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POErlang - Dining Philosophers errors
 

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    <p>I apologize if the code is hard to follow. This is the classic dining philosophers problem, where 5 philosophers are eating, but there are only 5 sticks - and you need two to eat. </p> <p>These are the instructions, if anyone is interested: <a href="http://www.kth.se/polopoly_fs/1.260940!/Menu/general/column-content/attachment/philosophers.pdf" rel="nofollow">http://www.kth.se/polopoly_fs/1.260940!/Menu/general/column-content/attachment/philosophers.pdf</a></p> <p>Anyways, here is the code, the chopstick process code:</p> <pre><code>-module(chopstick). -export([start/0]). start() -&gt; spawn_link(fun() -&gt; init() end). init() -&gt; available(). available() -&gt; receive {request, From} -&gt; From ! granted, gone(); quit -&gt; ok end. gone() -&gt; receive returned -&gt; available(); quit -&gt; ok end. </code></pre> <p>The philosopher process code:</p> <pre><code>-module(eater). -import(timer, [sleep/1]). -import(random, [uniform/1]). -export([start/5, dream/5, eat/5, wait/5]). start(Hungry, Right, Left, Name, Ctrl) -&gt; dream(Hungry, Right, Left, Name, Ctrl). **%This was wrong, it should say start(Hungry, Right, Left, Name, Ctrl) -&gt; spawn_link(fun() -&gt; dream(Hungry, Right, Left, Name, Ctrl) end).** dream(Hungry, Right, Left, Name, Ctrl) -&gt; Time = 500+uniform:random(500), **%This was wrong, it should say random:uniform** timer:sleep(Time), Right! {request, self()}, Left! {request, self()}, %skicka {request, self()} till två pinnar wait(Hungry, Right, Left, Name, Ctrl). wait(Hungry, Right, Left, Name, Ctrl) -&gt; receive granted -&gt; io:format("~s received a chopstick~n", [Name]), receive granted -&gt; io:format("~s received a chopstick~n", [Name]), io:format("~s started eating~n", [Name]), eat(Hungry, Right, Left, Name, Ctrl) end; _ -&gt; wait(Hungry, Right, Left, Name, Ctrl) end. eat(Hungry, Right, Left, Name, Ctrl) -&gt; Time = 500+uniform:random(500), **%This was wrong, it should say random:uniform** timer:sleep(Time), Right! returned, Left! returned, io:format("~s put back two chopsticks~n", [Name]), if Hungry =&lt; 1 -&gt; Ctrl ! done; true -&gt; dream(Hungry-1, Right, Left, Name, Ctrl) end. </code></pre> <p>And finally the host process:</p> <pre><code>-module(dinner). -export([start/0]). start() -&gt; spawn(fun() -&gt; init() end). init() -&gt; C1 = chopstick:start(), C2 = chopstick:start(), C3 = chopstick:start(), C4 = chopstick:start(), C5 = chopstick:start(), Ctrl = self(), eater:start(5, C1, C2, "Confucios", Ctrl), **% This is where it crashes** eater:start(5, C2, C3, "Avicenna", Ctrl), eater:start(5, C3, C4, "Plato", Ctrl), eater:start(5, C4, C5, "Kant", Ctrl), eater:start(5, C5, C1, "Descartes", Ctrl), wait(5, [C1, C2, C3, C4, C5]). wait(0, Chopsticks) -&gt; lists:foreach(fun(C) -&gt; C ! quit end, Chopsticks); wait(N, Chopsticks) -&gt; receive done -&gt; wait(N-1, Chopsticks); abort -&gt; erlang:exit(abort) end. </code></pre> <p>Output:</p> <pre><code>11&gt; dinner:start(). &lt;0.85.0&gt; 12&gt; =ERROR REPORT==== 10-Nov-2011::02:19:10 === Error in process &lt;0.85.0&gt; with exit value: {undef,[{uniform,random,[500]}, {eater,dream,5},{dinner,init,0}]} </code></pre> <p>Thanks a lot if you even read through all of this, I haven't learnt how to read the error reports of erlang yet. If you can, and want to tell me what it means please do.</p>
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