Abstraction is not very compatible with concurrency, so as well as your your beautiful abstract API, you also need some ‘cut through the layers’ functions to return the underlying classes you need to synchronise on. Now you have a right mess that’s incredibly hard to understand, infuriating to debug, and impossible to refactor. Best you can do is put another layer of abstraction on top. Repeat every six months.

Just need a chutney that was developed in the 90s, and then we can make a delicious chutney+blue ciabatta sandwich that’s all younger than you think.