title: How rails resolve multi-requests at the same time?
body: <p><strong>Prepare for the test:</strong>
  <code>sleep 10</code> in a action</p>
  
  <p><strong>Test:</strong>
  Open two tabs in the browser to visit the action</p>
  
  <p><strong>Result:</strong>
  When the second request is running, the first request finished and began rendering the view, but the view is still blank.
  After the second request finished too, the two requests finished rendering the view at the same time. </p>
  
  <p><strong>Conclusion:</strong>
  Rails is just one single instance. One request can only enter the action after the previous requests finish. But how to explain the response part? Why the multi-requests finish rendering the views at the same time?</p>