Blog Code: Efficient Thread-Safe Caching with ASP.NET

CacheManager.cs

public class CacheManager
{
    // CLR guarantees thread-safety during initialization
    private static Dictionary<string, object> CacheKeyDictionary = new Dictionary<string, object>();
 
    public static TObj GetCachedObject<TObj>(string cacheKey, Func<TObj> creator) where TObj : class
    {
        var cache = HttpContext.Current.Cache;
        var obj = cache[cacheKey] as TObj;
 
        if (obj == null)
        {
            // get the lock object
            var lockObject = GetCacheLockObject(cacheKey);
            lock (lockObject)
            {
                // double check...if-lock-if
                obj = cache[cacheKey] as TObj;
 
                if (obj == null)
                {
                    obj = creator.Invoke();
                    cache.Insert(cacheKey, obj);
                }
            }
        }
 
        return obj;
    }
 
    private static object GetCacheLockObject(string cacheKey)
    {
        if (!CacheKeyDictionary.ContainsKey(cacheKey))
        {
            // lock on the whole dictionary
            lock (CacheKeyDictionary)
            {
                // check again...always remember: if-lock-if
                if (!CacheKeyDictionary.ContainsKey(cacheKey))
                {
                    CacheKeyDictionary.Add(cacheKey, new object());
                }
            }
        }
 
        return CacheKeyDictionary[cacheKey];
    }
}

ClientCode.cs

private IEnumerable<string> GetExpensiveNameList()
{
    return CacheManager.GetCachedObject<IEnumerable<string>>(
            "CacheKeyHere",
            () =>
            {
                // perform expensive lookup here...
                return Enumerable.Empty<string>();
            }
        );
}

if_lock_if_cache.cs

private TObj GetCachedObject<TObj>(string cacheKey, Func<TObj> creator) where TObj : class
{
    Cache cache = this.HttpContext.Cache;
    TObj obj = cache[cacheKey] as TObj;
 
    if (obj == null)
    {
        lock (cache)
        {
            //look it up again in case a previous request created it already
            obj = cache[cacheKey] as TObj;
 
            if (obj == null)
            {
                obj = creator.Invoke();
                cache.Insert(cacheKey, obj);
            }
        }
    }
 
    return obj;
}

locked_cache.cs

private TObj GetCachedObject<TObj>(string cacheKey, Func<TObj> creator) where TObj : class
{
    Cache cache = this.HttpContext.Cache;
    TObj obj = cache[cacheKey] as TObj;
 
    if (obj == null)
    {
        lock (cache)
        {
            obj = creator.Invoke();
            cache.Insert(cacheKey, obj);
        }
    }
 
    return obj;
}

naive_cache.cs

private TObj GetCachedObject<TObj>(string cacheKey, Func<TObj> creator) where TObj : class
{
    TObj obj = this.HttpContext.Cache[cacheKey] as TObj;
 
    if (obj == null)
    {
        obj = creator.Invoke();
        this.HttpContext.Cache.Insert(cacheKey, obj);
    }
 
    return obj;
}

Thank you very much for this! It really helped.