c# - MemoryCache 在域未处理异常后始终返回 null

Question

我的 MemoryCache (System.Runtime.Caching) 存在问题。对于有关此对象的其他问题，我发现在域未处理的异常之后没有缓存任何值。

异常(exception)是:

Exception: System.TypeInitializationException 
Message: The type initializer for 'System.Web.Util.ExecutionContextUtil' threw an exception. 
Trace: 
at System.Web.Util.ExecutionContextUtil.RunInNullExecutionContext(Action callback) 
at System.Web.Hosting.ObjectCacheHost.System.Runtime.Caching.Hosting.IMemoryCacheManager.UpdateCacheSize(Int64 size, MemoryCache memoryCache) 
at System.Runtime.Caching.CacheMemoryMonitor.GetCurrentPressure() 
at System.Runtime.Caching.MemoryMonitor.Update() 
at System.Runtime.Caching.MemoryCacheStatistics.CacheManagerThread(Int32 minPercent) 
at System.Threading.ExecutionContext.runTryCode(Object userData) 
at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) 
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx) 
at System.Threading._TimerCallback.PerformTimerCallback(Object state)

Caused by Exception: System.Exception Message: Type 'System.Threading.ExecutionContext' does not have a public property named 'PreAllocatedDefault'. 
Trace: at System.Web.Util.ExecutionContextUtil.GetDummyDefaultEC() 
at System.Web.Util.ExecutionContextUtil..cctor() 

异常似乎在 2 到 5 分钟后抛出。我认为解决这个异常应该可以解决我的问题，因为缓存不会被释放。

这个问题是从昨天 19 点开始的，即使我已经使用了 3 个月了......12天以来，生产没有发生任何变化。服务器托管在 Azure 上(操作系统是 Windows Server 2008 R2)

编辑异常处理程序

public class Global : System.Web.HttpApplication
{
    void Application_Start(object sender, EventArgs e) {
        System.Threading.Thread.GetDomain().UnhandledException += new UnhandledExceptionEventHandler(Global_UnhandledException);
        System.Threading.Thread.GetDomain().DomainUnload += new EventHandler(Global_DomainUnload);
    }
}

内存缓存包装器

    public abstract class MemoryCacheManager : ICacheManager
{

    private MemoryCache MemoryCache;

    protected MemoryCacheManager()
    {
        MemoryCache = new MemoryCache("Common.Utils.MemoryCacheManager");
    }

    private void ItemRemoved(CacheEntryRemovedArguments arguments)
    {
        switch (arguments.RemovedReason)
        {
            case CacheEntryRemovedReason.CacheSpecificEviction:
                LogManager.Instance.Log(arguments.CacheItem.Key + " : CacheSpecificEviction");
                break;
            case CacheEntryRemovedReason.ChangeMonitorChanged:
                LogManager.Instance.Log(arguments.CacheItem.Key + " : ChangeMonitorChanged");
                break;
            case CacheEntryRemovedReason.Evicted:
                LogManager.Instance.Log(arguments.CacheItem.Key + " : Evicted");
                break;
            case CacheEntryRemovedReason.Expired:
                LogManager.Instance.Log(arguments.CacheItem.Key + " : Expired");
                break;
            case CacheEntryRemovedReason.Removed:
                LogManager.Instance.Log(arguments.CacheItem.Key + " : Removed");
                break;
        }

    }

    #region ICacheManager        
    public void Add(string key, object value, DateTimeOffset absoluteExpiration)
    {
        var policy = new CacheItemPolicy { AbsoluteExpiration = absoluteExpiration, RemovedCallback = ItemRemoved };
        Add(key, value, policy);
    }

    public void Add(string key, object value, TimeSpan slidingExpiration)
    {
        var policy = new CacheItemPolicy { SlidingExpiration = slidingExpiration, RemovedCallback = ItemRemoved };
        Add(key, value, policy);
    }

    private void Add(string key, object value, CacheItemPolicy policy)
    {
        MemoryCache.Add(key, value, policy);
        LogManager.Instance.Info(DateTime.Now.ToString("MM/dd/yyyy hh:mm:ss") + " " + key + " : Added");
    }

    public object Get(string key)
    {
        return MemoryCache.Get(key);
    }

    public bool Exist(string key)
    {
        return MemoryCache.Contains(key);
    }

    public bool Remove(string key)
    {
        return MemoryCache.Remove(key) != null;
    }
    #endregion
}

缓存管理器

    public class CacheManager : MemoryCacheManager
{

    #region Singleton
    private static readonly CacheManager instance = new CacheManager();

    // Explicit static constructor to tell C# compiler ot to mark type as beforefieldinit
    static CacheManager() { }

    private CacheManager() 
        : base()
    {
    }

    public static CacheManager Instance
    {
        get
        {
            return instance;
        }
    }
    #endregion
}

第一次调用Global_UnhandledException后，所有CacheManager.Instance.Get都返回null。

我的问题是:如何避免这种异常？或者如何让memorycache正常工作

Answer 1

我也遇到过这个异常，我能够使用 HTTP 模块将其输出到文本文件以捕获未处理的异常，这往往发生在页面请求/响应执行之外。

message=The type initializer for 'System.Web.Util.ExecutionContextUtil' threw an exception.
stack= at System.Web.Util.ExecutionContextUtil.RunInNullExecutionContext(Action callback)
at System.Web.Hosting.ObjectCacheHost.System.Runtime.Caching.Hosting.IMemoryCacheManager.UpdateCacheSize(Int64 size, MemoryCache memoryCache)
at System.Runtime.Caching.CacheMemoryMonitor.GetCurrentPressure()
at System.Runtime.Caching.MemoryMonitor.Update()
at System.Runtime.Caching.MemoryCacheStatistics.CacheManagerThread(Int32 minPercent)
at System.Runtime.Caching.MemoryCacheStatistics.CacheManagerTimerCallback(Object state)
at System.Threading._TimerCallback.TimerCallback_Context(Object state)
at System.Threading.ExecutionContext.runTryCode(Object userData)
at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
at System.Threading._TimerCallback.PerformTimerCallback(Object state)

type=System.Exception

message=Type 'System.Threading.ExecutionContext' does not have a public property named 'PreAllocatedDefault'.

