ASP.NET HttpContext缓存在插入后立即删除

我有一个ASP.NET 4 web服务
它在ModuleController控制器中具有ImportModule动作。

这就是它的工作原理：

1. 用户将模块上传为CSV文件
2. 正在使用HttpPostedFileBase.InputStream和自定义CSV读取类读取此文件
3. 根据一些规则和验证，该文件正在转换为C#对象。如果一个文件是有效的，那么它将转换为C#对象，存储在具有唯一GUID名称的缓存中，并且用户将重定向到CompleteImportModule操作
4. 用户检查数据是否正确，并确认上传

长话短说，有一个代码告诉你更多：
ImportModule动作。

public ActionResult ImportModule(HttpPostedFileBase file)
{
    if (!ModelState.IsValid) 
    {
        return RedirectToAction("Index");
    }
    ModuleQuestion[] questions;
    ModuleInfo moduleInfo;
    string uploadId = Guid.NewGuid().ToString();
    // It is my custom CSV-reader and it works. Values are assigned
    FormDataCsvReader csvReader = new FormDataCsvReader(file.InputStream);
    if (!csvReader.Process(out questions, out moduleInfo))
    {
        // File is invalid
        return RedirectToAction("Index");
    }
    ViewBag.UploadId = uploadId;
    ViewBag.ModuleInfo = moduleInfo;
    ViewBag.Questions = questions;
    HttpContext.Cache.Add("UploadModule_" + uploadId,
        new Tuple<ModuleInfo, ModuleQuestion[]>(moduleInfo, questions),
        null,
        Cache.NoAbsoluteExpiration,
        TimeSpan.FromMinutes(30),
        CacheItemPriority.NotRemovable,
        (k, v, r) => 
        {
            LoggingFactory.GetLogger().Debug("Removed from cache: {0}. Reason: {1}", k, r);
        });     
    return View();   
}

视图ImportModule:

// Output data from ViewBag.ModuleInfo and ViewBag.Questions
<form method="POST" action="@Url.Action("CompleteImportModule")">
    <input type="hidden" name="uploadId" value="@ViewBag.UploadId"/>
    <input type="submit" value="Send">
</form>

CompleteImportModule动作：

[HttpPost]
public ActionResult CompleteImportModule(string uploadId)
{
    var item = HttpContext.Cache["UploadModule_" + uploadId];
    if (item == null) RedirectToAction("Index");
    // upload module 
    HttpContext.Cache.Remove("UploadModule_" + uploadId);
    return RedirectToAction("Index");
}

然而，我遇到了一些问题。我无法上传模块，因为该值在插入后立即从缓存中删除。它只存储一秒钟：

DEBUG 2015-06-22 15:00:18,696 thread 85: Added to cache:
UploadModule_c843077d-21d0-4e9f-9e5e-3df82da4bac8
DEBUG 2015-06-22 15:00:19,935 thread 48: Removed from cache:
UploadModule_c843077d-21d0-4e9f-9e5e-3df82da4bac8. Reason: Removed

reason是"已删除"的，这意味着它没有过期，IIS也没有因为优化而删除它，但看起来我删除的是我自己。我非常确信，在CompleteImportModule之前，我甚至不会访问这个缓存记录。

我试着把new StackTrace().ToString()放在CacheItemRemovedCallback中。就是这样，如果它能以某种方式提供帮助的话：

at CPMAdministrator.Controllers.ModulesReferenceController.<ImportModule>b__9(String key, Object value, CacheItemRemovedReason reason)
   at System.Web.Caching.CacheEntry.CallCacheItemRemovedCallback(CacheItemRemovedCallback callback, CacheItemRemovedReason reason)
   at System.Web.Caching.CacheEntry.Close(CacheItemRemovedReason reason)
   at System.Web.Caching.CacheSingle.UpdateCache(CacheKey cacheKey, CacheEntry newEntry, Boolean replace, CacheItemRemovedReason removedReason, Object& valueOld)
   at System.Web.Caching.CacheSingle.Dispose(Boolean disposing)
   at System.Web.Caching.CacheMultiple.Dispose(Boolean disposing)
   at System.Web.HttpRuntime.Dispose()
   at System.Web.HttpRuntime.ReleaseResourcesAndUnloadAppDomain(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()

为什么会这样？这有点像IIS池回收吗？如何确保文件不会被删除？或者，我如何以另一种方式有效地存储这些数据？

at System.Web.HttpRuntime.Dispose()
at System.Web.HttpRuntime.ReleaseResourcesAndUnloadAppDomain(Object state)

public class MvcApplication : HttpApplication
{
    protected void Application_End()
    {
    }
}