onAfterCartUpdate infinite loop

public function onAfterCartUpdate(&$cartClass,&$cart,$product_id,$quantity,$add,$type,$resetCartWhenUpdate,$force){
		//die(print_r($product_id));
		
		//if( $product_id != '17962' ){ Does not work because $product_id is an Array, and the id is either the "real" product id, or the id from the table "hikashop_cart_product", which I do not know
			
			$c = $cartClass->loadFullCart();
			if( count($c->products) ){

				$sum = 0;			
				foreach($c->products as $i => $product){
					if( !empty($product->length) ){ // if product has custom field "length"
						$sum += $product->cart_product_quantity - 1; // that "- 1" is willed...
					}
				}
				
				$cartClass->update('17962', $sum); // infinite loop
				
			}
		//}
	}