How to make php scripts run in parallel?

script1.php

<?php
session_start();
sleep(10);

script2.php

<?php
session_start();

I run script1.php in the browser and immediately after script2.php in another browser window. session_start() in开发者_开发技巧 script2.php can't execute until script1.php is not finished executing.

Why it happened and how to make php scripts run in parallel?

---

Try

<?php
session_start();
session_write_close();
sleep(10);

Related: Thoughts on PHP sessions