os.preadv() and os.pwritev() are great but to my understanding one essential piece is still missing in order to effectively do non-blocking file IO and avoid using a thread pool: being notified when the file fd is readable/writable. select() and epoll() on Linux are not able to do that (according to them regular fds are always "ready"). As such one would repeatedly get EAGAIN and hog CPU resources. Am I missing something?