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| <!DOCTYPE html> | ||
| <html lang="en"> | ||
| <head> | ||
| <meta charset="utf-8"/> | ||
| <title>Deadlock</title> | ||
| <meta name="author" content="(Dr Carey Pridgeon)"/> | ||
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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"> | ||
| </div> | ||
| </section> | ||
| </section> | ||
| <section> | ||
| <section id="slide-sec-"> | ||
| <h3 id="org7bc8f87">Deadlock</h3> | ||
| <ul> | ||
| <li>What Deadlock is and how to avoid it.</li> | ||
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| </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> | ||
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| </ul> | ||
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| <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> | ||
|
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||
| </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> | ||
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| </ul> | ||
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| </section> | ||
| </section> | ||
| <section> | ||
| <section id="slide-sec-"> | ||
| <h3 id="org881b883">Obligatory XKCD</h3> | ||
|
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||
| <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> | ||
|
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||
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| #+TITLE: Deadlock | ||
| #+AUTHOR: Dr Carey Pridgeon | ||
| #+EMAIL: ab0475@coventry.ac.uk | ||
| * setup :noexport: | ||
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| #+STARTUP: showeverything | ||
| # Licenced under Creative Commons Attribution-ShareAlike 4.0 | ||
| # International by Dr Carey Pridgeon 2021 | ||
| * Deadlock | ||
| ** Deadlock | ||
| - What Deadlock is and how to avoid it. | ||
| ** | ||
| - This occurs when two or more threads need more than one shared resource in | ||
| order to complete a task. | ||
| [[file:img/deadlock.png]] | ||
| ** | ||
| - Unless access to these resources is strictly controlled by means of careful | ||
| program design, deadlock can easily happen. | ||
| ** Preventative measures | ||
| - *Condition Variables* | ||
| - 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. | ||
| - 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. | ||
| ** Curative Measures | ||
| - Here we have two options | ||
| - *Deadlock Breaking Algorithms* | ||
| - 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. | ||
| - *Redundant System* | ||
| - 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. | ||
|
|
||
|
|
||
|
|
||
| ** Obligatory XKCD | ||
| file:img/travelling_salesman_problem.png | ||
| - Copyright: Randall Munroe | ||
| - Mirrored to avoid bandwidth stealing | ||
| - This Lecture is Licensed under [[https://creativecommons.org/licenses/by-sa/4.0/][Creative Commons Attribution-ShareAlike 4.0 International]] | ||
| - By Dr Carey Pridgeon Coventry University, UK, 2021 |