wp_unschedule_hook() │ WP 4.9.0

Unschedules all events attached to the hook.

Can be useful for plugins when deactivating to clean up the cron queue.

Warning: This function may return boolean false, but may also return a non-boolean value which evaluates to false. For information about casting to booleans see the PHP documentation. Use the === operator for testing the return value of this function.

Uses: _set_cron_array()
Hooks from the function

Return

Int|false|WP_Error. On success an integer indicating number of events unscheduled (0 indicates no events were registered on the hook), false or WP_Error if unscheduling fails.

Usage

wp_unschedule_hook( $hook, $wp_error );
$hook(string) (required)
Action hook, the execution of which will be unscheduled.
$wp_error(true|false)
Whether to return a WP_Error on failure.
Default: false

Examples

0

#1 Remove (Cancel) all Cron events of the CRON hook 

wp_unschedule_hook( 'my_hourly_event' );
0

#2 Cancel all cron events when the plugin is deactivated 

// when deactivating the plugin, cancel the previously created task
register_deactivation_hook( __FILE__, 'my_deactivation');

// add a task when the plugin is activated
register_activation_hook( __FILE__, 'my_activation' );

function my_deactivation() {
	wp_unschedule_hook( 'my_hourly_event' );
}

function my_activation() {

	// Delete all the same cron tasks, just in case, to add new ones from a "clean slate".
	// This may be necessary if the same task was added incorrectly before 
	// (without checking if it already exists)
	wp_unschedule_hook( 'my_hourly_event' );

	// add a new cron task
	wp_schedule_event( time(), 'hourly', 'my_hourly_event');
}

Changelog

Since 4.9.0 Introduced.
Since 5.1.0 Return value added to indicate success or failure.
Since 5.7.0 The $wp_error parameter was added.

wp_unschedule_hook() code WP 6.6.2

wp-includes/cron.php 
function wp_unschedule_hook( $hook, $wp_error = false ) {
	/**
	 * Filter to override clearing all events attached to the hook.
	 *
	 * Returning a non-null value will short-circuit the normal unscheduling
	 * process, causing the function to return the filtered value instead.
	 *
	 * For plugins replacing wp-cron, return the number of events successfully
	 * unscheduled (zero if no events were registered with the hook). If unscheduling
	 * one or more events fails then return either a WP_Error object or false depending
	 * on the value of the `$wp_error` parameter.
	 *
	 * @since 5.1.0
	 * @since 5.7.0 The `$wp_error` parameter was added, and a `WP_Error` object can now be returned.
	 *
	 * @param null|int|false|WP_Error $pre      Value to return instead. Default null to continue unscheduling the hook.
	 * @param string                  $hook     Action hook, the execution of which will be unscheduled.
	 * @param bool                    $wp_error Whether to return a WP_Error on failure.
	 */
	$pre = apply_filters( 'pre_unschedule_hook', null, $hook, $wp_error );

	if ( null !== $pre ) {
		if ( $wp_error && false === $pre ) {
			return new WP_Error(
				'pre_unschedule_hook_false',
				__( 'A plugin prevented the hook from being cleared.' )
			);
		}

		if ( ! $wp_error && is_wp_error( $pre ) ) {
			return false;
		}

		return $pre;
	}

	$crons = _get_cron_array();
	if ( empty( $crons ) ) {
		return 0;
	}

	$results = array();

	foreach ( $crons as $timestamp => $args ) {
		if ( ! empty( $crons[ $timestamp ][ $hook ] ) ) {
			$results[] = count( $crons[ $timestamp ][ $hook ] );
		}

		unset( $crons[ $timestamp ][ $hook ] );

		if ( empty( $crons[ $timestamp ] ) ) {
			unset( $crons[ $timestamp ] );
		}
	}

	/*
	 * If the results are empty (zero events to unschedule), no attempt
	 * to update the cron array is required.
	 */
	if ( empty( $results ) ) {
		return 0;
	}

	$set = _set_cron_array( $crons, $wp_error );

	if ( true === $set ) {
		return array_sum( $results );
	}

	return $set;
}

cron (schedule)