Issue #2208649 by joachim, er.pushpinderrana: document queue worker callback

Author: jhodgdon-drp

modules/system/system.api.php

@@ -606,8 +606,8 @@ function hook_cron() {
  * @return
  *   An associative array where the key is the queue name and the value is
  *   again an associative array. Possible keys are:
- *   - 'worker callback': The name of the function to call. It will be called
- *     with one argument, the item created via DrupalQueue::createItem().
+ *   - 'worker callback': A PHP callable to call that is an implementation of
+ *     callback_queue_worker().
  *   - 'time': (optional) How much time Drupal should spend on calling this
  *     worker in seconds. Defaults to 15.
  *   - 'skip on cron': (optional) Set to TRUE to avoid being processed during
@@ -643,6 +643,28 @@ function hook_cron_queue_info_alter(&$queues) {
   $queues['aggregator_feeds']['time'] = 90;
 }
 
+/**
+ * Work on a single queue item.
+ *
+ * Callback for hook_queue_info().
+ *
+ * @param $queue_item_data
+ *   The data that was passed to DrupalQueue::createItem() when the item was
+ *   queued.
+ *
+ * @throws \Exception
+ *   The worker callback may throw an exception to indicate there was a problem.
+ *   The cron process will log the exception, and leave the item in the queue to
+ *   be processed again later.
+ *
+ * @see drupal_cron_run()
+ */
+function callback_queue_worker($queue_item_data) {
+  $node = node_load($queue_item_data);
+  $node->title = 'Updated title';
+  $node->save();
+}
+
 /**
  * Allows modules to declare their own Form API element types and specify their
  * default values.