er code.
</p>
<p>Where a file watch on a file descriptor or port has been added with
event-loop-add-read-watch! or event-loop-add-write-watch!, the event
loop should be treated as owning the descriptor or port until it has
subsequently been removed with event-loop-remove-read-watch! or
event-loop-remove-write-watch!.  In particular, if the watch is on a
port, an error in the fileno or select procedures will arise at some
point if the port is closed (say by calling close, close-port,
close-input-port or clos