Cache the output of a method call.

CacheExtensions.cs

public static class CacheExtensions
{
    private static readonly object ThisLock = new object();

    public static T Get<T>(this Cache cache, string key, Func<T> builder, DateTime expiration)
    {
        var data = cache.Get(key);
        if (data == null)
        {
            lock (ThisLock)
            {
                data = cache.Get(key);
                if (data == null)
                {
                    data = builder.Invoke();
                    cache.Add(key, data, null, expiration, Cache.NoSlidingExpiration, CacheItemPriority.Default, null);
                }
            }
        }
        return (T)data;
    }
}

Usage.cs

var cache = new Cache();
var value = cache.Get("MyKey", () => GetFooById(42), DateTime.Now.AddHours(3));

// The method to cache results from.
private string GetFooById(int id)
{ /* ... */ }