Cyclic data structures are in my experience very useful for concurrency. It's probably the number three good excuse for using a linked list, when you want to h

Cyclic data structures are in my experience very useful for concurrency. It's probably the number three good excuse for using a linked list, when you want to hold a lock for O(1) time with no shenanigans. But also, generally, anything that involves communicating information from point A to point B, and waiting on that information, involves some sort of cyclic reference between the sender and listener.