ASP.net Cache Absolute Expiration not working

Question

I am storing a single integer value in HttpContext.Cache with an absolute expiration time of 5 minutes from now. However, after waiting 6 minutes (or longer), the integer value

Answer 1

It turns out that this line:

HttpContext.Current.Cache[remoteIp] = ((int)HttpContext.Current.Cache[remoteIp]) + 1;

removes the previous value and re-inserts the value with NO absolute or sliding expiration time. In order to get around this I had to create a helper class and use it like so:

public class IncrementingCacheCounter
{
    public int Count;
    public DateTime ExpireDate;
}

public void UpdateCountFor(string remoteIp)
{
    IncrementingCacheCounter counter = null;
    if (HttpContext.Current.Cache[remoteIp] == null)
    {
        var expireDate = DateTime.Now.AddMinutes(5);
        counter = new IncrementingCacheCounter { Count = 1, ExpireDate = expireDate };
    }
    else
    {
        counter = (IncrementingCacheCounter)HttpContext.Current.Cache[remoteIp];
        counter.Count++;
    }
    HttpContext.Current.Cache.Insert(remoteIp, counter, null, counter.ExpireDate, Cache.NoSlidingExpiration, CacheItemPriority.Default, null);
}

This will get around the issue and let the counter properly expire at the absolute time while still enabling updates to it.