问题描述
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我们在IIS7上运行一个ASP.Net Web应用程序,该应用程序与WCF Web服务进行通信,该服务处理从该Web应用程序收到的请求。
工作一段时间后(可能是一周或几天),WCF Web服务开始记录其以下异常,从而无法读取其web.config文件中的设置:
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:\\Project\\ABC.Server\\ABC.Communication\\DataContract\\Request.Validation.cs:line 955
at ABC.Communication.DataContract.RefreshRequestBase.Validate() in C:\\Project\\ABC.Server\\ABC.Communication\\DataContract\\RefreshRequestBase.cs:line 46
at ABC.Communication.DataContract.RefreshRequest.Validate() in C:\\Project\\ABC.Server\\ABC.Communication\\DataContract\\RefreshRequest.cs:line 30
at ABC.Communication.ClientCommunicationService.HandleRequest(Request request) in C:\\Project\\ABC.Server\\ABC.Communication\\ClientCommunicationService.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:\\Project\\ABC.Server\\ABC.Communication\\DataContract\\Request.Validation.cs:line 955
at ABC.Communication.DataContract.RefreshRequestBase.Validate() in C:\\Project\\ABC.Server\\ABC.Communication\\DataContract\\RefreshRequestBase.cs:line 46
at ABC.Communication.DataContract.DataContracts.RefreshRequest.Validate() in C:\\Project\\ABC.Server\\ABC.Communication\\DataContract\\RefreshRequest.cs:line 30
at ABC.Communication.ClientCommunicationService.HandleRequest(Request request) in C:\\Project\\ABC.Server\\ABC.Communication\\ClientCommunicationService.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:\\Project\\ABC.Server\\ABC.Communication\\DataContract\\Request.Validation.cs:line 955
at ABC.Communication.DataContract.RefreshRequestBase.Validate() in C:\\Project\\ABC.Server\\ABC.Communication\\DataContract\\RefreshRequestBase.cs:line 46
at ABC.Communication.DataContract.RefreshRequest.Validate() in C:\\Project\\ABC.Server\\ABC.Communication\\DataContract\\RefreshRequest.cs:line 30
at ABC.Communication.ClientCommunicationService.HandleRequest(Request request) in C:\\Project\\ABC.Server\\ABC.Communication\\ClientCommunicationService.cs:line 116
引发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中实现了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;
}
// ....
}
不仅对于此特定设置ValidateIpConnections,而且对于WCF服务的web.config文件中的其他设置,都会出现此问题。
根本不清楚造成这种问题的原因是什么,它不能持续稳定地再现。它似乎并不直接取决于负载/用户数量/打开的会话。有时,该站点可以正常运行数周,然后该问题每周发生一次,然后连续几天发生。可能与应用程序池中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,现在在带有IIS 7.0的Windows Server 2008上得到了它,因此它似乎与IIS版本没有直接关系。
我怀疑通过对所有子类仅初始化一次的Request的只读静态成员共享对CustomSettings类实例的访问权限可能会出现问题。
任何帮助/建议将不胜感激。
解决方法
我认为您可以避免使用自定义设置类,因为web.config会在首次访问时被缓存。看到
ASP.NET:web.config的缓存位置/方式?
因此,您无需进行自己的缓存,然后就可以排除该缓存。
我们在其中一台生产服务器上遇到了类似的问题,结果发现病毒扫描程序正在扫描web.config文件,这导致应用程序池回收。
我会推荐
删除静态类并直接使用.net配置类
调整病毒扫描程序,使其不扫描应用程序所在的文件夹
在发生异常时查看事件日志,以查看是否还有其他奇怪的事情发生
设置asp.net监视(ASP.NET计数器>应用程序重新启动):http://msdn.microsoft.com/zh-cn/library/ms972959.aspx和http://blogs.msdn.com/b/johan/存档/2008/02/18/monitoring-application-pool-and-application-restarts.aspx