QueueFactory.php

<?php

namespace Drupal\Core\Queue;

use Drupal\Core\Site\Settings;
use Symfony\Component\DependencyInjection\ContainerAwareInterface;
use Symfony\Component\DependencyInjection\ContainerAwareTrait;

/**
 * Defines the queue factory.
 */
class QueueFactory implements ContainerAwareInterface {
    use ContainerAwareTrait;
    
    /**
     * Instantiated queues, keyed by name.
     *
     * @var array
     */
    protected $queues = [];
    
    /**
     * The settings object.
     *
     * @var \Drupal\Core\Site\Settings
     */
    protected $settings;
    
    /**
     * Constructs a queue factory.
     */
    public function __construct(Settings $settings) {
        $this->settings = $settings;
    }
    
    /**
     * Constructs a new queue.
     *
     * @param string $name
     *   The name of the queue to work with.
     * @param bool $reliable
     *   (optional) TRUE if the ordering of items and guaranteeing every item executes at
     *   least once is important, FALSE if scalability is the main concern. Defaults
     *   to FALSE.
     *
     * @return \Drupal\Core\Queue\QueueInterface
     *   A queue implementation for the given name.
     */
    public function get($name, $reliable = FALSE) {
        if (!isset($this->queues[$name])) {
            // If it is a reliable queue, check the specific settings first.
            if ($reliable) {
                $service_name = $this->settings
                    ->get('queue_reliable_service_' . $name);
            }
            // If no reliable queue was defined, check the service and global
            // settings, fall back to queue.database.
            if (empty($service_name)) {
                $service_name = $this->settings
                    ->get('queue_service_' . $name, $this->settings
                    ->get('queue_default', 'queue.database'));
            }
            $this->queues[$name] = $this->container
                ->get($service_name)
                ->get($name);
        }
        return $this->queues[$name];
    }

}