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<div class="section" id="machine-shop">
<h1>Machine Shop<a class="headerlink" href="#machine-shop" title="Permalink to this headline">¶</a></h1>
<p>Covers:</p>
<ul class="simple">
<li>Interrupts</li>
<li>Resources: PreemptiveResource</li>
</ul>
<p>This example comprises a workshop with <em>n</em> identical machines. A stream of jobs
(enough to keep the machines busy) arrives. Each machine breaks down
periodically. Repairs are carried out by one repairman. The repairman has
other, less important tasks to perform, too. Broken machines preempt theses
tasks. The repairman continues them when he is done with the machine repair.
The workshop works continuously.</p>
<p>A machine has two processes: <em>working</em> implements the actual behaviour of the
machine (producing parts). <em>break_machine</em> periodically interrupts the
<em>working</em> process to simulate the machine failure.</p>
<p>The repairman’s other job is also a process (implemented by <em>other_job</em>). The
repairman itself is a <a class="reference internal" href="../api_reference/simpy.resources.html#simpy.resources.resource.PreemptiveResource" title="simpy.resources.resource.PreemptiveResource"><code class="xref py py-class docutils literal"><span class="pre">PreemptiveResource</span></code></a>
with a capacity of <em>1</em>. The machine repairing has a priority of <em>1</em>, while the
other job has a priority of <em>2</em> (the smaller the number, the higher the
priority).</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="sd">"""</span>
<span class="sd">Machine shop example</span>
<span class="sd">Covers:</span>
<span class="sd">- Interrupts</span>
<span class="sd">- Resources: PreemptiveResource</span>
<span class="sd">Scenario:</span>
<span class="sd"> A workshop has *n* identical machines. A stream of jobs (enough to</span>
<span class="sd"> keep the machines busy) arrives. Each machine breaks down</span>
<span class="sd"> periodically. Repairs are carried out by one repairman. The repairman</span>
<span class="sd"> has other, less important tasks to perform, too. Broken machines</span>
<span class="sd"> preempt theses tasks. The repairman continues them when he is done</span>
<span class="sd"> with the machine repair. The workshop works continuously.</span>
<span class="sd">"""</span>
<span class="kn">import</span> <span class="nn">random</span>
<span class="kn">import</span> <span class="nn">simpy</span>
<span class="n">RANDOM_SEED</span> <span class="o">=</span> <span class="mi">42</span>
<span class="n">PT_MEAN</span> <span class="o">=</span> <span class="mf">10.0</span> <span class="c1"># Avg. processing time in minutes</span>
<span class="n">PT_SIGMA</span> <span class="o">=</span> <span class="mf">2.0</span> <span class="c1"># Sigma of processing time</span>
<span class="n">MTTF</span> <span class="o">=</span> <span class="mf">300.0</span> <span class="c1"># Mean time to failure in minutes</span>
<span class="n">BREAK_MEAN</span> <span class="o">=</span> <span class="mi">1</span> <span class="o">/</span> <span class="n">MTTF</span> <span class="c1"># Param. for expovariate distribution</span>
<span class="n">REPAIR_TIME</span> <span class="o">=</span> <span class="mf">30.0</span> <span class="c1"># Time it takes to repair a machine in minutes</span>
<span class="n">JOB_DURATION</span> <span class="o">=</span> <span class="mf">30.0</span> <span class="c1"># Duration of other jobs in minutes</span>
<span class="n">NUM_MACHINES</span> <span class="o">=</span> <span class="mi">10</span> <span class="c1"># Number of machines in the machine shop</span>
<span class="n">WEEKS</span> <span class="o">=</span> <span class="mi">4</span> <span class="c1"># Simulation time in weeks</span>
<span class="n">SIM_TIME</span> <span class="o">=</span> <span class="n">WEEKS</span> <span class="o">*</span> <span class="mi">7</span> <span class="o">*</span> <span class="mi">24</span> <span class="o">*</span> <span class="mi">60</span> <span class="c1"># Simulation time in minutes</span>
<span class="k">def</span> <span class="nf">time_per_part</span><span class="p">():</span>
<span class="sd">"""Return actual processing time for a concrete part."""</span>
<span class="k">return</span> <span class="n">random</span><span class="o">.</span><span class="n">normalvariate</span><span class="p">(</span><span class="n">PT_MEAN</span><span class="p">,</span> <span class="n">PT_SIGMA</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">time_to_failure</span><span class="p">():</span>
<span class="sd">"""Return time until next failure for a machine."""</span>
<span class="k">return</span> <span class="n">random</span><span class="o">.</span><span class="n">expovariate</span><span class="p">(</span><span class="n">BREAK_MEAN</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">Machine</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="sd">"""A machine produces parts and my get broken every now and then.</span>
<span class="sd"> If it breaks, it requests a *repairman* and continues the production</span>
<span class="sd"> after the it is repaired.</span>
<span class="sd"> A machine has a *name* and a numberof *parts_made* thus far.</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">env</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">repairman</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">env</span> <span class="o">=</span> <span class="n">env</span>
<span class="bp">self</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="n">name</span>
