asp.net - 经过一段时间的工作后，IIS/ASP.Net 无法从 WCF Web 服务的 web.config 文件中读取设置

Question

我们有一个在 IIS7 上运行的 ASP.Net Web 应用程序，与 WCF Web 服务进行通信，该服务处理从此 Web 应用程序到达的请求。

工作一段时间后(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，并记录了以下异常:

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:\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...
}

对自定义设置实例的访问现在在顶级父类Request中实现，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;
    }

    // ....
}

<小时/>

不仅此特定设置 ValidateIpConnections 会出现此问题，WCF 服务的 web.config 文件中的其他设置也会出现此问题。

目前还不清楚这个问题的原因是什么，它不能持续稳定地重现。它似乎并不直接取决于负载/用户数量/打开的 session 。有时，该网站可以顺利运行数周，然后该问题每周出现一次，然后连续出现几天。可能与应用池中某些worker进程的回收有关。

我们以前在 Windows Server 2003 (IIS 6.0) 上遇到它，现在在带有 IIS 7.0 的 Windows Server 2008 上遇到它，因此它似乎与 IIS 版本没有直接关系。

我怀疑通过 Request 的只读静态成员为所有仅初始化一次的子类共享对 CustomSettings 类实例的访问可能存在问题。

任何帮助/建议将不胜感激。

Answer 1

我认为您可以避免使用自定义设置类，因为 web.config 在第一次访问时会被缓存。参见

ASP.NET: Where/how is web.config cached?

因此无需自己进行缓存，然后就可以排除这种情况。

我们的一台生产服务器上也遇到了类似的问题，结果发现病毒扫描程序正在扫描 web.config 文件，从而导致应用程序池回收。

我会推荐

• 去掉静态类，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
• 发生异常时查看事件日志，看看是否还有其他奇怪的事情发生
• 设置 asp.net 监控(ASP.NET 计数器 > 应用程序重新启动):http://msdn.microsoft.com/en-us/library/ms972959.aspx和 http://blogs.msdn.com/b/johan/archive/2008/02/18/monitoring-application-pool-and-application-restarts.aspx