The main purpose of the Queue API is to provide a way for us to add items to a queue in order to have them processed at a later time. In charge of processing these items are the queue worker plugins, which can be enlisted either automatically by the Drupal cron, manually (programmatically) by us, or by Drush. We will look at an example of all three.
The central player in this API is the implementation of the QueueInterface, which is the actual queue into which we put items. There are two types of queues Drupal can handle-- reliable and unreliable. The first preserves the order in which the items are processed (first in, first out) and guarantees that each item gets processed at least once. In this chapter, we ...
