High CPU usage related to 3.12 in dashboard only

[piotrbak]

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Describe the bug
It looks we have kind of loop in dashboard caused by incompatibility with 3rd parties. Notices are displayed in a loop until the timeout/fatal error happens.

To Reproduce
We still don't know how to reproduce it. For now suspected conflicts are:

• Ninja Forms
• WPML
• Extra Product Options for WooCommerce

Screenshots

Additional context
Add any other context about the problem here.

Backlog Grooming (for WP Media dev team use only)

• Reproduce the problem
• Identify the root cause
• Scope a solution
• Estimate the effort

[piotrbak]

Potentially related tickets:
https://secure.helpscout.net/conversation/1990980854/364366?folderId=273761
https://secure.helpscout.net/conversation/1990990089/364369?folderId=273761
https://secure.helpscout.net/conversation/1991065735/364385?folderId=273761
https://secure.helpscout.net/conversation/1990685406/364292?folderId=7043481
https://secure.helpscout.net/conversation/1991045594/364381?folderId=273761

[alfonso100]

Another one:
https://secure.helpscout.net/conversation/1991254565/364418?folderId=273761

[alfonso100]

Another case, is related to Ninja Forms.
Disabling ninja forms, or WP Rocket fixes the issue
After enabling WP Rocket, there is a timeout followed by a 524 error from cloudflare

https://secure.helpscout.net/conversation/1988914598/363935?folderId=2683093

update: the proposed fix worked on this case

[alfonso100]

This can be reproduced by installing WP Rocket 3.12.0.3 and Ninja Forms
https://wordpress.org/plugins/ninja-forms/

https://i.imgur.com/QO960oE.png

[alfonso100]

Another one, related to Ninja Forms:
https://secure.helpscout.net/conversation/1990404557/364233?folderId=273761

[piotrbak]

Problem seems to be related to those specific lines, commenting them out fixes it:

wp-rocket/inc/Engine/Preload/Admin/Subscriber.php

Lines 47 to 48 in c09453b

	'maybe_display_preload_notice',
	'maybe_display_as_missed_tables_notice',

Solution proposed by @Tabrisrp is to change those lines to:

 [ 'maybe_display_preload_notice' ],
 [ 'maybe_display_as_missed_tables_notice' ],

It fixes the problem, we need further investigation why it happens only on a very small minority of users.

[DahmaniAdame]

Related - https://secure.helpscout.net/conversation/1990404062/364232/
Fixed by updating

wp-rocket/inc/Engine/Preload/Admin/Subscriber.php

Lines 47 to 48 in c09453b

	'maybe_display_preload_notice',
	'maybe_display_as_missed_tables_notice',

as provided by the PHP.

[alfonso100]

Related https://secure.helpscout.net/conversation/1991065735/364385?folderId=273766

[engahmeds3ed]

Starting from those two lines:

wp-rocket/inc/Engine/Preload/Admin/Subscriber.php

Lines 46 to 49 in fd8afaf

	'admin_notices' => [
	'maybe_display_preload_notice',
	'maybe_display_as_missed_tables_notice',
	],

So when we add the subscriber in the event manager class here:

wp-rocket/inc/classes/event-management/class-event-manager.php

Line 45 in 0aed8bd

$this->add_subscriber_callback( $subscriber, $hook_name, $parameters );

and will pass the following values

  ["subscriber"] => string(41) "WP_Rocket\Engine\Preload\Admin\Subscriber"

  ["hook_name"] => string(13) "admin_notices"

  ["parameters"] => array (
    0 => 'maybe_display_preload_notice',
    1 => 'maybe_display_as_missed_tables_notice',
  )

Then it'll get into the following condition

wp-rocket/inc/classes/event-management/class-event-manager.php

Line 112 in 0aed8bd

$this->add_callback( $hook_name, [ $subscriber, $parameters[0] ], isset( $parameters[1] ) ? $parameters[1] : 10, isset( $parameters[2] ) ? $parameters[2] : 1 );

and based on that, the values that will be passed to add_callback method are as follows:-

$hook_name => admin_notices

$callback => [subscriber, 'maybe_display_preload_notice']

$priority => 'maybe_display_as_missed_tables_notice'

$accepted_args => default value is 1

Notice that this priority has a string value and this should be number and this is the problem.

the problem is on this line from WP core

https://github.com/WordPress/WordPress/blob/master/wp-includes/class-wp-hook.php#L85

So the question is why with some plugins we see this problem like ninjaforms?
the answer took me a lot of time to know as below:

I logged the admin_notices callbacks from WP core and I found as in the following screenshot

this callback has more than 25500 lines and this is extremely big number
the problem with ksort, it takes a lot of time when the keys are not numbers as in this case
if u want to make sure of what I mentioned, simply change this line to be any number

wp-rocket/inc/Engine/Preload/Admin/Subscriber.php

Line 48 in fd8afaf

'maybe_display_as_missed_tables_notice',

Also as @Mai-Saad mentioned, the issue is happening only with PHP >= 8

I'm going to create a PR for this now.

[alfonso100]

related: https://secure.helpscout.net/conversation/1990990089/364369/