How to "block" in an agnostic way?

[gasche]

I believe that (3) is the only sensible option here, at least if you want to provide transactional guarantees (from the suspender side: either the resource we were waiting for was produced, and we run, or cancellation happened and the resource was not produced / not wasted.) I tried to discuss this in Understanding cancellation (in eio) - #16 by gasche