是什么导致我的httpcontext.缓存将被删除在我的c# MVC web应用程序

本文关键字：我的 MVC 删除 web 应用程序 httpcontext 缓存是什么 | 更新日期: 2023-09-27 18:14:15

我们有一个web应用程序，它从SOAP web服务检索大量数据，并且需要大约4到5分钟来完成此操作。为了确保用户不受此困扰，数据缓存如下:

//using Nlog to log caching behaviour
private Logger log = LogManager.GetCurrentClassLogger();
//a public actionresult to get the summaries with an ajax call or site24x7 service
public ActionResult GetSummariesAsync()
{
  log.Info(String.Format("GetSummariesAsync called"));
  List<ProjectDataSummary> summaries = GetAllSummaries();
  log.Info(String.Format("{0} summaries found", summaries.Count));
  List<ProjectDataSummary> cache = HttpContext.Cache["SummariesCache"] as List<ProjectDataSummary>;
  log.Info(String.Format("{0} in cache", cache.Count));
  return Json(summaries, JsonRequestBehavior.AllowGet);
}
private List<ProjectDataSummary> GetAllSummaries()
{
  List<ProjectDataSummary> summaries = new List<ProjectDataSummary>();
  //use setting in web.config if we want to force no cache, but set to false in released version
  if (ConfigurationManager.AppSettings["NoCache"] == "true")
  {
    summaries = _service.GetAllSummaries();
  }
  else
  {
    //get summaries from cache if available
    summaries = HttpContext.Cache["SummariesCache"] as List<ProjectDataSummary>;
    if (summaries == null)
    {
      //cache empty, retrieve values
      summaries = _service.GetAllSummaries();
      //cache it
      HttpContext.Cache.Add("SummariesCache", summaries, null, new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day, 23, 59, 59), Cache.NoSlidingExpiration, CacheItemPriority.NotRemovable, new CacheItemRemovedCallback(this.cacheCallback));
    }
  }
  return summaries;
}
private void cacheCallback(String K, Object v, CacheItemRemovedReason r)
{
  CacheItemRemovedReason reason = r;
  log.Info("Cache expired, reason: {0}", r.ToString());
}

我有一个来自www.site24x7.com的服务，每小时访问一次缓存创建，所以理论上它应该在上午0:00之后访问它，并使它创建另一个缓存。但是由于某些原因，缓存会被删除，网站每天会创建几次新的缓存，这也给用户带来了非常长的加载时间。

这是我的Nlog日志的一部分:

2015-09-22 18:31:07.8746 GetSummariesAsync Info GetSummariesAsync called 
2015-09-22 18:31:07.8901 GetSummariesAsync Info 263 summaries 
2015-09-22 18:31:07.8901 GetSummariesAsync Info 263 in cache 
2015-09-22 18:52:15.9684 cacheCallback Info Cache expired, reason: Removed 
2015-09-22 19:02:06.9839 cacheCallback Info Cache expired, reason: Removed 
2015-09-22 19:23:08.3590 cacheCallback Info Cache expired, reason: Removed 
2015-09-22 19:31:42.7182 GetSummariesAsync Info GetSummariesAsync called 
2015-09-22 19:32:15.0776 GetSummariesAsync Info GetSummariesAsync called 
2015-09-22 19:32:46.2495 GetSummariesAsync Info GetSummariesAsync called 
2015-09-22 19:33:01.8276 GetSummariesAsync Info GetSummariesAsync called 
2015-09-22 19:33:18.3746 GetSummariesAsync Info GetSummariesAsync called 
2015-09-22 19:33:34.8589 GetSummariesAsync Info GetSummariesAsync called 
2015-09-22 19:34:10.7182 GetSummariesAsync Info GetSummariesAsync called 
2015-09-22 19:34:15.4215 GetSummariesAsync Info 263 summaries 
2015-09-22 19:34:15.4215 GetSummariesAsync Info 263 in cache 
2015-09-22 19:35:07.3121 GetSummariesAsync Info 263 summaries 
2015-09-22 19:35:07.3121 GetSummariesAsync Info 263 in cache 
2015-09-22 19:36:07.9213 GetSummariesAsync Info 263 summaries 
2015-09-22 19:36:07.9213 GetSummariesAsync Info 263 in cache 
2015-09-22 19:36:19.5309 GetSummariesAsync Info 263 summaries 
2015-09-22 19:36:19.5309 GetSummariesAsync Info 263 in cache 
2015-09-22 19:36:36.3588 GetSummariesAsync Info 263 summaries 
2015-09-22 19:36:36.3588 GetSummariesAsync Info 263 in cache 
2015-09-22 19:37:07.9996 GetSummariesAsync Info 263 summaries 
2015-09-22 19:37:07.9996 GetSummariesAsync Info 263 in cache 
2015-09-22 19:37:33.7183 GetSummariesAsync Info 263 summaries 
2015-09-22 19:37:33.7183 GetSummariesAsync Info 263 in cache 
2015-09-22 19:37:59.8747 GetSummariesAsync Info GetSummariesAsync called 
2015-09-22 19:37:59.8747 GetSummariesAsync Info 263 summaries 
2015-09-22 19:37:59.8747 GetSummariesAsync Info 263 in cache 
2015-09-22 19:44:00.2496 cacheCallback Info Cache expired, reason: Removed 
2015-09-22 19:54:25.2183 cacheCallback Info Cache expired, reason: Removed 
2015-09-22 20:34:55.3589 GetSummariesAsync Info GetSummariesAsync called 
2015-09-22 20:34:55.3745 GetSummariesAsync Info 263 summaries 
2015-09-22 20:34:55.3745 GetSummariesAsync Info 263 in cache 
2015-09-22 20:44:32.5153 cacheCallback Info Cache expired, reason: Removed 
2015-09-22 20:56:38.8746 cacheCallback Info Cache expired, reason: Removed

