eio/lib_eio_posix/test/poll.md

# #require "eio_posix";;

open Eio.Std

Closing an FD removes it from the multiplexer

Closing an FD automatically removes it from epoll's set, meaning that you have to re-add it using EPOLL_CTL_ADD, not EPOLL_CTL_MOD.

# Eio_posix.run @@ fun _env ->
  Switch.run (fun sw ->
     let r, w = Eio_unix.pipe sw in
     Eio_unix.await_writable (Eio_unix.FD.peek w)
  );
  (* [r] and [w] are now closed. We'll likely allocate the same FD numbers the second time.
     Check we don't get confused and try to [EPOLL_CTL_MOD] them. *)
  Switch.run (fun sw ->
     let r, w = Eio_unix.pipe sw in
     Eio_unix.await_writable (Eio_unix.FD.peek w)
  );;
- : unit = ()