$customSocket = new CustomSocket();
$exampleThread = new ExampleThread($customSocket);

class CustomSocket {
    public $socket;

    public function __construct()
    {
        $this->socket = socket_create(AF_UNIX, SOCK_STREAM, 0);
    }
}

class ExampleThread extends Thread {
    public $localCustomSocket;
    public $localSocket;

    public function __construct(CustomSocket $customSocket)
    {
        var_dump($customSocket);

        $this->localCustomSocket = $customSocket;
        var_dump($this->localCustomSocket);

        $constructorCustomSocket = $customSocket;
        var_dump($constructorCustomSocket);

        $this->localSocket = $customSocket->socket;
        var_dump($this->localSocket);
    }
}

object(CustomSocket)#1 (1) {
  ["socket"]=>
  resource(5) of type (Socket)
}
object(CustomSocket)#3 (1) {
  ["socket"]=>
  resource(5) of type (Socket)
}
object(CustomSocket)#1 (1) {
  ["socket"]=>
  resource(5) of type (Socket)
}
resource(5) of type (Socket)

object(CustomSocket)#1 (1) {
  ["socket"]=>
  resource(5) of type (Socket)
}
object(CustomSocket)#3 (1) {
  ["socket"]=>
  int(0)
}
object(CustomSocket)#1 (1) {
  ["socket"]=>
  resource(5) of type (Socket)
}
resource(5) of type (Socket)