arrays - PHP: Data loss when pass an object -

i have class array of socket

class {     public $clients = array(); }

and class b extends thread in constructor pass class .

class b extends thread {     private $a;     public function __construct($a)     {         $this->a = $a;     } }

next, if add print_r instruction,

$this->a = $a; print_r($this->a); print_r($a);

i have output $this->a

a object (     [clients] => array     (         [0]=> 0     ) )

this output $a.

a object (     [clients] => array     (         [0]=> resource id #n     ) )

why lose socket data?

i have tried pass &$a in construct.

GCM