经过一段时间的工作,IIS / ASP.Net无法从WCF Web服务的web.confi

经过一段时间的工作(可能是一周或几天),WCF Web服务开始无法读取其web.config文件中的设置,记录了以下异常：

System.NullReferenceException

ABC.Communication.DataContract.RefreshRequest System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Xml.XmlNode.RemoveChild(XmlNode oldChild)
   at System.Xml.XmlNode.RemoveAll()
   at System.Xml.XmlElement.set_InnerXml(String value)
   at System.Configuration.LocalFileSettingsProvider.XmlEscaper.Unescape(String escapedString)
   at System.Configuration.LocalFileSettingsProvider.GetPropertyValues(SettingsContext context,SettingsPropertyCollection properties)
   at System.Configuration.SettingsBase.GetPropertiesFromProvider(SettingsProvider provider)
   at System.Configuration.SettingsBase.GetPropertyValueByName(String propertyName)
   at System.Configuration.SettingsBase.get_Item(String propertyName)
   at System.Configuration.ApplicationSettingsBase.GetPropertyValue(String propertyName)
   at System.Configuration.ApplicationSettingsBase.get_Item(String propertyName)
   at ABC.Communication.DataContract.Request.ValidateIpAddress() in C:ProjectABC.ServerABC.CommunicationDataContractRequest.Validation.cs:line 955
   at ABC.Communication.DataContract.RefreshRequestBase.Validate() in C:ProjectABC.ServerABC.CommunicationDataContractRefreshRequestBase.cs:line 46
   at ABC.Communication.DataContract.RefreshRequest.Validate() in C:ProjectABC.ServerABC.CommunicationDataContractRefreshRequest.cs:line 30
   at ABC.Communication.ClientCommunicationService.HandleRequest(Request request) in C:ProjectABC.ServerABC.CommunicationClientCommunicationService.cs:line 116

或System.ArgumentException

ABC.Communication.DataContract.RefreshRequest System.ArgumentException: The node to be removed is not a child of this node.
   at System.Xml.XmlNode.RemoveChild(XmlNode oldChild)
   at System.Xml.XmlNode.RemoveAll()
   at System.Xml.XmlElement.set_InnerXml(String value)
   at System.Configuration.LocalFileSettingsProvider.XmlEscaper.Unescape(String escapedString)
   at System.Configuration.LocalFileSettingsProvider.GetPropertyValues(SettingsContext context,SettingsPropertyCollection properties)
   at System.Configuration.SettingsBase.GetPropertiesFromProvider(SettingsProvider provider)
   at System.Configuration.SettingsBase.GetPropertyValueByName(String propertyName)
   at System.Configuration.SettingsBase.get_Item(String propertyName)
   at System.Configuration.ApplicationSettingsBase.GetPropertyValue(String propertyName)
   at System.Configuration.ApplicationSettingsBase.get_Item(String propertyName)
   at ABC.Communication.DataContract.Request.ValidateIpAddress() in C:ProjectABC.ServerABC.CommunicationDataContractRequest.Validation.cs:line 955
   at ABC.Communication.DataContract.RefreshRequestBase.Validate() in C:ProjectABC.ServerABC.CommunicationDataContractRefreshRequestBase.cs:line 46
   at ABC.Communication.DataContract.DataContracts.RefreshRequest.Validate() in C:ProjectABC.ServerABC.CommunicationDataContractRefreshRequest.cs:line 30
   at ABC.Communication.ClientCommunicationService.HandleRequest(Request request) in C:ProjectABC.ServerABC.CommunicationClientCommunicationService.cs:line 116

或System.Configuration.SettingsPropertyNotFoundException：

ABC.Communication.DataContract.RefreshRequest System.Configuration.SettingsPropertyNotFoundException: The settings property 'ValidateIpConnections' was not found.
   at System.Configuration.SettingsBase.GetPropertyValueByName(String propertyName)
   at System.Configuration.SettingsBase.get_Item(String propertyName)
   at System.Configuration.ApplicationSettingsBase.GetPropertyValue(String propertyName)
   at System.Configuration.ApplicationSettingsBase.get_Item(String propertyName)
   at ABC.Communication.DataContract.Request.ValidateIpAddress() in C:ProjectABC.ServerABC.CommunicationDataContractRequest.Validation.cs:line 955
   at ABC.Communication.DataContract.RefreshRequestBase.Validate() in C:ProjectABC.ServerABC.CommunicationDataContractRefreshRequestBase.cs:line 46
   at ABC.Communication.DataContract.RefreshRequest.Validate() in C:ProjectABC.ServerABC.CommunicationDataContractRefreshRequest.cs:line 30
   at ABC.Communication.ClientCommunicationService.HandleRequest(Request request) in C:ProjectABC.ServerABC.CommunicationClientCommunicationService.cs:line 116

抛出此异常的代码非常简单：

private void ValidateIpAddress() {
    // Load custom settings
    CustomSettings settings = GetCustomSettings();

    if (!settings.ValidateIpConnections)   // here the exception is thrown!
        return;

    // the rest of code never reached...
}

现在,在顶级父类Request中实现对自定义设置实例的访问,如下所示：

public abstract partial class Request
{
    /// <summary>
    /// Custom settings.
    /// </summary>
    private static readonly CustomSettings customSettings;

    /// <summary>
    /// .cctor().
    /// </summary>
    static Request()
    {
        customSettings = new CustomSettings();
    }

    /// <summary>
    /// Get custom settings.
    /// </summary>
    /// <returns>Custom settings.</returns>
    internal static CustomSettings GetCustomSettings()
    {
        return customSettings;
    }

    // ....
}

问题不仅发生在此特定设置ValidateIpConnections,还发生在WCF服务的web.config文件中的其他设置.

目前尚不清楚这种问题的原因是什么,它不能经常和稳定地再现.它似乎并不直接取决于负载/用户数/开放会话数.有时网站运行平稳数周,然后问题每周发生一次,然后连续几天发生.可能,它与应用程序池中的某些工作进程的回收有关.

我们曾经在Windows Server 2003(IIS 6.0)上遇到过它,现在可以在带有IIS 7.0的Windows Server 2008上使用它,因此它似乎与IIS的版本没有直接关系.

我怀疑通过只有初始化一次的所有子类的Request的readonly静态成员共享对CustomSettings类实例的访问可能存在问题.

任何帮助/建议将不胜感激.