POLL_ONEOFF

;;; Concurrently poll for the occurrence of a set of events.
  ;;;
  ;;; If `nsubscriptions` is 0, returns `errno::inval`.
  (@interface func (export "poll_oneoff")
    ;;; The events to which to subscribe.
    (param $in (@witx const_pointer $subscription))
    ;;; The events that have occurred.
    (param $out (@witx pointer $event))
    ;;; Both the number of subscriptions and events.
    (param $nsubscriptions $size)
    ;;; The number of events stored.
    (result $error (expected $size (error $errno)))
  )