I try to keep reference on all instances of a class. Even, unserialized one.

<?php
class A {
    var $x=1;
    
    function __wakeup(){
        $GLOBALS['ref'] =& $this;
    }
}


function set(){
    //Serialize information
    $a =& new A();
    $a->x=2;
    $data = serialize($a);
    
    //Unserialize
    $b =& unserialize($data); // i try without '&'
    $result= $b === $GLOBALS['ref']; // $result == true;    
    echo "VALUE IN SET: {$b->x} \n"; // Echo 2
}

set();
echo "VALUE OUT SET: {$GLOBALS['ref']->x}\n"; //echo nothing, $GLOBALS['ref'] is now NULL !
?>

I have read all docs, my eyes burns me but i really cannot understand. I look in database too.