<span class="bp">self</span><span class="o">.</span><span class="n">parts_made</span> <span class="o">=</span> <span class="mi">0</span>
<span class="bp">self</span><span class="o">.</span><span class="n">broken</span> <span class="o">=</span> <span class="kc">False</span>
<span class="c1"># Start "working" and "break_machine" processes for this machine.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">process</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="n">process</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">working</span><span class="p">(</span><span class="n">repairman</span><span class="p">))</span>
<span class="n">env</span><span class="o">.</span><span class="n">process</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">break_machine</span><span class="p">())</span>
<span class="k">def</span> <span class="nf">working</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">repairman</span><span class="p">):</span>
<span class="sd">"""Produce parts as long as the simulation runs.</span>
<span class="sd"> While making a part, the machine may break multiple times.</span>
<span class="sd"> Request a repairman when this happens.</span>
<span class="sd"> """</span>
<span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
<span class="c1"># Start making a new part</span>
<span class="n">done_in</span> <span class="o">=</span> <span class="n">time_per_part</span><span class="p">()</span>
<span class="k">while</span> <span class="n">done_in</span><span class="p">:</span>
<span class="k">try</span><span class="p">:</span>
<span class="c1"># Working on the part</span>
<span class="n">start</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">env</span><span class="o">.</span><span class="n">now</span>
<span class="k">yield</span> <span class="bp">self</span><span class="o">.</span><span class="n">env</span><span class="o">.</span><span class="n">timeout</span><span class="p">(</span><span class="n">done_in</span><span class="p">)</span>
<span class="n">done_in</span> <span class="o">=</span> <span class="mi">0</span> <span class="c1"># Set to 0 to exit while loop.</span>
<span class="k">except</span> <span class="n">simpy</span><span class="o">.</span><span class="n">Interrupt</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">broken</span> <span class="o">=</span> <span class="kc">True</span>
<span class="n">done_in</span> <span class="o">-=</span> <span class="bp">self</span><span class="o">.</span><span class="n">env</span><span class="o">.</span><span class="n">now</span> <span class="o">-</span> <span class="n">start</span> <span class="c1"># How much time left?</span>
<span class="c1"># Request a repairman. This will preempt its "other_job".</span>
<span class="k">with</span> <span class="n">repairman</span><span class="o">.</span><span class="n">request</span><span class="p">(</span><span class="n">priority</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="k">as</span> <span class="n">req</span><span class="p">:</span>
<span class="k">yield</span> <span class="n">req</span>
<span class="k">yield</span> <span class="bp">self</span><span class="o">.</span><span class="n">env</span><span class="o">.</span><span class="n">timeout</span><span class="p">(</span><span class="n">REPAIR_TIME</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">broken</span> <span class="o">=</span> <span class="kc">False</span>
<span class="c1"># Part is done.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">parts_made</span> <span class="o">+=</span> <span class="mi">1</span>
<span class="k">def</span> <span class="nf">break_machine</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="sd">"""Break the machine every now and then."""</span>
<span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
<span class="k">yield</span> <span class="bp">self</span><span class="o">.</span><span class="n">env</span><span class="o">.</span><span class="n">timeout</span><span class="p">(</span><span class="n">time_to_failure</span><span class="p">())</span>
<span class="k">if</span> <span class="ow">not</span> <span class="bp">self</span><span class="o">.</span><span class="n">broken</span><span class="p">:</span>
<span class="c1"># Only break the machine if it is currently working.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">process</span><span class="o">.</span><span class="n">interrupt</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">other_jobs</span><span class="p">(</span><span class="n">env</span><span class="p">,</span> <span class="n">repairman</span><span class="p">):</span>
<span class="sd">"""The repairman's other (unimportant) job."""</span>
<span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
<span class="c1"># Start a new job</span>
<span class="n">done_in</span> <span class="o">=</span> <span class="n">JOB_DURATION</span>
<span class="k">while</span> <span class="n">done_in</span><span class="p">:</span>
<span class="c1"># Retry the job until it is done.</span>
<span class="c1"># It's priority is lower than that of machine repairs.</span>
<span class="k">with</span> <span class="n">repairman</span><span class="o">.</span><span class="n">request</span><span class="p">(</span><span class="n">priority</span><span class="o">=</span><span class="mi">2</span><span class="p">)</span> <span class="k">as</span> <span class="n">req</span><span class="p">:</span>
