Выглядит сие высокоуровнево вот так

        # first, try from cache
        if (is_array($data = self::readCache(self::$cacheId, $items, self::$cacheTimeout))) return $data; # valid cache
        
        # alas, could not validate cache, do the job retrieving data
        $fh = self::lockCache(self::$cacheId);
        
        # one more verification is needed here due to parallelism
        if (is_array($data = self::readCache(self::$cacheId, $items, self::$cacheTimeout, $fh))) return $data; # cache updated by someone and is valid

        ... update cache here ...

        # write and unlock cache, then return
        self::writeCache(self::$cacheId, $data);
        self::unlockCache($fh);
        return $data