Action Scheduler

A robust scheduling system for WordPress.

Overview

Action Scheduler uses a WordPress custom post type, creatively named scheduled-action, to store the hook name, arguments and scheduled date for an action that should be triggered at some time in the future.

The scheduler will run every minute by attaching itself as a callback to the 'action_scheduler_run_schedule' hook, which is scheduled using WordPress's built-in WP-Cron system.

When triggered, Action Scheduler will check for posts of the scheduled-action type that have a post_date at or before this point in time i.e. actions scheduled to run now or at sometime in the past.

Batch Processing

If there are actions to be processed, Action Scheduler will stake a unique claim for a batch of 20 actions and begin processing that batch. The PHP process spawned to run the batch will then continue processing batches of 20 actions until it times out or exhausts available memory.

If your site has a large number of actions scheduled to run at the same time, Action Scheduler will process more than one batch at a time. Specifically, when the 'action_scheduler_run_schedule' hook is triggered approximately one minute after the first batch began processing, a new PHP process will stake a new claim to a batch of actions which were not claimed by the previous process. It will then begin to process that batch.

This will continue until all actions are processed using a maximum of 5 concurrent queues.

Housekeeping

Before processing a batch, the scheduler will remove any existing claims on actions which have been sitting in a queue for more than five minutes.

Action Scheduler will also trash any actions which were completed more than a month ago.

If an action runs for more than 5 minutes, Action Scheduler will assume the action has timed out and will mark it as failed. However, if all callbacks attached to the action were to successfully complete sometime after that 5 minute timeout, its status would later be updated to completed.

Record Keeping

Events for each action will be also logged in the comments table.

The events logged by default include when an action:

• is created
• starts
• completes
• fails

Actions can also be grouped together using a custom taxonomy named action-group.

Managing Scheduled Actions

Action Scheduler has a built in administration screen for monitoring, debugging and manually triggering scheduled actions.

To enable the interface:

1. Set WP_DEBUG in your site's wp-config.php file.
2. Go to: Tools > Scheduled Actions.

Among other tasks, from the admin screen you can:

• view the scheduled actions with a specific status, like the all actions which have failed or are in-progress (http://cl.ly/image/3A3C1b1p0702).
• view the log entries (comments) for a specific action to find out why it failed (http://cl.ly/image/3h1E0c23081U).
• search for scheduled actions with a certain hook name, arguement or claim ID (http://cl.ly/image/0V1e1s0A2J3Z).
• sort scheduled actions by hook name, scheduled, start or completed date, claim ID or number of log entries.

API Functions

Action Scheduler API vs. WP-Cron API

The Action Scheduler API functions are designed to mirror the WordPress WP-Cron API functions.

Functions return similar values and accept similar arguments to their WP-Cron counterparts. The notable differences are:

• wc_schedule_single_action() & wc_schedule_recurring_action() will return the post ID of the scheduled action rather than boolean indicating whether the event was scheduled
• wc_schedule_recurring_action() takes an interval in seconds as the recurring interval rather than an arbitrary string
• wc_schedule_single_action() & wc_schedule_recurring_action() can accept a $group parameter to group different actions for the one plugin together.
• the wp_ prefix is substituted with wc_ and the term event is replaced with action

Function Reference / wc_schedule_single_action()

Description

Schedule an action to run one time.

Usage

<?php wc_schedule_single_action( $timestamp, $hook, $args, $group ); ?>

Parameters

• $timestamp (integer)(required) The Unix timestamp representing the date you want the action to run. Default: none.
• $hook (string)(required) Name of the action hook. Default: none.
• $args (array) Arguments to pass to callbacks when the hook triggers. Default: array().
• $group (array) The group to assign this job to. Default: ''.

Return value

(integer) the action's ID in the posts table.

Function Reference / wc_schedule_recurring_action()

Description

Schedule an action to run repeatedly with a specified interval in seconds.

Usage

<?php wc_schedule_recurring_action( $timestamp, $interval_in_seconds, $hook, $args, $group ); ?>

Parameters

• $timestamp (integer)(required) The Unix timestamp representing the date you want the action to run. Default: none.
• $interval_in_seconds (integer)(required) How long to wait between runs. Default: none.
• $hook (string)(required) Name of the action hook. Default: none.
• $args (array) Arguments to pass to callbacks when the hook triggers. Default: array().
• $group (array) The group to assign this job to. Default: ''.

Return value

(integer) the action's ID in the posts table.

Function Reference / wc_schedule_cron_action()

Description

Schedule an action that recurs on a cron-like schedule.

