Drupal Hook_cron design pattern

Drupal Hook_cron design pattern

/**
 * Implementation of hook_cron().
 */
function example_cron() {
  static $is_running;
  $time = time();
  
  //Call is_active. IF so, stor in variable.
  if (!$is_running && _example_cron_may_run($time, variable_get('example_alive_last_ran', 0), variable_get('example_refresh_interval', 648000))) {
    $is_running = TRUE;
    example_do_complex_updates();
    $is_running = FALSE;
    variable_set('example_alive_last_ran', $time);
  }
}

/**
 * Determine if we must run another cron run, or if not enough time has passed yet.
 *
 * @param $now
 *   timestamp of now.
 * @param $last_ran
 *   Timestamp of last ran date
 * @param $interval
 *   Seconds to wait before next run.
 *
 * @return
 *   Description of return value
 */
function _example_cron_may_run($now, $last_ran, $interval) {
  //how much time has passed between the last run and now?
  $passed = $now - $last_ran;
  
  //is that passed time larger then the amount of seconds to wait before another run?
  return $passed > $interval ? TRUE : FALSE;
}