ALTERNATE_WP_CRON runs wp_cron() too early

[r-a-y]

See #19818 for full details.

Then, read my comment in that ticket. Was advised to create a new ticket.

We need to run 'wp_cron' later than the default priority of 10 to allow plugins that run on this hook to properly initialize.

In the patch, I've bumped the priority to 99. Let me know what you think.

[r-a-y]

Thanks for correcting the ticket title, Sergey!

And thanks for the feedback from the previous ticket.

[prettyboymp]

To match where it runs with a normal cron, the hook should probably be changed to 'wp_loaded'.

[peterwilsoncc]

This is worth some investigation so I'm reopening this and putting it down for a future release. The Cron component has a bit of a backlog, so I won't give a timeframe for now as it would set a false expectation.

[peterwilsoncc]

#37542 was marked as a duplicate.

[peterwilsoncc]

From #37542:

This can be an issue for sites registering custom taxonomies. Taxos can not be registered prior to the init hook but using the default priority causes the taxo to be registered after the cron hook fires when using alternative cron.

[peterwilsoncc]

Moving this on to the 5.7 milestone for an early look.

• I understand this will have a side-effect of fixing #20537 too
• It's a backward compatibility break to simply move the action from 10 to a higher number. It's possible to maintain it by using wp_cron to register an action to run later on init. Possible but ugly.

[johnbillion]

I'm happy to help out with any of these cron tickets Peter, just shout.

[peterwilsoncc]

Doing some research to determine backward compatibility issues.

​https://wpdirectory.net/search/01ESJ720E4PB7VBTX7YMYX9JTB

• ten plugins run remove_action( 'init', 'wp_cron' )
• the three most popular have 300K+, 40K+, and 20K+ installs

I do like @prettyboymp's suggestion above of moving the wp_loaded function to match the execution point in which alternative cron runs to the standard wp-cron. It would probably need to run late on that too (ie, priority 20 or higher).

---

@johnbillion I think it's safest to go with some ugly code to maintain backward compatibility. What are your thoughts on the following?

wp_cron() renamed to _wp_cron(), wp_cron_loaded() or similar.

wp_cron() continues to run on init, 10 and then looks something like this:

function wp_cron() {
  if ( did_action( 'wp_loaded' ) {
    return _wp_cron();
  }

  add_action( 'wp_loaded', '_wp_cron', 20 );
}

https://core.trac.wordpress.org/ticket/24160

[johnbillion]

For anyone like me who is trying to wrap their head around what exactly the problem is:

• When wp-cron.php is accessed with a direct POST request, either as a result of spawn_cron() or as a result of a real server cron job requesting it, wp-load.php is included and then any pending cron events are iterated and run. This means actions such as init and wp_loaded have finished executing by the point where the cron events are run.
• With ALTERNATE_WP_CRON in use, the wp_cron function that's hooked into init does an include_once( 'wp-cron.php' ) which then iterates and runs pending cron events after flushing a redirect header to the client.

This means with ALTERNATE_WP_CRON in use, cron events run within the init hook on priority 10. Without it in use, they run after the wp_loaded action has fired.

To bring these two situations closer, the wp_cron function should be hooked into wp_loaded with a late priority, as per Peter's comment and PR above.

[johnbillion]

I agree with the approach in ​https://github.com/WordPress/wordpress-develop/pull/842

[peterwilsoncc]

In 50135:

Cron API: Run alternative wp-cron later, do not run on archived blogs.

Runs cron jobs later on sites using alternative cron, ie the ALTERNATE_WP_CRON constant is true, to more closely match when standard cron jobs are run. Jobs now run on the wp_loaded hook at priority 20. Prior to this change they would run on the init hook. This ensures custom post types and taxonomies are registered prior to the jobs running.

This change also prevents alternative wp-cron from running on archived or suspended multisite blogs as these are shut down prior to the wp_loaded hook from running.

Moves the existing functionality of wp_cron() in to a new private function _wp_cron().

Props flixos90, jeremyfelt, johnbillion, jrf, kurtpayne, nacin, peterwilsoncc, prettyboymp, r-a-y, ryan, stevenkword, swissspidy.
Fixes #20537, #24160.