编辑

我已经实现了NightOwl888给出的答案，但无济于事，缓存不断被删除。

这是我当前Nlog文件中的一段:

2015-09-27 20:05:29.9682 Controllers.HomeController.GetSummariesAsync Info 263 summaries found 
2015-09-27 20:05:29.9682 Controllers.HomeController.GetSummariesAsync Info 263 in cache found 
2015-09-27 20:23:51.5464 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed 
2015-09-27 20:23:51.5464 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed 
2015-09-27 20:23:51.5464 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed 
2015-09-27 20:25:48.1714 Models.CachingBase`1.GetItemsCache Info Cache fileEntries created 
2015-09-27 20:25:48.1714 Models.CachingBase`1.GetItemsCache Info Cache idCertificaat created 
2015-09-27 20:26:46.3588 Controllers.HomeController.Index Info No cache found, Home/Index needs to create the cash Async 
2015-09-27 20:26:46.7963 Controllers.HomeController.GetSummariesAsync Info GetSummariesAsync triggered by User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:40.0) Gecko/20100101 Firefox/40.0 vanuit Host: 88.159.95.251 
2015-09-27 20:27:26.9682 Models.CachingBase`1.GetItemsCache Info Cache GebouwProjectenSummaries created 
2015-09-27 20:27:26.9682 Controllers.HomeController.GetSummariesAsync Info 263 summaries found 
2015-09-27 20:27:26.9682 Controllers.HomeController.GetSummariesAsync Info 263 in cache found 
2015-09-27 20:33:48.7340 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed 
2015-09-27 20:33:48.7340 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed 
2015-09-27 20:33:48.7340 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed 
2015-09-27 20:38:21.0151 Models.CachingBase`1.GetItemsCache Info Cache fileEntries created 
2015-09-27 20:38:21.0151 Models.CachingBase`1.GetItemsCache Info Cache idCertificaat created 
2015-09-27 20:38:21.0620 Controllers.HomeController.Index Info No cache found, Home/Index needs to create the cash Async 
2015-09-27 20:43:41.0620 Controllers.HomeController.Index Info No cache found, Home/Index needs to create the cash Async 
2015-09-27 20:46:29.0620 Models.CachingBase`1.GetItemsCache Info Cache GebouwProjectenSummaries created 
2015-09-27 20:57:21.5776 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed 
2015-09-27 20:57:21.5776 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed 
2015-09-27 20:57:21.5776 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed 
2015-09-27 20:58:23.9553 Models.CachingBase`1.GetItemsCache Info Cache fileEntries created 
2015-09-27 20:58:23.9553 Models.CachingBase`1.GetItemsCache Info Cache idCertificaat created 
2015-09-27 20:58:23.9839 Controllers.HomeController.Index Info No cache found, Home/Index needs to create the cash Async 
2015-09-27 21:04:24.5151 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed 
2015-09-27 21:04:24.5151 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed 
2015-09-27 21:05:31.8277 Models.CachingBase`1.GetItemsCache Info Cache fileEntries created 
