Yes, CRITICAL_SECTION is far too large. Mara asked some years ago whether SRWLock could guarantee what Rust actually needs for this purpose (the documentation a

Yes, CRITICAL_SECTION is far too large. Mara asked some years ago whether SRWLock could guarantee what Rust actually needs for this purpose (the documentation at that time refused to clarify whether we can move it for example) and that's why her change was to SRWLock from CRITICAL_SECTION. And yes, the newer change uses WaitOnAddress to provide the same API as the futex from the various Unix platforms. Raymond Chen's description of the differences is perhaps rather exaggerated, which isn't to say there's no difference, but it's well within what's practical for an adaptor layer. Also although the SRWLock itself is the same size as a pointer (thus, 64 bits on a modern computer, compared to a 32-bit Futex) there's a reason it's the same size as a pointer - it actually is basically a pointer, and so in some cases it's pointing at a data structure which we should reasonably say is also part of the overhead. The pointer is to a large aligned object, which means the bottom bits would be zero and so SRWLock uses those for flag bits. It's a nice trick but we should remember that it isn't really comparable to a Futex though it's certainly cheaper than CRITICAL_SECTION.