My system administrator asked me if CiviCRM is thread safe. He could not really explain what he meant by that but he explained me that civicrm should be thread safe because he wants to use Apache Event module as a webserver.
And I don't really know if CiviCRM is thread safe. I have read this topic https://stackoverflow.com/a/5978844/3853493 and it looks like PHP is the problem but not really an application written in PHP.
The question really is, could we use Apache Event module in conjuction with CiviCRM.