title: PHP - Session object destruction failed
body: <p>I'm facing a strange problem on Symfony: basically sometimes, without any apparent reason, the user is unable to load web pages until I restart php-fpm or until he changes its <code>PHPSESSID</code> loading a new session. Anyway his session is still working properly after fpm is restarted.</p>
  
  <p>At the same time, I got 2 warnings from PHP:</p>
  
  <blockquote>
    <p>PHP Warning:  session_start(): Session object destruction failed in
    /home/unix/releases/1/vendor/symfony/symfony/src/Symfony/Component/HttpFoundation/Session/Storage/NativeSessionStorage.php
    on line 145</p>
    
    <p>PHP Warning:  session_start(): Failed to decode session object.
    Session has been destroyed in
    /home/unix/releases/1/vendor/symfony/symfony/src/Symfony/Component/HttpFoundation/Session/Storage/NativeSessionStorage.php
    on line 145</p>
  </blockquote>
  
  <p>Consider that we are talking about a private website used maximum from 2-3 users concurrently, but it might also happen if just 1 user is navigating on it.</p>
  
  <p>Current setup is</p>
  
  <ul>
  <li>Debian 9.4 stretch 4.14.0-0.bpo.3-amd64</li>
  <li>php-fpm 7.1.15</li>
  <li>Symfony 3.4.4</li>
  </ul>
  
  <p>I'm able to reproduce the issue using <a href="https://httpd.apache.org/docs/2.4/programs/ab.html" rel="nofollow noreferrer">apache ab</a> calling different URLs concurrently using the same session id. Of course after <em>N</em> requests I got timeout:</p>
  
  <pre><code>Completed 100 requests
  Completed 200 requests
  Completed 300 requests
  Completed 400 requests
  Completed 500 requests
  Completed 600 requests
  Completed 700 requests
  Completed 800 requests
  apr_pollset_poll: The timeout specified has expired (70007)
  Total of 872 requests completed
  </code></pre>
  
  <p>Now I'm trying to check php configuration but actually is quite "normal" without special settings so I don't know what should I try or check. Any thoughts?</p>