WordPress/wp-includes/cron.php

<?php

function wp_schedule_single_event( $timestamp, $hook ) {
	$args = array_slice( func_get_args(), 2 );
	$crons = get_option( 'cron' );
	$crons[$timestamp][$hook] = array( 'schedule' => false, 'args' => $args );
	ksort( $crons );
	update_option( 'cron', $crons );
}

function wp_schedule_event( $timestamp, $recurrence, $hook ) {
	$args = array_slice( func_get_args(), 3 );
	$crons = get_option( 'cron' );
	$schedules = wp_get_schedules();
	if ( !isset( $schedules[$recurrence] ) )
		return false;
	$crons[$timestamp][$hook] = array( 'schedule' => $recurrence, 'args' => $args, 'interval' => $schedules[$recurrence]['interval'] );
	ksort( $crons );
	update_option( 'cron', $crons );
}

function wp_reschedule_event( $timestamp, $recurrence, $hook ) {
	$args = array_slice( func_get_args(), 3 );
	$crons = get_option( 'cron' );
	$schedules = wp_get_schedules();
	$interval = 0;

	// First we try to get it from the schedule
	if ( 0 == $interval )
		$interval = $schedules[$recurrence]['interval'];
	// Now we try to get it from the saved interval in case the schedule disappears
	if ( 0 == $interval )
		$interval = $crons[$timestamp][$hook]['interval'];
	// Now we assume something is wrong and fail to schedule
	if ( 0 == $interval )
		return false;

	while ( $timestamp < time() + 1 )
		$timestamp += $interval;

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

function wp_unschedule_event( $timestamp, $hook ) {
	$crons = get_option( 'cron' );
	unset( $crons[$timestamp][$hook] );
	if ( empty($crons[$timestamp]) )
		unset( $crons[$timestamp] );
	update_option( 'cron', $crons );
}

function wp_clear_scheduled_hook( $hook ) {
	while ( $timestamp = wp_next_scheduled( $hook ) )
		wp_unschedule_event( $timestamp, $hook );
}

function wp_next_scheduled( $hook ) {
	$crons = get_option( 'cron' );
	if ( empty($crons) )
		return false;
	foreach ( $crons as $timestamp => $cron )
		if ( isset( $cron[$hook] ) )
			return $timestamp;
	return false;
}

function spawn_cron() {
	if ( array_shift( array_keys( get_option( 'cron' ) ) ) > time() )
		return;

	$cron_url = get_settings( 'siteurl' ) . '/wp-cron.php';
	$parts = parse_url( $cron_url );

	$argyle = @ fsockopen( $parts['host'], $_SERVER['SERVER_PORT'], $errno, $errstr, 0.01 );
	if ( $argyle )
		fputs( $argyle,
			  "GET {$parts['path']}?check=" . md5(DB_PASS . '187425') . " HTTP/1.0\r\n"
			. "Host: {$_SERVER['HTTP_HOST']}\r\n\r\n"
		);
}

function wp_cron() {
	$crons = get_option( 'cron' );
	if ( !is_array($crons) || array_shift( array_keys( $crons ) ) > time() )
		return;

	$schedules = wp_get_schedules();
	foreach ( $crons as $timestamp => $cronhooks ) {
		if ( $timestamp > time() ) break;
		foreach ( $cronhooks as $hook => $args ) {
			if ( isset($schedules[$hook]['callback']) && !call_user_func( $schedules[$hook]['callback'] ) )
				continue;
			spawn_cron();
			break 2;
		}
	}
}

function wp_get_schedules() {
	$schedules = array(
		'hourly' => array( 'interval' => 3600, 'display' => __('Once Hourly') ),
		'daily' => array( 'interval' => 86400, 'display' => __('Once Daily') ),
	);
	return array_merge( apply_filters( 'cron_schedules', array() ), $schedules );
}

?>