Cron is a daemon
Cron is a daemon that executes commands at specified intervals.
These commands are called "cron jobs".
Cron is available on Unix, Linux, and Mac servers.
Windows servers use a Scheduled Task to execute commands.
The actual "cron job" is a time-triggered action that is usually (and most efficiently) performed by your website's hosting server, but can also be configured by a remote server or even from your desktop.
Code Snippet
function mymodule_cron() {
// Short-running operation example, not using a queue:
// Delete all expired records since the last cron run.
$expires = \Drupal::state()->get('my_module.last_check', 0);
$request_time = \Drupal::time()->getRequestTime();
\Drupal::database()
->delete('my_module_table')
->condition('expires', $expires, '>=')
->execute();
\Drupal::state()->set('my_module.last_check', $request_time);
// Long-running operation example, leveraging a queue:
// Queue news feeds for updates once their refresh interval has elapsed.
$queue = \Drupal::queue('my_module.feeds');
$ids = \Drupal::entityTypeManager()
->getStorage('my_module_feed')
->getFeedIdsToRefresh();
foreach (Feed::loadMultiple($ids) as $feed) {
if ($queue->createItem($feed)) {
// Add timestamp to avoid queueing item more than once.
$feed->setQueuedTime($request_time);
$feed->save();
}
}
$ids = \Drupal::entityQuery('my_module_feed')
->accessCheck(FALSE)
->condition('queued', $request_time - 3600 * 6, '<')
->execute();
if ($ids) {
$feeds = Feed::loadMultiple($ids);
foreach ($feeds as $feed) {
$feed->setQueuedTime(0);
$feed->save();
}
}
}
