private static function get_kings()
{
if (self::$kings === null) {
$cache = StudipCacheFactory::getCache();
# read cache (unserializing a cache miss - FALSE - does not matter)
$kings = unserialize($cache->read(self::CACHE_KEY));
# cache miss, retrieve from database
if ($kings === FALSE) {
$kings = self::get_kings_uncached();
# write to cache with an expiry time of 24 hours
$cache->write(self::CACHE_KEY, serialize($kings), 86400);
}
self::$kings = $kings;
}
return self::$kings;
}
