for high contrast, but you can tell that I just changed the <code>l_type</code> field to <code>F_UNLCK</code> (leaving the others completely unchanged!) and called <code>fcntl()</code> with <code>F_SETLK</code> as the command. Easy!</p>
<h2 data-number="6.3" id="a-demo-program"><span class="header-section-number">6.3</span> A demo program</h2>
<p>Here, I will include a demo program, <code>lockdemo.c</code>, that waits for the user to hit return, then locks its own source, waits for another return, then unlo