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Automating your plugin with WP-Cron

The document discusses automating plugins with WP-Cron, explaining the differences between traditional cron jobs and WP-Cron, which executes tasks based on site visits. It provides guidelines on scheduling recurring events, setting up custom schedules, and highlights the pros and cons of using WP-Cron. The conclusion emphasizes WP-Cron's effectiveness for WordPress automation, while cautioning that it may not be suitable for all automation needs.

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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