我们已经实现了一个对Active Directory进行身份验证的成员资格提供程序，它使用的是System.DirectoryServices。 在带有webdev服务器的Visual Studio 2010上的ASP.Net MVC 3应用程序中使用此成员资格提供程序时，我们有时（6次中有1次）在登录应用程序时会出现异常。
System.IO.FileNotFoundException: Could not load file or assembly 'System.Web' or one of its dependencies. The system cannot find the file specified.
File name: 'System.Web'
at System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
at System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
at System.Reflection.RuntimeAssembly.LoadWithPartialNameInternal(AssemblyName an, Evidence securityEvidence, StackCrawlMark& stackMark)
at System.DirectoryServices.AccountManagement.UnsafeNativeMethods.IADsPathname.Retrieve(Int32 lnFormatType)
at System.DirectoryServices.AccountManagement.ADStoreCtx.LoadDomainInfo()
at System.DirectoryServices.AccountManagement.ADStoreCtx.get_DnsDomainName()
at System.DirectoryServices.AccountManagement.ADStoreCtx.GetGroupsMemberOfAZ(Principal p)
at System.DirectoryServices.AccountManagement.UserPrincipal.GetAuthorizationGroupsHelper()
at System.DirectoryServices.AccountManagement.UserPrincipal.GetAuthorizationGroups()
=== Pre-bind state information ===
LOG: DisplayName = System.Web (Partial)
WRN: Partial binding information was supplied for an assembly:
WRN: Assembly Name: System.Web | Domain ID: 2
WRN: A partial bind occurs when only part of the assembly display name is provided.
WRN: This might result in the binder loading an incorrect assembly.
WRN: It is recommended to provide a fully specified textual identity for the assembly,
WRN: that consists of the simple name, version, culture, and public key token.
WRN: See whitepaper http://go.microsoft.com/fwlink/?LinkId=109270 for more information and common solutions to this issue.
Calling assembly : HibernatingRhinos.Profiler.Appender, Version=1.0.0.0, Culture=neutral, PublicKeyToken=0774796e73ebf640.
调用程序集是HibernatingRhinos.Profiler.Appender所以在log4net配置中禁用探查器后我们得到了真正的例外：
System.AppDomainUnloadedException: Attempted to access an unloaded appdomain. (Except at System.StubHelpers.StubHelpers.InternalGetCOMHRExceptionObject(Int32 hr, IntPtr pCPCMD, Object pThis)
at System.StubHelpers.StubHelpers.GetCOMHRExceptionObject(Int32 hr, IntPtr pCPCMD, Object pThis)
at System.DirectoryServices.AccountManagement.UnsafeNativeMethods.IADsPathname.Retrieve(Int32 lnFormatType)
at System.DirectoryServices.AccountManagement.ADStoreCtx.LoadDomainInfo()
at System.DirectoryServices.AccountManagement.ADStoreCtx.get_DnsDomainName()
at System.DirectoryServices.AccountManagement.ADStoreCtx.GetGroupsMemberOfAZ(Principal p)
at System.DirectoryServices.AccountManagement.UserPrincipal.GetAuthorizationGroupsHelper()
at System.DirectoryServices.AccountManagement.UserPrincipal.GetAuthorizationGroups()
异常总是以相同的方法抛出，但是现在我们无法随机重现它，但大约有6次中有1次。 但是，在使用II而不是内置的Visual Studio 2010 Web服务器时，我们不会遇到异常。
在Visual Studio webdev的上下文中使用多个appdomains时，它可能与比赛条件有关，但这只是猜测。 我们真的想知道问题的原因是什么，因为我们不希望在生产环境中出现这些异常。
我们发现了2个类似案例，但没有人找到真正的解决方案：
http://forums.asp.net/t/1556949.aspx/1
更新18-05-2011
重现异常的最小代码量（在asp.net mvc中），其中userName是您的Active Directory登录名。
using System.DirectoryServices.AccountManagement;
using System.Web.Mvc;
namespace ADBug.Controllers
{
public class HomeController : Controller
{
public ActionResult Index()
{
string userName = "nickvane";
var principalContext = new PrincipalContext(ContextType.Domain);
UserPrincipal userPrincipal = UserPrincipal.FindByIdentity(
principalContext,
IdentityType.SamAccountName,
userName);
if (userPrincipal != null)
{
PrincipalSearchResult<Principal> list = userPrincipal.GetAuthorizationGroups();
}
return View();
}
}
}
唉，异常仍然是随机发生的，所以没有完全可重现的bug。
答案 0 :(得分：83)
这对我有用（.Net 4）：
而不是：
principalContext = new PrincipalContext(ContextType.Domain)
使用域字符串创建主要上下文：
E.g。
principalContext = new PrincipalContext(ContextType.Domain,"MYDOMAIN")
它应该在4.5中修复。看到评论，尚未修复，但添加第二个参数仍然可以解决。
答案 1 :(得分：1)
我们在代码中通过重试对GetAuthorizationGroups的调用解决了它，但是介于两者之间。它解决了我们的问题，但我对此并不满意。
private PrincipalSearchResult<Principal> GetAuthorizationGroups(UserPrincipal userPrincipal, int tries)
{
try
{
return userPrincipal.GetAuthorizationGroups();
}
catch (AppDomainUnloadedException ex)
{
if (tries > 5)
{
throw;
}
tries += 1;
Thread.Sleep(1000);
return GetAuthorizationGroups(userPrincipal, tries);
}
}
如果我们得到异常，那么1次重试显然已经足够了。
答案 2 :(得分：1)
此解决方案非常慢，例如当您在Web应用程序中使用此解决方案时，GetAuthorizationGroups会经常被调用，这会使站点变得非常慢。我工作实现了som缓存，这在第一次之后变得更快。我也在重试，因为异常仍然存在。
首先，我重写GetRolesForUser方法并实现缓存。
public override string[] GetRolesForUser(string username)
{
// List of Windows groups for the given user.
