title: Can Luigi handle parallel runs of the same pipeline?
body: <p>Users send us orders. On receipt of an order we run a pipeline which consists of run several tasks. Some tasks take days of computer time.</p>
  
  <pre><code># Example pipeline
  order -&gt; task1 -&gt; task2 -&gt; task3 -&gt; Complete
  </code></pre>
  
  <p>I want to start processing each order as it comes in, so our compute cluster will be processing multiple orders and their associated run of the pipeline simultaneously</p>
  
  <pre><code># Diagram showing each order arriving then being processed over time.
  
  |  order1 -&gt; t1 -&gt; t2 -&gt; t3 -&gt; complete
  |             order2 -&gt; t1 -&gt; t2 -&gt; t3 -&gt; complete
  |                        order3 -&gt; t1 -&gt; t2 -&gt; t3 -&gt; complete
  |                        order4 -&gt; t1 -&gt; t2 -&gt; t3 -&gt; complete
  |                                                order5 -&gt; t1 -&gt; t
  ------------------------------------------------------------------
   time 
  </code></pre>
  
  <p>Can you do this in Luigi? </p>
  
  <p>I don't think that you can as when I implement a test pipeline, then try to start another instance of the test pipeline, while the first is running I get the following output from the second pipeline instance.</p>
  
  <pre><code>Pid(s) set([11004]) already running
  
  Process finished with exit code 0
  </code></pre>