Clear cache after a scheduler update is queued

[zaerl]

Fixes: Automattic/wp-calypso#90627
Context: p1715613932876249-slack-C01A60HCGUA

Proposed changes:

• Force a cache clear the first ten seconds after a schedule creation, so that scheduled events at the same second will obtain a fresh cache and not previous value
• jetpack_scheduled_update_updated is run only on successful scheduled event creation

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

• Add this branch to Jetpack Beta
• Quickly add/create/modify a scheduled update. Better when the clock is near second zero (08:00:57 -> 08:01:03, etc.)
• Ensure everything is ok

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[obenland]

@ouikhuan @zaerl I don't know if Scheduled Updates is the best place for this, but after reading through the thread (p1715925157297969-slack-C01A60HCGUA), I do wonder if clearing cron option cache on pre_schedule_event for all schedules would be the most straight forward way of solving this? We should also see if we can limit it to the cron entry only, and if not, know why not.

Based on your testing it looks like updating cron array with stale data is not just a problem with ActionScheduler but with any event that gets scheduled in close timely proximity to one another?

[ouikhuan]

@ouikhuan @zaerl I don't know if Scheduled Updates is the best place for this, but after reading through the thread (p1715925157297969-slack-C01A60HCGUA), I do wonder if clearing cron option cache on pre_schedule_event for all schedules would be the most straight forward way of solving this?

Yeah, I agree. This seems to be a more general problem that happens whenever two schedule events run at the same second, and might be better to place this fix somewhere else.

We should also see if we can limit it to the cron entry only, and if not, know why not.

I think we could try to limit it to cron only, explain here.

Based on your testing it looks like updating cron array with stale data is not just a problem with ActionScheduler but with any event that gets scheduled in close timely proximity to one another?

That's correct. It can also be some other events like jetpack_sync_full_cron too.

[ouikhuan]

@zaerl , I think we'll also need to add the "lock" when we try to delete a schedule, since it might also happens when another schedule event is triggered, what do you think?
Here's a scenario:

1. wp_unschedule_event runs -> the cron get removed.
2. At same second another schedule event triggered ( can be jetpack_sync_full_cron )
3. The cron value gets overwritten again.

[zaerl]

@obenland @ouikhuan

1. Removed the create_scheduled_update/delete_scheduled_update functions. Not needed anymore.
2. Changed the cache cleaning method.
3. delete_item now deletes the cache only once time, so it's not deleted multiple times during the same call.
4. The pre_schedule_event_clear_cron_cache now checks if the event differs from the scheduled updates event.
5. Multiple unit tests were added that counted how many times a transient was added.

create_item()
    wp_schedule_event > pre_schedule_event_clear_cron_cache
update_item()
    delete_item()
        wp_unschedule_event
    create_item()
        wp_schedule_event > pre_schedule_event_clear_cron_cache
delete_item()
    wp_unschedule_event > pre_schedule_event_clear_cron_cache

[ouikhuan]

@obenland where do you think it's the best for us to place this fix? Should we put it on the Scheduled Updates package as an initial and run for a while to make sure we don't bring in any side effects and move it to a more general place later? Or should we move it to a more general place directly? If so, where do you think is better? Jetpack plugin or wpcomsh?

[obenland]

where do you think it's the best for us to place this fix?

Yeah, that's a good question.

With the transient it should probably live in scheduled updates. If we removed that transient, it might make sense to put in wpcomsh with review from others. Ultimately it sounds like a consideration for Core?

[ouikhuan]

With the transient it should probably live in scheduled updates. If we removed that transient, it might make sense to put in wpcomsh with review from others. Ultimately it sounds like a consideration for Core?

Yes, I think we'll need to have transient so it only clears the cache when it has to. And since this is more like a general issue for the schedule event system I think it'll be nice to consider adding this to Core eventually.

[ouikhuan]

Tested several times with other schedule events running at the same second and it looks great. Thanks for handling all the feedback!

PR approved