stack=at System.Web.Util.ExecutionContextUtil.GetDummyDefaultEC()
at System.Web.Util.ExecutionContextUtil..cctor()

编辑:值得注意的是，抛出此异常后，缓存完全停止工作。

我在研究这个问题时遇到了这个:

http://blogs.msdn.com/b/kwill/archive/2013/09/11/august-2013-windows-azure-guest-os-issue-with-system-runtime-caching-memorycache.aspx

在文中他们说:“此操作系统版本包含标准安全补丁，包括 https://support.microsoft.com/kb/2862772 (MS13-059) 中的修复程序，这是 Internet Explorer 的累积安全更新。此 IE 补丁引入了回归，导致在 ASP.NET 应用程序中使用 System.Runtime.Caching.MemoryCache 时出现上述异常。”

随后，他们给出了三种解决方案，第一种是回滚到应用修补程序之前。第二个告诉你避免使用 MemoryCache(很好)。唯一的其他解决方案就是等待他们修复此问题并在 10 月初(2013 年)暗示。

“下一个 Windows Azure guest 操作系统版本将包含 IE 修补程序来解决此问题，并应在 10 月初开始推广到 Azure。”

此页面的呈现方式听起来好像这个问题只是 Windows Azure 的问题。但我认为它会影响任何具有此修补程序并运行 ASP.NET 应用程序的平台。虽然 Windows 7(这是我的操作系统)的“关键”更新，但针对 Windows Server 2008 推出的修补程序似乎被标记为“中等”。这可能会有所帮助，因为虽然它会影响我的开发平台，但不会影响我的生产服务器。我在下面的安全公告中找到了此信息:

http://technet.microsoft.com/en-us/security/bulletin/ms13-059

有趣的是，当我必须在 ASP.NET 应用程序中添加使用 OutputCache 进行子操作的解决方案时，我不再遇到此问题，尽管我仍然继承自 MemoryCache。

如果有用的话，我将包含我使用过的代码，并且我相信以下博客为我节省了大量时间:

http://www.haneycodes.net/custom-output-caching-with-mvc3-and-net-4-0-done-right/

下面的代码...

public class CustomMemoryCache : MemoryCache
    {
    public CustomMemoryCache(string name)
        : base(name)
        {
        }

    public override bool Add(string key, object value, DateTimeOffset absoluteExpiration, string regionName = null)
        {
        System.Web.Caching.OutputCache.Providers[System.Web.Caching.OutputCache.DefaultProviderName].Add(key, value, absoluteExpiration.DateTime);
        return true;
        }

    public override object Get(string key, string regionName = null)
        {
        return System.Web.Caching.OutputCache.Providers[System.Web.Caching.OutputCache.DefaultProviderName].Get(key);
        }
    }

在我的 Global.asax.cs 中:

protected void Application_Start()
    {
        OutputCacheAttribute.ChildActionCache = new CustomMemoryCache("MyCache");
    }

还有一个提供者:

public class MyCacheItem
    {
    public Object ItemData { get; set; }
    public DateTime UtcExpiry { get; set; }
    public DateTime UtcAdded { get; set; }
    }

public class MyOutputCacheProvider: OutputCacheProvider
    {
    private readonly Dictionary<String, MyCacheItem> CacheDictionary = new Dictionary<String, MyCacheItem>(); 

    public override object Get(string key)
        {
        lock(CacheDictionary)
            {
            if (!CacheDictionary.ContainsKey(key))
                return null;

            var Item = CacheDictionary[key];

            // Item has expired?
            if (Item.UtcExpiry < DateTime.UtcNow)
                {
                Remove(key);
                return null;
                }

            return Item.ItemData;
            }
        }

    public override object Add(string key, object entry, DateTime utcExpiry)
        {
        lock (CacheDictionary)
            {
            if (!CacheDictionary.ContainsKey(key))
                {
                MyCacheItem CacheItem = new MyCacheItem
                    {
                        ItemData = entry, 
                        UtcExpiry = utcExpiry,
                        UtcAdded =  DateTime.UtcNow
                    };

                CacheDictionary.Add(key, CacheItem);
                return CacheItem.ItemData;
                }

            var Item = CacheDictionary[key];
            return Item.ItemData;
            }
        }

    public override void Set(string key, object entry, DateTime utcExpiry)
        {
        lock (CacheDictionary)
            {
            if (!CacheDictionary.ContainsKey(key))
                {
                Add(key, entry, utcExpiry);
                return;
                }

            CacheDictionary[key].ItemData = entry;
            CacheDictionary[key].UtcExpiry = utcExpiry;
            }
        }

    public override void Remove(string key)
        {
        lock (CacheDictionary)
            {
            if (!CacheDictionary.ContainsKey(key))
                return;

            CacheDictionary.Remove(key);
            }
        }
    }

最后，web.config:

<system.web>        
    <caching>
        <outputCache defaultProvider="MyCache">
            <providers>
                <add name="MyCache" type="MyApp.Namespace.MyOutputCacheProvider"/>
            </providers>
        </outputCache>
    </caching>
</system.web>