Can two parallel invocations of a static method exists in PHP?

What will happen if same static method is called by two parallel threads? Will it make one thread waiting or can two parallel instances of a static method exists?

Assume function don't use member variables and only use local variables.

Example:

<?php

    public class ClassName{

        public static function doStuff(){
            // Function code goes here
        }
    }

Assume this function is called by GET request to the server. Then if two users send a call to the URL exactly at same time, then what will happen?