Every time someone writes something like this, I just wish Google open sourced its Fibers - that thing is sublime. Unfortunately that's not going to happen as the niceties that implementation affords require a modified kernel. I think I saw a presentation describing Fibers a few years back by one of its authors, but it's darn near impossible to find because there's also "Google Fiber". If someone has a link, please share. Fibers sort of opened up my mind to what's possible in this space if you go deeper than people usually go. They're also a source of dissatisfaction with how this turns out when people don't go as deep as the authors of Fibers did.
https://github.com/abseil/abseil-cpp/issues/5