> I think the key difference is that they only need to coordinate when the reader and writer are close together.

This was already the case with the cached index design at the end of the article, though. (Which doesn't require extra space or extra atomic stores.)

That's a good point. They are very similar. I guess the sentinel design in theory doesn't need to synchronize at all as long as there is a decent buffer between them. But the cached design synchronizes less commonly the more space there is which sounds like it would be very similar in practice. The sentinel design might also have a few thrashing issues when the reader and writer are on the same page which would probably be a bit less of an issue with the cached index design.