<span class="k">yield</span> <span class="n">req</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">start</span> <span class="o">=</span> <span class="n">env</span><span class="o">.</span><span class="n">now</span>
<span class="k">yield</span> <span class="n">env</span><span class="o">.</span><span class="n">timeout</span><span class="p">(</span><span class="n">done_in</span><span class="p">)</span>
<span class="n">done_in</span> <span class="o">=</span> <span class="mi">0</span>
<span class="k">except</span> <span class="n">simpy</span><span class="o">.</span><span class="n">Interrupt</span><span class="p">:</span>
<span class="n">done_in</span> <span class="o">-=</span> <span class="n">env</span><span class="o">.</span><span class="n">now</span> <span class="o">-</span> <span class="n">start</span>
<span class="c1"># Setup and start the simulation</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'Machine shop'</span><span class="p">)</span>
<span class="n">random</span><span class="o">.</span><span class="n">seed</span><span class="p">(</span><span class="n">RANDOM_SEED</span><span class="p">)</span> <span class="c1"># This helps reproducing the results</span>
<span class="c1"># Create an environment and start the setup process</span>
<span class="n">env</span> <span class="o">=</span> <span class="n">simpy</span><span class="o">.</span><span class="n">Environment</span><span class="p">()</span>
<span class="n">repairman</span> <span class="o">=</span> <span class="n">simpy</span><span class="o">.</span><span class="n">PreemptiveResource</span><span class="p">(</span><span class="n">env</span><span class="p">,</span> <span class="n">capacity</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span>
<span class="n">machines</span> <span class="o">=</span> <span class="p">[</span><span class="n">Machine</span><span class="p">(</span><span class="n">env</span><span class="p">,</span> <span class="s1">'Machine </span><span class="si">%d</span><span class="s1">'</span> <span class="o">%</span> <span class="n">i</span><span class="p">,</span> <span class="n">repairman</span><span class="p">)</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">NUM_MACHINES</span><span class="p">)]</span>
<span class="n">env</span><span class="o">.</span><span class="n">process</span><span class="p">(</span><span class="n">other_jobs</span><span class="p">(</span><span class="n">env</span><span class="p">,</span> <span class="n">repairman</span><span class="p">))</span>
<span class="c1"># Execute!</span>
<span class="n">env</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">until</span><span class="o">=</span><span class="n">SIM_TIME</span><span class="p">)</span>
<span class="c1"># Analyis/results</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'Machine shop results after </span><span class="si">%s</span><span class="s1"> weeks'</span> <span class="o">%</span> <span class="n">WEEKS</span><span class="p">)</span>
<span class="k">for</span> <span class="n">machine</span> <span class="ow">in</span> <span class="n">machines</span><span class="p">:</span>
<span class="nb">print</span><span class="p">(</span><span class="s1">'</span><span class="si">%s</span><span class="s1"> made </span><span class="si">%d</span><span class="s1"> parts.'</span> <span class="o">%</span> <span class="p">(</span><span class="n">machine</span><span class="o">.</span><span class="n">name</span><span class="p">,</span> <span class="n">machine</span><span class="o">.</span><span class="n">parts_made</span><span class="p">))</span>
</pre></div>
</div>
<p>The simulation’s output:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">Machine</span> <span class="n">shop</span>
<span class="n">Machine</span> <span class="n">shop</span> <span class="n">results</span> <span class="n">after</span> <span class="mi">4</span> <span class="n">weeks</span>
<span class="n">Machine</span> <span class="mi">0</span> <span class="n">made</span> <span class="mi">3251</span> <span class="n">parts</span><span class="o">.</span>
<span class="n">Machine</span> <span class="mi">1</span> <span class="n">made</span> <span class="mi">3273</span> <span class="n">parts</span><span class="o">.</span>
<span class="n">Machine</span> <span class="mi">2</span> <span class="n">made</span> <span class="mi">3242</span> <span class="n">parts</span><span class="o">.</span>
<span class="n">Machine</span> <span class="mi">3</span> <span class="n">made</span> <span class="mi">3343</span> <span class="n">parts</span><span class="o">.</span>
<span class="n">Machine</span> <span class="mi">4</span> <span class="n">made</span> <span class="mi">3387</span> <span class="n">parts</span><span class="o">.</span>
<span class="n">Machine</span> <span class="mi">5</span> <span class="n">made</span> <span class="mi">3244</span> <span class="n">parts</span><span class="o">.</span>
<span class="n">Machine</span> <span class="mi">6</span> <span class="n">made</span> <span class="mi">3269</span> <span class="n">parts</span><span class="o">.</span>
<span class="n">Machine</span> <span class="mi">7</span> <span class="n">made</span> <span class="mi">3185</span> <span class="n">parts</span><span class="o">.</span>
<span class="n">Machine</span> <span class="mi">8</span> <span class="n">made</span> <span class="mi">3302</span> <span class="n">parts</span><span class="o">.</span>
<span class="n">Machine</span> <span class="mi">9</span> <span class="n">made</span> <span class="mi">3279</span> <span class="n">parts</span><span class="o">.</span>
</pre></div>
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