I am a big fan of using Lazy<T> as my go-to implementation of the Singleton pattern. It works well and the thread safety is easily adjustable . While I won’t go into the details of how to use it, all the information is in the Lazy<T> documentation. For what I needed, however, Lazy<T> fell a bit short. I essentially needed a cache of something that was expensive to create, and could be invalidated when the source object changed. In my case, I had a list that I needed to run some aggregate queries against. Running those queries is expensive, so…