[throwawaymaths]

it's certainly possible to write a nif that cooperates with the VM so that its async yield points match up with the VM's expectation of yield points. Definitely tricky to do correctly in C (given that C doesn't have a yield statement, lol, you have to structure it as an awkward tail call where you pickle/unpickle whatever state you want to keep around or unmarshal it from a passed struct). I'm not sure if that's so easy to do in rust.

[toast0]

Sure, you can do that for the code you write, but you can't for the code you call. Any Erlang you write or call will have this property, and most of the ERTS provided C code will as well; either it's trivially finite, it is designed to yield during the work, or it's neither but it hasn't triggered anyone to fix it, with occasional deviations of things that become known issues (like -- was for some time; although it got fixed twice and is now fairly ok).