Running code once and only once
It occasionally pops up---you have a piece of code you need to run once, but only once, even requested from multiple threads simultaneously. It's not a difficult problem, but can be boring enough to be worth to have a library procedure on some languages.
Every time I encounter an instance of such case it occurs to me to add a library procedure, then I think again to drop the idea, for it's just as trivial as the following in Scheme:
(define (run-once thunk) (let1 v (delay (thunk)) (^ (force v))))
(It may depend on implementations, but at least
thread-safe and the above just works in multi-threaded environment.)
Do you think it is worth to have it in a library?