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

[WordPress Trac]

#57271: Cron unschedule / reschedule event errors
---------------------------+-----------------------------
 Reporter:  domainsupport  |      Owner:  audrasjb
     Type:  defect (bug)   |     Status:  assigned
 Priority:  normal         |  Milestone:  Awaiting Review
Component:  Cron API       |    Version:  6.0
 Severity:  normal         |   Keywords:
  Focuses:                 |
---------------------------+-----------------------------
 Multiple users have reported errors since v6.0 across installs with
 completely different themes and plugins ...

 {{{
 [09-Nov-2022 11:28:28 UTC] Cron unschedule event error for hook: do_pings,
 Error code: could_not_set, Error message: The cron event list could not be
 saved., Data: {“schedule”:false,”args”:[]}

 [09-Nov-2022 18:05:03 UTC] Cron unschedule event error for hook:
 wordfence_processAttackData, Error code: could_not_set, Error message: The
 cron event list could not be saved., Data: {“schedule”:false,”args”:[]}

 [21-Nov-2022 07:53:04 UTC] Cron reschedule event error for hook:
 wf_scan_monitor, Error code: could_not_set, Error message: The cron event
 list could not be saved., Data:
 {“schedule”:”wf_scan_monitor_interval”,”args”:[],”interval”:60}

 [21-Nov-2022 07:53:04 UTC] Cron unschedule event error for hook:
 wf_scan_monitor, Error code: could_not_set, Error message: The cron event
 list could not be saved., Data:
 {“schedule”:”wf_scan_monitor_interval”,”args”:[],”interval”:60}
 }}}

 There are many more examples on the support thread
 https://wordpress.org/support/topic/cron-unschedule-event-error-for-hook/

 I have so far been unable to find a way to manually re-produce this issue
 but this is what I have discovered so far ...

 So this error happens when `wp_unschedule_event()` and
 `wp_reschedule_event()` fails.

 `could_not_set` error is presented by` _set_cron_array()` which is the
 return function for `wp_unschedule_event()` and `wp_schedule_event()`.

 `could_not_set` error is returned by `_set_cron_array()` when the updating
 of the cron table fails with `update_option( 'cron', $cron );`.

 `update_option()` fails when …

 1) The `$option` parameter is empty
 This should never happen
 2) The old option value is the same as the new option value
 This suggests the cron job is running more than once but may not be the
 only reason ... ?
 3) The database insert query `$wpdb->update()` fails
 This is a bit worrying but shouldn’t be the case as surely there should be
 an accompanying database error?

 I think we can rule out (1) seeing as the `$option` parameter is never
 empty.

 We can maybe rule out (2) because from the thread above, this happens on
 high traffic sites as well as low traffic sites and on sites using the
 default wp-cron firing as well as cron fired by the system … ?

 The leaves (3) being the most likely cause of the "bug".

 I have tried to assign to @audrasjb (I hope that's OK to do?) because they
 added the commit on the 20th September that started to highlight the issue
 https://github.com/WordPress/WordPress/commit/84d19848666a81584e0007a6ab7f7ad3c990d71a

 I realise that this is not going to be easy to diagnose until the issue
 can be manually replicated but I think it should be looked into.

 Oliver

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Ticket URL: <https://core.trac.wordpress.org/ticket/57271>
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