Working With WP Cron

As mentioned, WordPress has a pseudo cron mechanism available to WordPress developers for scheduling tasks called WP Cron. WP Cron works using series of functions available for plugin developers to create their own cron style tasks. In theory WordPress makes this easy(ish) using the built in cron API but the reality is that it’s not only confusing and awkward to implement but once you’re complete you have to allow for a bit of latitude on the scheduling.

Take a look at scheduling a task in WordPress. Basically, it works by adding a function to your activation hook, within a plugin, that like the below:

<?php 
register_activation_hook(__FILE__, 'my_activation');
add_action('my_hourly_event', 'do_this_hourly');
 
function my_activation() {
	wp_schedule_event(time(), 'hourly', 'my_hourly_event');
}
 
function do_this_hourly() {
	// do something every hour
}
?>

Pretty simple implementation really though not very “cron” like in syntax. The important part is the call to “wp_schedule_event()” which takes 4 parameters (start date, recurrence, hook and arguments). According to the API manual the function:

Schedules a hook which will be executed by the WordPress actions core on a specific interval, specified by you. The action will trigger when someone visits your WordPress site, if the scheduled time has passed. See the Plugin API for a list of hooks.

The problem I had was that this function only allows for 3 options on recurrence; hourly, twicedaily and daily. I needed my function to run at a specific time. (It was EXTREMELY important that it ran during a specific interval.)

This isn’t to say that it’s not possible to schedule a task for a specific time; it’s just a pain in the ass. You have to write all the logic to determine when to add a new task and removing expired tasks. Ughh. To me the question becomes “Should I write a couple hundred lines of code or just add a single line to my crontab?”.

Crontab baby.