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A fresh take on running WordPress's cron system, allowing parallel processing
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README.md

Cron Control

Contributors: automattic, ethitter
Tags: cron, cron control, concurrency, parallel, async
Requires at least: 4.4
Tested up to: 5.0
Requires PHP: 7.0
Stable tag: 2.0
License: GPLv2 or later
License URI: http://www.gnu.org/licenses/gpl-2.0.html

Execute WordPress cron events in parallel, with custom event storage for high-volume cron.

Description

Execute WordPress cron events in parallel, with custom event storage for high-volume cron.

Using REST API endpoints (requires WordPress 4.4+), or a Golang daemon, an event queue is produced and events are triggered.

Installation

  1. Define WP_CRON_CONTROL_SECRET in wp-config.php
  2. Upload the cron-control directory to the /wp-content/mu-plugins/ directory
  3. Create a file at /wp-content/mu-plugins/cron-control.php to load /wp-content/mu-plugins/cron-control/cron-control.php

Frequently Asked Questions

Why is PHP 7 required?

To be able to catch fatal errors triggered by event callbacks, and define arrays in constants (such as for adding "Internal Events"), PHP 7 is necessary.

Adding Internal Events

This should be done sparingly as "Internal Events" bypass certain locks and limits built into the plugin. Overuse will lead to unexpected resource usage, and likely resource exhaustion.

In wp-config.php or a similarly-early and appropriate place, define CRON_CONTROL_ADDITIONAL_INTERNAL_EVENTS as an array of arrays like:

define( 'CRON_CONTROL_ADDITIONAL_INTERNAL_EVENTS', array(
array(
	'schedule' => 'hourly',
	'action'   => 'do_a_thing',
	'callback' => '__return_true',
),
) );

Due to the early loading (to limit additions), the action and callback generally can't directly reference any Core, plugin, or theme code. Since WordPress uses actions to trigger cron, class methods can be referenced, so long as the class name is not dynamically referenced. For example:

define( 'CRON_CONTROL_ADDITIONAL_INTERNAL_EVENTS', array(
array(
	'schedule' => 'hourly',
	'action'   => 'do_a_thing',
	'callback' => array( 'Some_Class', 'some_method' ),
),
) );

Take care to reference the full namespace when appropriate.

Increasing Event Concurrency

In some circumstances, multiple events with the same action can safely run in parallel. This is usually not the case, largely due to Core's alloptions, but sometimes an event is written in a way that we can support concurrent executions.

To allow concurrency for your event, and to specify the level of concurrency, please hook the a8c_cron_control_concurrent_event_whitelist filter as in the following example:

add_filter( 'a8c_cron_control_concurrent_event_whitelist', function( $wh ) {
$wh['my_custom_event'] = 2;

return $wh;
} );

Changelog

2.0

  • Support additional Internal Events
  • Break large cron queues into several caches
  • Introduce Golang runner to execute cron
  • Support concurrency for whitelisted events

1.5

  • Convert from custom post type to custom table with proper indices

1.0

  • Initial release
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