Usage

<?php wc_schedule_cron_action( $timestamp, $schedule, $hook, $args, $group ); ?>

Parameters

• $timestamp (integer)(required) The Unix timestamp representing the date you want the action to run. Default: none.
• $schedule (string)(required) $schedule A cron-link schedule string, see http://en.wikipedia.org/wiki/Cron. Default: none.
• $hook (string)(required) Name of the action hook. Default: none.
• $args (array) Arguments to pass to callbacks when the hook triggers. Default: array().
• $group (array) The group to assign this job to. Default: ''.

Return value

(integer) the action's ID in the posts table.

Function Reference / wc_unschedule_action()

Description

Cancel the next occurrence of a job.

Usage

<?php wc_unschedule_action( $hook, $args, $group ); ?>

Parameters

• $hook (string)(required) Name of the action hook. Default: none.
• $args (array) Arguments to pass to callbacks when the hook triggers. Default: array().
• $group (array) The group to assign this job to. Default: ''.

Return value

(null)

Function Reference / wc_next_scheduled_action()

Description

Returns the next timestamp for a scheduled action.

Usage

<?php wc_next_scheduled_action( $hook, $args, $group ); ?>

Parameters

• $hook (string)(required) Name of the action hook. Default: none.
• $args (array) Arguments to pass to callbacks when the hook triggers. Default: array().
• $group (array) The group to assign this job to. Default: ''.

Return value

(integer|boolean) The timestamp for the next occurrence, or false if nothing was found.

Function Reference / wc_get_scheduled_actions()

Description

Find scheduled actions.

Usage

<?php wc_get_scheduled_actions( $args, $return_format ); ?>

Parameters

• $args (array) Arguments to search and filter results by. Possible arguments, with their default values:

•    'hook' => '' - the name of the action that will be triggered
  

•    'args' => NULL - the args array that will be passed with the action
  

•    'date' => NULL - the scheduled date of the action. Expects a DateTime object, a unix timestamp, or a string that can parsed with strtotime().
  

•    'date_compare' => '<=' - operator for testing "date". accepted values are '!=', '>', '>=', '<', '<=', '='
  

•    'modified' => NULL - the date the action was last updated. Expects a DateTime object, a unix timestamp, or a string that can parsed with strtotime().
  

•    'modified_compare' => '<=' - operator for testing "modified". accepted values are '!=', '>', '>=', '<', '<=', '='
  

•    'group' => '' - the group the action belongs to
  

•    'status' => '' - ActionScheduler_Store::STATUS_COMPLETE or ActionScheduler_Store::STATUS_PENDING
  

•    'claimed' => NULL - TRUE to find claimed actions, FALSE to find unclaimed actions, a string to find a specific claim ID
  

•    'per_page' => 5 - Number of results to return
  

•    'offset' => 0
  

•    'orderby' => 'date' - accepted values are 'hook', 'group', 'modified', or 'date'
  

•    'order' => 'ASC'
  

• $return_format (string) The format in which to return the scheduled actions: 'OBJECT', 'ARRAY_A', or 'ids'. Default: 'OBJECT'.

Return value

(array) Array of the actions matching the criteria specified with $args.

Performance Tuning

By default, Action Scheduler will process a minimum of 1,200 actions per hour. On servers which allow long running PHP processes, this will be significantly higher as processes will be able loop over queues indefinitely.

The batch size and number of concurrent queues that may be processed simultaneously is low by default to ensure the scheduler runs on low powered servers; however, you can configure these settings to increase performance on your site.

Increasing Batch Size

By default, Action Scheduler will claim a batch of 20 actions. This small batch size is to minimise the risk of causing a fatal error due to memory exhaustion.

If you know the callbacks attached to your actions use very little memory, or you've tested the number of actions you can process before memory limits are exceeded, you can increase the batch size using the 'action_scheduler_queue_runner_batch_size' filter.

For example, to increase the batch size to 100, we can use the following function:

<?php
function eg_increase_action_scheduler_batch_size( $batch_size ) {
	return 100;
}
add_filter( 'action_scheduler_queue_runner_batch_size', 'eg_increase_action_scheduler_batch_size' );
?>

Increasing Concurrent Batches

By default, Action Scheduler will run up to 5 concurrent batches of actions. This is to prevent consuming all the available connections or processes on your webserver.

However, your server may allow a large number of connection, for example, because it has a high value for Apache's MaxClients setting or PHP-FPM's pm.max_children setting.

If this is the case, you can use the 'action_scheduler_queue_runner_concurrent_batches' filter to increase the number of conncurrent batches allowed, and therefore speed up processing large numbers of actions scheduled to be processed simultaneously.

For example, to increase the allowed number of concurrent queues to 25, we can use the following code:

<?php
function eg_increase_action_scheduler_concurrent_batches( $concurrent_batches ) {
	return 25;
}
add_filter( 'action_scheduler_queue_runner_concurrent_batches', 'eg_increase_action_scheduler_concurrent_batches' );
?>