Club Drupal

  // Delete expired cache entries.

  // Avoid invoking hook_flush_cashes() on every cron run because some modules

  // use this hook to perform expensive rebuilding operations (which are only

  // designed to happen on full cache clears), rather than just returning a

  // list of cache tables to be cleared.

  $cache_object = cache_get('system_cache_tables');

  if (empty($cache_object)) {

    $core = array('cache', 'cache_path', 'cache_filter', 'cache_page', 'cache_form', 'cache_menu');

    $cache_tables = array_merge(module_invoke_all('flush_caches'), $core);

    cache_set('system_cache_tables', $cache_tables);

  }

  else {

    $cache_tables = $cache_object->data;

  }