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Wrangling WP_Cron - WordCamp Grand Rapids 2014

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Learning to schedule tasks, the WordPress way

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Wrangling WP_Cron - WordCamp Grand Rapids 2014

  1. 1. @cklosowski cklosows Wrangling WP_Cron Scheduling Your Tasks the WordPress Way
  2. 2. Chris Klosowski • Plugin Developer (,, GitHub, • Contributing Developer and Support Tech for Easy Digital Downloads • Hang out with my Wife and Kid @cklosowski cklosows
  3. 3. WP_Cron A tool to replace a tool
  4. 4. What is “Cron” • A time-based job scheduler in Unix-like computer operating systems. • Used to schedule jobs (commands or shell scripts) to run periodically at fixed times, dates, or intervals. • Cleanup, populate data into cache, etc.
  5. 5. WP_Cron The platform-agnostic task scheduler
  6. 6. WP_Cron vs Cron • Works on Windows based systems • Works when you don’t have access to cron • Easily allows access to the WordPress core • “Reliably” available to Theme and Plugin developers
  7. 7. Basic Usage <?php wp_schedule_event( $timestamp, $recurrence, $hook, $args ); Simple Right?
  8. 8. Sort Of Some Caveats
  9. 9. $timestamp • The first time you want this item to run • UNIX Timestamp format • Always in UTC (not localized timezone) • Use time(); as it uses GMT for right now • No Default get_option( 'gmt_offset' );
  10. 10. $recurrence • The name of the schedule value • hourly • twicedaily • daily • Using cron_schedules filter, you can add your own recurrences. • Not a timestamp, but a string that references a timestamp • Number of seconds between occurrences
  11. 11. $hook • Essentially does a do_action() when it runs. You would then attach a function to this hook you’re creating. • Possible issue on some systems where the hook must not contain underscores or uppercase characters. (Have not seen this myself)
  12. 12. $args • Optional array of data to pass through the hook • Great for when doing post or page specific crons • Used later when doing lookups for scheduled crons. • Must be an indexed array (no numeric keys)
  13. 13. // Be Kind, Rewind register_deactivation_hook( __FILE__, 'ck_deactivation' ); function ck_deactivation() { wp_clear_scheduled_hook( 'ck_hourly_event_hook' ); } <?php register_activation_hook( __FILE__, 'ck_activation' ); ! function ck_activation() { wp_schedule_event( time(), 'hourly', 'ck_hourly_event_hook' ); } ! add_action( 'ck_hourly_event_hook', 'ck_do_this_hourly' ); function ck_do_this_hourly() { // do something every hour }
  14. 14. <?php // Situation of single event $args = array( 'post_id' => 42, 'service' => 'twitter' ); wp_schedule_single_event( time(), 'ck_single_event', $args ); ! ! // Clear with same hook and EXACT same args $args2 = array( 'post_id' => 42, 'service' => 'twitter' ); wp_clear_scheduled_hook( 'ck_single_event', $args2 );
  15. 15. Why Not WP_Cron? Not all unicorns and rainbows
  16. 16. Because WP_Cron _______________ • Why WP Cron Sucks • Disabling WP-Cron in WordPress • Understanding WP Cron, and why I don’t use it
 …I could go on…
  17. 17. Low Traffic Sites • WP_Cron is based off traffic • No visits, no cron • Unreliable for time specific tasks
  18. 18. High Traffic Sites • Possibility of many concurrent cron events. • Expensive cron events can cause load issues. • If needing EXACT times, still not 100%
  19. 19. Race Conditions • Identified by the same scheduled task running twice, at the same time. • Due to PHP threads, they aren’t aware of each other
  20. 20. Missed Tasks • They will run. • Scenario • Tasks scheduled 8a and 9a. • No cron run until 9:15a • Both tasks will run at 9:15a • Be aware of this when: • Pushing to Web Services • APIs
  21. 21. How to Wrangle WP_Cron • 3rd party ping service (Pingdom) • Setup an actual cron if available
 • Limit threads with DB or file locks • Know what crons are scheduled, and what they do define('DISABLE_WP_CRON', true);
  22. 22. @cklosowski cklosows Questions? Scheduling Your Tasks the WordPress Way