How to create a basic Cron job scheduling in WP

WP-Cron Jobs

WP-Cron Jobs
=============
Wp-Cron handles scheduling time-based tasks in WordPress. Several WordPress core features, such as checking for updates and publishing scheduled post, utilize WP-Cron.

WP-Cron works by checking, on every page load, a list of scheduled tasks to see what needs to be run. Any tasks due to run will be called during that page load.

Scheduling errors could occur if you schedule a task for 2:00PM and no page loads occur until 5:00PM.

With WP-Cron, all scheduled tasks are put into a queue and will run at the next opportunity (meaning the next page load). So while you can’t be 100% sure when your task will run, you can be 100% sure that it will run eventually.

WP-Cron is given two arguments: the time for the first task, and an interval (in seconds) after which the task should be repeated. For example, if you schedule a task to begin at 2:00PM with an interval of 300 seconds (five minutes), the task would first run at 2:00PM and then again at 2:05PM, then again at 2:10PM, and so on, every five minutes.

To simplify scheduling tasks, WordPress offers three default intervals and an easy method for adding custom intervals.

The default intervals provided by WordPress are:

hourly
twicedaily
daily
weekly (since WP 5.4)

To add a custom interval, you can create a filter, such as:

add_filter( 'cron_schedules', 'example_add_cron_interval' );
function example_add_cron_interval( $schedules ) { 
    $schedules['five_seconds'] = array(
        'interval' => 5,
        'display'  => esc_html__( 'Every Five Seconds' ), );
    return $schedules;
}

This filter function creates a new interval that will allow us to run a cron task every five seconds.

To scheule a atsk wordpress uses below function

if ( ! wp_next_scheduled( 'bl_cron_hook' ) ) {
    wp_schedule_event( time(), 'five_seconds', 'bl_cron_hook' );
}

$timestamp – The UNIX timestamp of the first time this task should execute
$recurrence – The name of the interval in which the task will recur in seconds
$hook – The name of our custom hook to call

You can add the function to be run on this schedule by using the default wordpress hook functionality.

add_action( 'bl_cron_hook', 'bl_cron_exec' );
function bl_cron_exec(){
	write_log(time());
	write_log('junaid TK');
}

function write_log ( $log )  {
  if ( true === WP_DEBUG ) {
    if ( is_array( $log ) || is_object( $log ) ) {
      error_log( print_r( $log, true ) );
    } else {
      error_log( $log );
    }
  }
}

So the function bl_cron_exec will be executed during each five_seconds intervell.