虽然循环不会在条件为假时停止

Question

在以下代码片段中，while循环在条件变为false时不会停止。

public function isCircularDependancy($taskId, $newParentId){
        global $pdoHandlerObject;
        $task = $this->getTaskById($taskId);
        if($newParentId == 0){ // This is root task there is no parent
            return false;
        }

        if($task->parent_id == $newParentId){ // Parent is not changed
            return false;
        }

        $currentParentId = $newParentId;
        while($currentParentId != 0){
            if($currentParentId == $task->id){
                return true;
            }
            $currentParent = $this->getTaskById($currentParentId);
            $currentPatentId = $currentParent->parent_id;
        }
        return false;
    }