True, generic test-and-set ops can be used. But what about if there is already a request in-flight? Do you wait or fail? What is the experience working with eit

True, generic test-and-set ops can be used. But what about if there is already a request in-flight? Do you wait or fail? What is the experience working with either? What is the experience invalidation the cache key? And similar other questions :) So more practical than theoretical side to idempotency