In C++, which Standard Library functions (if any) are required to implicitly provided an atomic memory fence?

Question

For example, is calling std::mutex::lock() required by the Standard to provide a sequentially consistent fence, an acquire fence, or neither?

cppreference.com doesn't seem to address this topic. Is it addressed in any reference documentation that's more easy to use than the Standard or working papers?

Answer 1

I'm not sure about an easier source, but here's a quote from a note in the standard:

[...] a call that acquires a mutex will perform an acquire operation on the locations comprising the mutex. Correspondingly, a call that releases the same mutex will perform a release operation on those same locations. Informally, performing a release operation on A forces prior side effects on other memory locations to become visible to other threads that later perform a consume or an acquire operation on A.

I think that answers the question about memory fences reasonably well (and although it's "only" a note, not a normative part of the standard, I'd say it's as reliable a description of the standard as any other site could hope to provide).