System.Runtime.Cache expires instantly

Question

I have a webpage which caches some querystring values for 30 seconds so that it does not receive duplicate values. I am using the following class:

public class MyCache   {

private static ObjectCache cache = MemoryCache.Default;

public MyCache() { }


public void Insert(string key, string value)
{

    CacheItemPolicy policy = new CacheItemPolicy();
    policy.Priority = CacheItemPriority.Default;
    policy.SlidingExpiration = new TimeSpan(0, 0, 30);
    policy.RemovedCallback = new CacheEntryRemovedCallback(this.Cacheremovedcallback);

    cache.Set(key, value, policy);
}

public bool Exists(string key)
{
    return cache.Contains(key);
}

public void Remove(string key)
{
    cache.Remove(key);
}

private void Cacheremovedcallback(CacheEntryRemovedArguments arguments)
{      
    FileLog.LogToFile("Cache item removed. Reason: " + arguments.RemovedReason.ToString() +  "; Item: [" +  arguments.CacheItem.Key + ", " + arguments.CacheItem.Value.ToString() + "]");         
}
 }

This has worked fine for a couple of weeks then suddenly the cache doesn't keep the values anymore. The CacheRemoved callback fires instantly after an item is inserted into cache and i get the removed reason: CacheSpecificEviction This is running on a Windows Server 2008 SP1, IIS7.5 with .NET 4.0. No changes were applied to the OS or IIS during this time.

Is there a way to solve this and if not, is there a better cache solution to use in a web page ?

Thank you in advance.

Answer 1

Looking at the source code of MemoryCacheStore (that should be the default store used by MemoryCache.Default) it seems that the remove callback with argument CacheSpecificEviction is only called when the cache is disposed:

https://referencesource.microsoft.com/#System.Runtime.Caching/System/Caching/MemoryCacheStore.cs,230

Look around and make sure your cache object is not being disposed accidentally.