2015-09-27 21:05:31.8277 Models.CachingBase`1.GetItemsCache Info Cache idCertificaat created 
2015-09-27 21:05:31.8432 Controllers.HomeController.GetSummariesAsync Info GetSummariesAsync triggered by User-Agent: Site24x7 vanuit Host: 72.5.230.111 
2015-09-27 21:06:03.5307 Controllers.HomeController.GetSummariesAsync Info GetSummariesAsync triggered by User-Agent: Site24x7 vanuit Host: 72.5.230.111 
2015-09-27 21:06:36.3433 Controllers.HomeController.GetSummariesAsync Info GetSummariesAsync triggered by User-Agent: Site24x7 vanuit Host: 120.138.27.125 
2015-09-27 21:06:40.2651 Controllers.HomeController.GetSummariesAsync Info GetSummariesAsync triggered by User-Agent: Site24x7 vanuit Host: 119.81.237.98 
2015-09-27 21:07:08.6401 Controllers.HomeController.GetSummariesAsync Info GetSummariesAsync triggered by User-Agent: Site24x7 vanuit Host: 120.138.27.125 
2015-09-27 21:07:11.4057 Models.CachingBase`1.GetItemsCache Info Cache GebouwProjectenSummaries created 
2015-09-27 21:07:11.4057 Controllers.HomeController.GetSummariesAsync Info 263 summaries found 
2015-09-27 21:07:11.4057 Controllers.HomeController.GetSummariesAsync Info 263 summaries found 
2015-09-27 21:07:11.4057 Controllers.HomeController.GetSummariesAsync Info 263 in cache found 
2015-09-27 21:07:11.4057 Controllers.HomeController.GetSummariesAsync Info 263 in cache found 
2015-09-27 21:07:11.4214 Controllers.HomeController.GetSummariesAsync Info 263 summaries found 
2015-09-27 21:07:11.4214 Controllers.HomeController.GetSummariesAsync Info 263 in cache found 
2015-09-27 21:07:11.4214 Controllers.HomeController.GetSummariesAsync Info 263 summaries found 
2015-09-27 21:07:11.4214 Controllers.HomeController.GetSummariesAsync Info 263 in cache found 
2015-09-27 21:07:11.4214 Controllers.HomeController.GetSummariesAsync Info 263 summaries found 
2015-09-27 21:07:11.4214 Controllers.HomeController.GetSummariesAsync Info 263 in cache found 
2015-09-27 21:07:12.5620 Controllers.HomeController.GetSummariesAsync Info GetSummariesAsync triggered by User-Agent: Site24x7 vanuit Host: 119.81.237.98 
2015-09-27 21:07:12.5620 Controllers.HomeController.GetSummariesAsync Info 263 summaries found 
2015-09-27 21:07:12.5620 Controllers.HomeController.GetSummariesAsync Info 263 in cache found 
2015-09-27 21:15:32.4370 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed 
2015-09-27 21:15:32.4370 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed 
2015-09-27 21:15:32.4370 Controllers.HomeController.cacheCallback Info Cache expired, reason: Removed

您可以看到Site24x7有时会在一行中多次调用GetSummariesAsync函数。

用户也会(尽管很少)遇到问题。

从创造现金到移除现金的时间可以短至8分钟。

我现在已经禁用了site24x7检查，看看这是否是罪魁祸首

是什么导致我的httpcontext.缓存将被删除在我的c# MVC web应用程序

我不知道这是否是你的问题的根源，但我看到你有一个由多个线程调用你的GetAllSummaries方法引起的竞争条件。

当多个线程正在填充缓存时(由于冲突而删除了多余的条目)，您可能会得到错误的日志条目，并且用户只是因为多个线程在填充缓存之前竞争系统资源而遇到问题。

首先，看一下缓存的文档。添加方法:

