Source

File: wp-includes/comment.php

function generic_ping( $post_id = 0 ) {
	$services = get_option( 'ping_sites' );

	$services = explode( "\n", $services );
	foreach ( (array) $services as $service ) {
		$service = trim( $service );
		if ( '' !== $service ) {
			weblog_ping( $service );
		}
	}

	return $post_id;
}