Scheduling subscriber notifications

Sending notifications is a common task in any web application. In this scenario, we have subscribers who want to receive e-mail updates about developer activities. In Chapter 8, Enhancing the Power of Open Source Libraries and Plugins, we created a simple e-mail notification system on post publish. Notifying subscribers on post publish can become impossible in a situation where you have a large number of subscribers. Therefore, we are going to take a look at the scheduling features of WordPress for automating the notification-sending process.

As a developer, you might be familiar with cron, which executes certain tasks in a time-based manner. WordPress scheduling functions offer the same functionalities with lesser flexibility. Let's see how to schedule subscriber notifications for predefined time intervals using the wp_schedule_event function of WordPress:

wp_schedule_event($timestamp, $recurrence, $hook, $args);

The preceding code illustrates the basic...