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<title>Deadlock</title>
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<section id="sec-title-slide"><h1 class="title">Deadlock</h1><h2 class="author">Dr Carey Pridgeon</h2><p class="date">Created: 2021-01-26 Tue 15:46</p>
</section>
<section>
<section id="slide-sec-">
<h2 id="org4687d6c">Deadlock</h2>
<div class="outline-text-2" id="text-org4687d6c">
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</section>
</section>
<section>
<section id="slide-sec-">
<h3 id="org7bc8f87">Deadlock</h3>
<ul>
<li>What Deadlock is and how to avoid it.</li>
</ul>
</section>
</section>
<section>
<section id="slide-sec-">
<h3 id="org5ec0c5f"></h3>
<ul>
<li>This occurs when two or more threads need more than one shared resource in
order to complete a task.</li>
</ul>
<div class="figure">
<p><img src="img/deadlock.png" alt="deadlock.png" />
</p>
</div>
</section>
</section>
<section>
<section id="slide-sec-">
<h3 id="org4a642bb"></h3>
<ul>
<li>Unless access to these resources is strictly controlled by means of careful
program design, deadlock can easily happen.</li>
</ul>
</section>
</section>
<section>
<section id="slide-sec-">
<h3 id="org2def931">Preventative measures</h3>
<ul>
<li><b>Condition Variables</b>
<ul>
<li>By introducing an extra layer of control, being imposing order of access
rather than simply granting of access, Condition variables can go some way in
prevention of deadlock.</li>
</ul></li>
<li>They can also, if used correctly, be used to release resources if held for too
long without a complete set of requirements (all required resources) being
met. This is complex to code, and not something we can cover.</li>
</ul>
</section>
</section>
<section>
<section id="slide-sec-">
<h3 id="orgb6839cd">Curative Measures</h3>
<ul>
<li>Here we have two options</li>
<li><b>Deadlock Breaking Algorithms</b>
<ul>
<li>These act after the system in question has been in a state of deadlock for a
set period of time, typically numbered in milliseconds or less. It works by forcing
all resource gathering threads to let go of all of their resources and start
again. Essentially a soft reset.</li>
</ul></li>
<li><b>Redundant System</b>
<ul>
<li>The second option, cheaper and becoming more common as hardware gets cheaper,
is to emplace a duplicate system, running in parallel and ready to take over
if the first system locks up.</li>
</ul></li>
</ul>
</section>
</section>
<section>
<section id="slide-sec-">
<h3 id="org881b883">Obligatory XKCD</h3>
<div class="figure">
<p><img src="img/travelling_salesman_problem.png" alt="travelling_salesman_problem.png" />
</p>
</div>
<ul>
<li>Copyright: Randall Munroe</li>
<li>Mirrored to avoid bandwidth stealing</li>
<li>This Lecture is Licensed under <a href="https://creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike 4.0 International</a></li>
<li>By Dr Carey Pridgeon Coventry University, UK, 2021</li>
</ul>
</section>
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