MenuRouterRebuildSubscriber.php

<?php

namespace Drupal\Core\EventSubscriber;

use Drupal\Core\Cache\Cache;
use Drupal\Core\Database\ReplicaKillSwitch;
use Drupal\Core\Lock\LockBackendInterface;
use Drupal\Core\Menu\MenuLinkManagerInterface;
use Drupal\Core\Routing\RoutingEvents;
use Symfony\Component\EventDispatcher\Event;
use Drupal\Core\Database\Connection;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 * Rebuilds the default menu links and runs menu-specific code if necessary.
 */
class MenuRouterRebuildSubscriber implements EventSubscriberInterface {
    
    /**
     * @var \Drupal\Core\Lock\LockBackendInterface
     */
    protected $lock;
    
    /**
     * The menu link plugin manager.
     *
     * @var \Drupal\Core\Menu\MenuLinkManagerInterface
     */
    protected $menuLinkManager;
    
    /**
     * The replica kill switch.
     *
     * @var \Drupal\Core\Database\ReplicaKillSwitch
     */
    protected $replicaKillSwitch;
    
    /**
     * The database connection.
     *
     * @var \Drupal\Core\Database\Connection
     */
    protected $connection;
    
    /**
     * Constructs the MenuRouterRebuildSubscriber object.
     *
     * @param \Drupal\Core\Lock\LockBackendInterface $lock
     *   The lock backend.
     * @param \Drupal\Core\Menu\MenuLinkManagerInterface $menu_link_manager
     *   The menu link plugin manager.
     * @param \Drupal\Core\Database\Connection $connection
     *   The database connection.
     * @param \Drupal\Core\Database\ReplicaKillSwitch $replica_kill_switch
     *   The replica kill switch.
     */
    public function __construct(LockBackendInterface $lock, MenuLinkManagerInterface $menu_link_manager, Connection $connection, ReplicaKillSwitch $replica_kill_switch) {
        $this->lock = $lock;
        $this->menuLinkManager = $menu_link_manager;
        $this->connection = $connection;
        $this->replicaKillSwitch = $replica_kill_switch;
    }
    
    /**
     * Rebuilds the menu links and deletes the local_task cache tag.
     *
     * @param \Symfony\Component\EventDispatcher\Event $event
     *   The event object.
     */
    public function onRouterRebuild(Event $event) {
        $this->menuLinksRebuild();
        Cache::invalidateTags([
            'local_task',
        ]);
    }
    
    /**
     * Perform menu-specific rebuilding.
     */
    protected function menuLinksRebuild() {
        if ($this->lock
            ->acquire(__FUNCTION__)) {
            $transaction = $this->connection
                ->startTransaction();
            try {
                // Ensure the menu links are up to date.
                $this->menuLinkManager
                    ->rebuild();
                // Ignore any database replicas temporarily.
                $this->replicaKillSwitch
                    ->trigger();
            } catch (\Exception $e) {
                $transaction->rollBack();
                watchdog_exception('menu', $e);
            }
            $this->lock
                ->release(__FUNCTION__);
        }
        else {
            // Wait for another request that is already doing this work.
            // We choose to block here since otherwise the router item may not
            // be available during routing resulting in a 404.
            $this->lock
                ->wait(__FUNCTION__);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() {
        // Run after CachedRouteRebuildSubscriber.
        $events[RoutingEvents::FINISHED][] = [
            'onRouterRebuild',
            100,
        ];
        return $events;
    }

}