class ExportStorageManager

final class ExportStorageManager implements StorageManagerInterface {
    use StorageCopyTrait;
    
    /**
     * The name used to identify the lock.
     */
    const LOCK_NAME = 'config_storage_export_manager';
    
    /**
     * The active configuration storage.
     *
     * @var \Drupal\Core\Config\StorageInterface
     */
    protected $active;
    
    /**
     * The database storage.
     *
     * @var \Drupal\Core\Config\DatabaseStorage
     */
    protected $storage;
    
    /**
     * The event dispatcher.
     *
     * @var \Symfony\Component\EventDispatcher\EventDispatcherInterface
     */
    protected $eventDispatcher;
    
    /**
     * The used lock backend instance.
     *
     * @var \Drupal\Core\Lock\LockBackendInterface
     */
    protected $lock;
    
    /**
     * ExportStorageManager constructor.
     *
     * @param \Drupal\Core\Config\StorageInterface $active
     *   The active config storage to prime the export storage.
     * @param \Drupal\Core\Database\Connection $connection
     *   The database connection.
     * @param \Symfony\Component\EventDispatcher\EventDispatcherInterface $event_dispatcher
     *   The event dispatcher.
     * @param \Drupal\Core\Lock\LockBackendInterface $lock
     *   The used lock backend instance.
     */
    public function __construct(StorageInterface $active, Connection $connection, EventDispatcherInterface $event_dispatcher, LockBackendInterface $lock) {
        $this->active = $active;
        $this->eventDispatcher = $event_dispatcher;
        $this->lock = $lock;
        // The point of this service is to provide the storage and dispatch the
        // event when needed, so the storage itself can not be a service.
        $this->storage = new DatabaseStorage($connection, 'config_export');
    }
    
    /**
     * {@inheritdoc}
     */
    public function getStorage() {
        // Acquire a lock for the request to assert that the storage does not change
        // when a concurrent request transforms the storage.
        if (!$this->lock
            ->acquire(self::LOCK_NAME)) {
            $this->lock
                ->wait(self::LOCK_NAME);
            if (!$this->lock
                ->acquire(self::LOCK_NAME)) {
                throw new StorageTransformerException("Cannot acquire config export transformer lock.");
            }
        }
        self::replaceStorageContents($this->active, $this->storage);
        $this->eventDispatcher
            ->dispatch(ConfigEvents::STORAGE_TRANSFORM_EXPORT, new StorageTransformEvent($this->storage));
        return new ReadOnlyStorage($this->storage);
    }

}