ControllerA calls method from ControllerB

[eluser]tokyotech[/eluser]
How do I get one controller to call a method from another controller? Is it considered bad practice if I have to resort to doing this? Let me explain why I need to do this. I have this ControllerB which has a methodB() which I'd like to use both from JS land and PHP land.

Code:

class ControllerB extends Controller {
   public function methodB() {
      session_start();
      $_SESSION['sessionB'] = 'i am set';
   }
}

JS can call it through AJAX:

Code:

[removed]
   new Ajax.Request(
      'index.php/controllerB/methodB'
   );
[removed]

But it's also useful in PHP land for controllerA to call controllerB/methodB:

Code:

class ControllerA extends Controller {
   public function methodA() {
      //psuedocode which I don't know how to do:
      $this->load->controller('controllerB');
      $this->controllerB->methodB();
   }
}