title: Spider stops after one hour of processing one item
body: <p>I have a scrapy spider running in a (non-free) scrapinghub account that sometimes has to OCR a PDF (via Tesseract) - which depending on the number of units can take quite some time.</p>
  
  <p>What I see in the log is something like this:</p>
  
  <pre><code>2220:   2019-07-07 22:51:50 WARNING [tools.textraction] PDF contains only images - running OCR.
  2221:   2019-07-08 00:00:03 INFO    [scrapy.crawler] Received SIGTERM, shutting down gracefully. Send again to force 
  </code></pre>
  
  <p>The <code>SIGTERM</code> always arrives about one hour after the message saying the OCR has started, so I'm assuming there's a mechanism that kills everything if there's no new request or item for one hour.</p>
  
  <p>How can I hook into that, and prevent the shutting down? Is this an example of <code>signal.spider_idle</code>?</p>