public static class CacheHelper

{

    private static readonly Object _locker = new object();

    public static T GetCacheItem<T>(String key, Func<T> cachePopulate, TimeSpan? slidingExpiration = null, DateTime? absoluteExpiration = null)

    {

        if(String.IsNullOrWhiteSpace(key)) throw new ArgumentException("Invalid cache key");

        if(cachePopulate == null) throw new ArgumentNullException("cachePopulate");

        if(slidingExpiration == null && absoluteExpiration == null) throw new ArgumentException("Either a sliding expiration or absolute must be provided");

        if(MemoryCache.Default[key] == null)

        {

            lock(_locker)

            {

                if(MemoryCache.Default[key] == null)

                {

                    var item = new CacheItem(key, cachePopulate());

                    var policy = CreatePolicy(slidingExpiration, absoluteExpiration);

                    MemoryCache.Default.Add(item, policy);

                }

            }

        }

        return (T)MemoryCache.Default[key];

    }

    private static CacheItemPolicy CreatePolicy(TimeSpan? slidingExpiration, DateTime? absoluteExpiration)

    {

        var policy = new CacheItemPolicy();

        if(absoluteExpiration.HasValue)

        {

            policy.AbsoluteExpiration = absoluteExpiration.Value;

        }

        else if(slidingExpiration.HasValue)

        {

            policy.SlidingExpiration = slidingExpiration.Value;

        }

        policy.Priority = CacheItemPriority.Default;

        return policy;

    }

}