public static function check_out() {
    // See if the state is locked.
    if ( true === get_transient( 'jetpack-sitemap-state-lock' ) ) {
      // If it is, return false.
      return false;
    } else {
      // Otherwise, lock the state for 15 minutes and then return it.
      set_transient( 'jetpack-sitemap-state-lock', true, JP_SITEMAP_LOCK_INTERVAL );
      return get_option( 'jetpack-sitemap-state', self::initial() );
    }
  }