[wp-trac] [WordPress Trac] #57271: Cron unschedule / reschedule event errors

[WordPress Trac]

#57271: Cron unschedule / reschedule event errors
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 Reporter:  domainsupport               |       Owner:  audrasjb
     Type:  defect (bug)                |      Status:  assigned
 Priority:  normal                      |   Milestone:  Awaiting Review
Component:  Cron API                    |     Version:  6.0
 Severity:  normal                      |  Resolution:
 Keywords:  has-patch needs-unit-tests  |     Focuses:
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Comment (by domainsupport):

 @galbaras We rarely see this error anymore but when we do see it it always
 points to some kind of issue with the database (usually a lack of
 resources, temporary or otherwise) which prevents the cron from being
 saved into the options table.

 It's not a welcome explanation to some but we have yet to find a situation
 where this has not been the route cause.

 We created a plugin to detect cron schedules that have no associated
 actions and find it to be very common that plugins forget to register a
 deactivation hook to clean up their cron schedules. So common that we have
 even found and raised issues with [https://wordpress.org/support/topic/wp-
 cron-event-left-after-deactivation/ WPForms],
 [https://wordpress.org/support/topic/wp-cron-
 monsterinsights_usage_tracking_cron-not-being-removed/ MonsterInsights],
 [https://wordpress.org/support/topic/wp-cron-
 googlesitekit_cron_update_remote_features-not-being-removed/ Site Kit by
 Google] and even [https://wordpress.org/support/topic/wp-cron-
 jetpack_v2_heartbeat-not-being-removed/ Jetpack]!

 Duplicate cron schedule entries are also usually attributed to plugin
 error (or a race condition) which we have also seen fairly regularly. We
 don't know of a way to "rebuild" the cron schedule but our previously
 mentioned plugin uses this to remove empty cron schedules if it is of use
 ...

 {{{#!php
 <?php
                 $empty_event_hooks =
 wordpress_maintenance_get_empty_cron_event_hooks();

                 foreach ($empty_event_hooks as $hook) {

                     wp_clear_scheduled_hook($hook);

                 }

        function wordpress_maintenance_get_empty_cron_event_hooks() {

             $cron_events  = _get_cron_array();
             $empty_event_hooks = array();

             if (is_array($cron_events)) {

                 global $wp_filter;

                 foreach ($cron_events as $cron_event) {

                     foreach ($cron_event as $hook => $value) {

                         if ('wc_admin_unsnooze_admin_notes' !== $hook
 &&!isset($wp_filter[$hook])) {

                             $empty_event_hooks[] = $hook;

                         }

                     }

                                 }

                         }

             return array_unique($empty_event_hooks);

         }
 }}}

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/57271#comment:45>
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