That angle seems potentially insightful, and I'm going to have to think about it, but to me, cache invalidation seems more like replacing one logical thing with nothing. It may or may not get replaced with a new version of the same logical thing later if that's required.
To me, cache invalidation is not strictly about either replacing or removing cache entries.
Rather, cache invalidation is the process of determining which cache entries are stale and need to be replaced/removed.
It gets hairy when determining that depends on users, user group memberships AND per-user permissions, access TTL, multiple types of timestamps and/or revision numbering, and especially when the cache entries are composite as in contain data from multiple database entities, where some are e.g. representing a hierarchy and may not even have direct entity relationships with the cached data.
Are they really? TOCTOU is a trigger for race conditions, but I guess the result of the check is a cached value. Then again, the issue in TOCTOU is that the ”cached value” is not invalidated at all, or inadequately. It doesn’t really have anything to do with the invalidation mechanism, it is downstream from it.
I think it's sort of subjective. The fact that the invalidation mechanism doesn't extend further downstream is a problem with it, from my point of view, but maybe not yours. It's difficult to provide indisputable proofs of such value judgments.
