O_NONBLOCK
                      (fcntl [port] F_GETFL)))
</pre></div>

<p>The &rsquo;loop&rsquo; argument is optional: this procedure operates on the event
loop passed in as an argument, or if none is passed (or #f is passed),
on the default event loop.
</p>
<p>This procedure must (like the a-sync procedure) be called in the same
thread as that in which the event loop runs.
</p>
<p>When &rsquo;proc&rsquo; executes, &rsquo;await&rsquo; and &rsquo;resume&rsquo; will still be in use by
this procedure, so they