[wp-trac] [WordPress Trac] #41098: Some cron scheduling events are ignored

[WordPress Trac]

#41098: Some cron scheduling events are ignored
--------------------------+------------------------
 Reporter:  bor0          |       Owner:
     Type:  defect (bug)  |      Status:  closed
 Priority:  normal        |   Milestone:
Component:  Cron API      |     Version:
 Severity:  normal        |  Resolution:  duplicate
 Keywords:  has-patch     |     Focuses:
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Changes (by ocean90):

 * status:  new => closed
 * version:  4.9 =>
 * milestone:  Awaiting Review =>
 * keywords:  has-patch dev-feedback => has-patch
 * resolution:   => duplicate


Old description:

> The problem appears when two different events are scheduled at the same
> time.
>
> It's a bit hard to reproduce, but if one plugin is continuously
> scheduling events (e.g. recurrent schedule every 5 mins, but they execute
> for 5 mins), another plugin's scheduling events might be completely
> ignored.
>
> I believe this is because there is no lock mechanism in the schedule
> functions where we write to the `cron` option in the database.
>
> What happens in the code is:
>
> Continuous (plugin #1): wp-cron.php has `wp_unschedule_event` in a loop
> (which may overwrite `cron` option in the database)
>
> Random (plugin #2): Call `wp_schedule_event` to update `cron` option, but
> plugin #1 may have overwritten it already.

New description:

 The problem appears when two different events are scheduled at the same
 time.

 It's a bit hard to reproduce, but if one plugin is continuously scheduling
 events (e.g. recurrent schedule every 5 mins, but they execute for 5
 mins), another plugin's scheduling events might be completely ignored.

 I believe this is because there is no lock mechanism in the schedule
 functions where we write to the `cron` option in the database.

 What happens in the code is:

 Continuous (plugin !#1): wp-cron.php has `wp_unschedule_event` in a loop
 (which may overwrite `cron` option in the database)

 Random (plugin !#2): Call `wp_schedule_event` to update `cron` option, but
 plugin !#1 may have overwritten it already.

--

Comment:

 Duplicate of #39924 and #13158.

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Ticket URL: <https://core.trac.wordpress.org/ticket/41098#comment:4>
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