title: A php file using sleep() function cannot run simultaneously
body: <p>I'm newbie in php. I'm now have a problem with sleep function, that is, I have a simple sleep.php file like this: 
  <code>&lt;?php
  echo date('Y-m-d H:i:s');
  sleep(5);
  ?&gt;</code></p>
  
  <p>When I hit this file simultaneously in 2 tabs, the first one executes and give this result: 2013-05-04 10:06:24<br>
  but the second one has to wait for the first one executes completely then give the result: 2013-05-04 10:06:29</p>
  
  <p>My question is why do they cannot execute simultaneously at the same time? Is this php action or because of web service or something else. I'm running nginx 1.3.0</p>
  
  <p>Thanks in advance!</p>