Automating your plugin with WP-Cron

Automating Your Plugins With WP-Cron WordCamp Savannah 2010 Dan Cannon @ NicasioDesign http://nicasiodesign.com

Overview
Background and General Info
Code
Plugin File/Demo
Pros & Cons
Practical Uses
Conclusion
Demo Plugin Used in Presentation:
http://bit.ly/bhZyYU

What is a Traditional Cron Job?
“ Cron is a time-based job scheduler in Unix-like computer operating systems. The name cron comes from the word ‘chronos’, Greek for ‘time’. Cron enables users to schedule jobs … to run periodically at certain times or dates. It is commonly used to automate system maintenance or administration, though its general-purpose nature means that it can be used for other purposes…” - Wikipedia (http://en.wikipedia.org/wiki/Cron_job)

What is WP-Cron?
WP-Cron is a pseudo Cron Job
Executed after a certain time, the next time someone visits the site.
Controlled by a group of WordPress functions
Usually implemented in plugins that need to automate a task

WP-Cron vs Traditional Cron
Why use WP-Cron
Setting up traditional cron jobs can vary depending on server OS and settings
Don’t want to tell plugin users they have to setup a cron job to use your plugin
Most won’t even know where to begin

Schedule a Recurring Event
wp_schedule_event($timestamp,$recurrence,$hook,$args)
$timestamp = UNIX timestamp we want to start the job
Usually PHP time() function
$recurrence = hourly, twicedaily, daily
We can add our own schedules (covered later)
$hook = the hook we want to be called on execution
$args = arguments to pass to the hook’s function (optional)

Schedule a Recurring Event (cont.) Schedule Event on Plugin Activation http://codex.wordpress.org/Function_Reference/wp_schedule_event http://codex.wordpress.org/Function_Reference/register_activation_hook

Schedule a Recurring Event (cont.) The actual function we want to run once an hour http://codex.wordpress.org/Function_Reference/wp_insert_post

Schedule a Recurring Event (cont.)
We need to clear our job when the plugin is deactivated
http://codex.wordpress.org/Function_Reference/wp_clear_scheduled_hook http://codex.wordpress.org/Function_Reference/register_deactivation_hook

Cron Schedule
Three Default recurrence values as of WordPress 3.0.1
Once Hourly
Twice Daily
Once Daily
Output of wp_get_schedules()
http://codex.wordpress.org/Function_Reference/wp_get_schedules

Cron Schedule
Add Our Own Schedules
http://codex.wordpress.org/Plugin_API/Filter_Reference/cron_schedules

Use Custom Schedules

Schedule a Single Event
wp_schedule_single_event( $timestamp, $hook, $args )
$timestamp – UNIX timestamp that you want event to run at
$hook – hook that should be called at proper time
$args – (optional) arguments to pass to the hook’s function
http://codex.wordpress.org/Function_Reference/wp_schedule_single_event

Schedule a Single Event
Similar Syntax/Implementation to recurring events

Avoid Redundant Jobs
Use wp_next_scheduled to see if an event is already scheduled to avoid setting up redundant jobs
Useful for events declared in theme functions file, or events scheduled on the fly
Will return timestamp for next event for a given hook
http://codex.wordpress.org/Function_Reference/wp_next_scheduled

Pros
WordPress Standard
Will still work after upgrades (in theory)
System Independent
Works on all flavors of Linux and Windows
Makes life easy for end users
No messy system or hosting settings to change

Cons
Not Precise
Will run after a certain point, the next time someone visits the site
No Traffic = No Job
If no one visits your site, your job won’t run
Tip: Use a service like WebCron.org to make sure important jobs get executed

Cons (cont.)
Can be hard on server resources
Multiple jobs running often can be hard on your server resources.
Can affect your site in different ways depending on your hosting provider/server
Can be Problematic with Caching
If your site uses caching then WP-Cron jobs will only run on page loads where your cache is rebuilt for that page
Could mean fewer executions for your jobs depending on frequency and traffic volume.

Practical Uses
API Integration
Help cut down external API calls by storing API data periodically
Database and Site Maintenance
Mailing Lists and Reminders
Break up large lists over a long period of time
Content Aggregation
Any Others?

Conclusion
WP-Cron functions provide powerful automation for WordPress plugins, but may not be right for every situation requiring automation.
Dan Cannon
@ NicasioDesign
http://nicasiodesign.com

Automating your plugin with WP-Cron

by Dan Cannon on Aug 21, 2010

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Automating your plugin with WP-Cron — Presentation Transcript

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