KernelDestructionSubscriber.php

<?php

namespace Drupal\Core\EventSubscriber;

use Symfony\Component\DependencyInjection\ContainerAwareInterface;
use Symfony\Component\DependencyInjection\ContainerAwareTrait;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\TerminateEvent;
use Symfony\Component\HttpKernel\KernelEvents;

/**
 * Destructs services that are initiated and tagged with "needs_destruction".
 *
 * @see \Drupal\Core\DestructableInterface
 */
class KernelDestructionSubscriber implements EventSubscriberInterface, ContainerAwareInterface {
    use ContainerAwareTrait;
    
    /**
     * Holds an array of service ID's that will require destruction.
     *
     * @var array
     */
    protected $services = [];
    
    /**
     * Registers a service for destruction.
     *
     * Calls to this method are set up in
     * RegisterServicesForDestructionPass::process().
     *
     * @param string $id
     *   Name of the service.
     */
    public function registerService($id) {
        $this->services[] = $id;
    }
    
    /**
     * Invoked by the terminate kernel event.
     *
     * @param \Symfony\Component\HttpKernel\Event\TerminateEvent $event
     *   The event object.
     */
    public function onKernelTerminate(TerminateEvent $event) {
        foreach ($this->services as $id) {
            // Check if the service was initialized during this request, destruction
            // is not necessary if the service was not used.
            if ($this->container
                ->initialized($id)) {
                $service = $this->container
                    ->get($id);
                $service->destruct();
            }
        }
    }
    
    /**
     * Registers the methods in this class that should be listeners.
     *
     * @return array
     *   An array of event listener definitions.
     */
    public static function getSubscribedEvents() {
        $events[KernelEvents::TERMINATE][] = [
            'onKernelTerminate',
            100,
        ];
        return $events;
    }

}