Generic .net cache....

Cache.cs

class Cache<T> where T : someBaseType
    {
        public readonly TimeSpan LifeSpan;
        public readonly SemaphoreSlim semaphore;

        private Dictionary<string, CacheItem<T>> itemDict;

        public Cache(TimeSpan lifespan)
        {
            this.LifeSpan = lifespan;
            itemDict = new Dictionary<string, CacheItem<T>>();
            semaphore = new SemaphoreSlim(1, 1);
        }

        //you can have async methods as well... semaphore.WaitAsync()
        public T Save(T item)
        {
            try
            {
                semaphore.Wait();
                itemDict[item.UniqueId] = new CacheItem<T>(item);
                return item;
            }
            finally
            {
                semaphore.Release();
            }
        }

        public T Invalidate(T item)
        {
            try
            {
                semaphore.Wait();
                if (itemDict.ContainsKey(item.UniqueId)) itemDict.Remove(item.UniqueId);
                return item;
            }
            finally
            {
                semaphore.Release();
            }
        }

        public T Fetch(T item)
        {
            try
            {
                semaphore.Wait();
                if (itemDict.ContainsKey(item.UniqueId))
                {
                    var cacheItem = itemDict[item.UniqueId];
                    if (DateTime.Now.Subtract(cacheItem.Created) > LifeSpan)
                    {
                        itemDict.Remove(item.UniqueId);
                        return null;
                    }
                    return cacheItem.Item;
                }
                return null;
            }
            finally
            {
                semaphore.Release();
            }
        }
    }

    class CacheItem<T> where T : someBaseType
    {
        public readonly DateTime Created;
        public readonly T Item;

        public CacheItem(T item)
        {
            this.Item = item;
            this.Created = DateTime.Now;
        } 
    }