，您将获得具有类似堆栈跟踪的IOE：
at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource) at System.Collections.Generic.List`1.Enumerator.MoveNextRare() at System.Collections.Generic.List`1.Enumerator.MoveNext() at WriteArrayOfintToXml(XmlWriterDelegator , Object , XmlObjectSerializerWriteContext , CollectionDataContract ) at System.Runtime.Serialization.CollectionDataContract.WriteXmlValue(XmlWriterDelegator xmlWriter, Object obj, XmlObjectSerializerWriteContext context)
看起来你正在继续修改一些同时序列化的共享数据。 您可以打开WCF跟踪（请参阅此问题）以找出导致此错误的操作，并仔细查看此操作使用的数据。
然后，根据当前服务行为的InstanceContextMode和ConcurrencyMode属性的值，您可以选择要走的路：
- 要么使用一些锁定;
- 或使用任何线程安全的集合;
- 或改变服务行为;
- 或改变服务本身（例如，使其无国籍）。
如果丹尼斯的假设是正确的，那么解决这个问题的最简单方法是复制集合并通过网络发送副本。 此时，在序列化期间是否修改了原始内容并不重要