How to pass Request to a DoctrineListener

MyListener.php

<?php

namespace AcmeDemo\MyBundle\Listener;

use Doctrine\ORM\Event\OnFlushEventArgs;
use Symfony\Component\HttpFoundation\Request;

class MyListener
{
    /**
     * @var \Symfony\Component\HttpFoundation\Session
     */
    private $session;

    public function __construct(Request $request)
    {
        $this->session = $request->getSession();
    }

    public function onFlush(OnFlushEventArgs $eventArgs)
    {

        /** @var $entityManager \Doctrine\ORM\EntityManager */
        $entityManager = $eventArgs->getEntityManager();

        /** @var $unitOfWork \Doctrine\ORM\UnitOfWork */
        $unitOfWork = $entityManager->getUnitofWork();

        // do stuff to the new entities
        foreach ($unitOfWork->getScheduledEntityInsertions() as $entity) {
            if ($entity instanceof Visitor) {
                $variation = $entityManager->getReference('AcmeDemoMyBundle:Variation', $this->session->get('variation')->getId());
                $variation->incrementVisitorCount();
                
                // ... add variation to unit of work to be persisted / flushed
            }
        }
    }
}

services.yml

services:
    mylistener.listener:
        class: AcmeDemo\MyBundle\Listener\MyListener
        scope: request
        arguments: [@request]
        tags:
            - { name: doctrine.event_listener, event: onFlush,  method: onFlush }