string[] roles;
// Create a key for the requested user.
string cacheKey = username + ":" + ApplicationName;
// Get the cache for the current HTTP request.
Cache cache = HttpContext.Current.Cache;
// Attempt to fetch the list of roles from the cache.
roles = cache[cacheKey] as string[];
// If the list is not in the cache we will need to request it.
if (null == roles)
{
// Allow the base implementation to load the list of roles.
roles = GetRolesFromActiveDirectory(username);
// Add the resulting list to the cache.
cache.Insert(cacheKey, roles, null, Cache.NoAbsoluteExpiration,
Cache.NoSlidingExpiration);
}
// Return the resulting list of roles.
return roles;
}
GetRolesFromActiveDirectory看起来像这样。
public String[] GetRolesFromActiveDirectory(String username)
{
// If SQL Caching is enabled, try to pull a cached value.);));
if (_EnableSqlCache)
{
String CachedValue;
CachedValue = GetCacheItem('U', username);
if (CachedValue != "*NotCached")
{
return CachedValue.Split(',');
}
}
ArrayList results = new ArrayList();
using (PrincipalContext context = new PrincipalContext(ContextType.Domain, null, _DomainDN))
{
try
{
UserPrincipal p = UserPrincipal.FindByIdentity(context, IdentityType.SamAccountName, username);
var tries = 0;
var groups = GetAuthorizationGroups(p, tries);
foreach (GroupPrincipal group in groups)
{
if (!_GroupsToIgnore.Contains(group.SamAccountName))
{
if (_IsAdditiveGroupMode)
{
if (_GroupsToUse.Contains(group.SamAccountName))
{
results.Add(group.SamAccountName);
}
}
else
{
results.Add(group.SamAccountName);
}
}
}
}
catch (Exception ex)
{
throw new ProviderException("Unable to query Active Directory.", ex);
}
}
// If SQL Caching is enabled, send value to cache
if (_EnableSqlCache)
{
SetCacheItem('U', username, ArrayListToCSString(results));
}
return results.ToArray(typeof(String)) as String[];
}
最后一个方法是GetAuthorizationGroups，它看起来像这样。
private PrincipalSearchResult<Principal> GetAuthorizationGroups(UserPrincipal userPrincipal, int tries)
{
try
{
return userPrincipal.GetAuthorizationGroups();
}
catch(FileNotFoundException ex)
{
if (tries > 5) throw;
tries++;
Thread.Sleep(1000);
return GetAuthorizationGroups(userPrincipal, tries);
}
catch (AppDomainUnloadedException ex)
{
if (tries > 5) throw;
tries++;
Thread.Sleep(1000);
return GetAuthorizationGroups(userPrincipal, tries);
}
}
我发现缓存这些角色会让它变得更快。希望这有助于某人。 欢呼声。
答案 3 :(得分：1)
使用ActiveDirectoryMembershipProvider时遇到了同样的问题。对我来说，当我第一次调用Membership.ValidateUser（）并且框架试图创建提供者时，就发生了这种情况。
我注意到我的临时开发计算机没有安装Visual Studio 2010 SP1，所以我安装了它，这解决了我的问题。
答案 4 :(得分：1)
我遇到了同样的问题，我在this帖子中找到了答案。似乎是PrincipalContext构造函数的问题，它只将ContextType作为参数。我知道这篇文章很老了，但我想以后会把它链接给任何人：）
答案 5 :(得分：-1)
转到项目属性/ Web选项卡/服务器部分，然后选中NTML身份验证复选框。
这是Cassini（VS Development Server）使用Windows身份验证所必需的。