title: How to check Rails app's thread safety for Puma
body: <p>I wish to deploy my Rails app to Heroku using Puma webserver. However, I am not really sure whether all Gems are thread safe. Reading all Gems' source code is not feasible option for us.</p>
  
  <p>Is there a way to automatically check all Gems for thread safety? Or does Puma complain/display specific error log if thread unsafe code were executed/detected?</p>