register_shutdown_function vs __destruct

phpではなぜ_destruct関数の後にregister_shutdown_义齿
コードはすべてを説明します.

<?php
class T1
{
    function __construct()
    {
        register_shutdown_function(array(&$this, 'shutdown_func'));
    }
    
    function shutdown_func() {
        $fp = fopen("/tmp/t1.txt", "w+");
        fputs($fp, " 
");
        fclose($fp);
    }
};

$obj = new T1();
while (true) {
    // do nothing
}
 ：
Fatal error: Maximum execution time of 30 seconds exceeded in /home/hanyh/workspace/website/t1.php on line 19
 ：
hanyh@hanyh:~/workspace/git/django-pagination$ more /tmp/t1.txt 
 

<?php
class T2
{
    function __destruct()
    {
        $fp = fopen("/tmp/t2.txt", "w+");
        fputs($fp, " 
");
        fclose($fp);
    }
};

$obj = new T2();
while (true) {
    // do nothing
}
 ：
Fatal error: Maximum execution time of 30 seconds exceeded in /home/hanyh/workspace/website/t2.php on line 13
 ：
hanyh@hanyh:~/workspace/git/django-pagination$ more /tmp/t2.txt
/tmp/t2.txt:  

 ， register_shutdown_function ， 。 ， register_shutdown_function。