如果具有相同键参数的项已经存储在缓存中，则调用此方法将失败。要使用相同的键参数覆盖现有的缓存项，请使用Insert方法。

更重要的是:

如果您使用Add方法，并且缓存中已经存在同名的项，则该方法不会替换该项，并且不会引发异常。

(重点)

此外，您的缓存检查代码不是线程安全的。多个线程可以运行GetAllSummaries方法，因为缓存在第一次调用返回之前没有值。而且由于Add方法不会因为重复而抛出异常，所以这些努力只是浪费。

你可以通过:

创建一个对象来包装缓存，以使对缓存的多次调用线程安全。
使用双重检查锁定模式，以确保只有一个线程可以通过获取数据。
使用缓存包装器的静态实例，确保所有线程使用相同的线程锁定代码。

SummariesCache

public sealed class SummariesCache
{
    private ReaderWriterLockSlim synclock = 
        new ReaderWriterLockSlim(LockRecursionPolicy.NoRecursion);
    public List<ProjectSummaryData> GetSummaries(
        ISummariesService service, 
        ref CacheItemRemovedCallback onRemoveCallback)
    {
        List<ProjectDataSummary> summaries;
        string key = "SummariesCache";
        bool success;
        synclock.EnterReadLock();
        try
        {
            success = TryGetCacheValue(key, out summaries);
        }
        finally
        {
            synclock.ExitReadLock();
        }
        if (!success)
        {
            synclock.EnterWriteLock();
            try
            {
                if (!TryGetCacheValue(key, out summaries))
                {
                    //cache empty, retrieve values
                    summaries = service.GetAllSummaries();
                    // load the cache (using Insert)
                    HttpContext.Current.Cache.Insert(
                        key, 
                        summaries, 
                        null, 
                        new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day, 23, 59, 59), 
                        Cache.NoSlidingExpiration, 
                        CacheItemPriority.NotRemovable, 
                        onRemoveCallback
                    );
                }
            }
            finally
            {
                synclock.ExitWriteLock();
            }
        }
        return summaries;
    }
    private bool TryGetCacheValue(string key, out List<ProjectSummaryData> value)
    {
        value = HttpContext.Current.Cache["key"] as List<ProjectDataSummary>;
        if (value != null)
        {
            return true;
        }
        return false;
    }
}

使用

// Use a static instance of the cache to ensure all threads use it.
private static _summariesCache = new SummariesCache();
private List<ProjectDataSummary> GetAllSummaries()
{
    List<ProjectDataSummary> summaries = new List<ProjectDataSummary>();
    //use setting in web.config if we want to force no cache, but set to false in released version
    if (ConfigurationManager.AppSettings["NoCache"] == "true")
    {
        summaries = _service.GetAllSummaries();
    }
    else
    {
        summaries = _summariesCache.GetSummaries(_service, new CacheItemRemovedCallback(cacheCallback));
    }
    return summaries;
}
private void cacheCallback(String K, Object v, CacheItemRemovedReason r)
{
    CacheItemRemovedReason reason = r;
    log.Info("Cache expired, reason: {0}", r.ToString());
}

注意:大部分代码是从。net的微缓存中借用的。如果你愿意，你可以使用那个解决方案。

HttpContext。缓存仅在应用程序的生命周期内可用，并且该生命周期与IIS应用程序池绑定。当应用程序池回收或终止时，缓存将被清除。不幸的是，您无法控制IIS何时执行此操作。在我的脑海中，我可以看到2个选项，或者(可能是两者的混合)。

将缓存存储在本地数据库中。仍然会比内存缓存慢，但可能比web服务快。
在应用程序启动时重新加载缓存(在Global的Application_Start()函数中)。

如果这个答案没有帮助，我很抱歉，但是我以前见过类似的问题，所以我想我应该发布。

我以前看到过一个问题，当日志记录器(在本例中是nlog)实际写入应用程序目录，特别是bin文件夹时。通过这样做，它实际上会触发网站重新加载其域逻辑，导致会话和缓存数据无效。

再次抱歉，如果这对你没有帮助，但我认为这是值得提及的