Ну и readCache с lockCache

    static protected function readCache($id, $items, $timeout = 500, $wLock = null)
    {
        $ok = false;

        if (@is_file(CT_ROOT."/cache/{$id}.info")) {
            $finfo = fopen(CT_ROOT."/cache/{$id}.info", 'rb');
            flock($finfo, LOCK_SH);
            fseek($finfo, 0, SEEK_SET);

            $data = array('info' => @unserialize(stream_get_contents($finfo)));
            if (is_array($data['info']) && isset($data['info']['timestamp']) && isset($data['info']['version']) && ($data['info']['version'] === CT_VERSION)) {
                if (abs((microtime(true) - $data['info']['timestamp']) * 1000) < $timeout) {
                    # cache is ok, demote write lock early if it exists
                    if ($wLock !== null) self::unlockCache($wLock);
                    
                    # read items now
                    $ok = true;
                    foreach ($items as $item)
                        if (@is_file(CT_ROOT."/cache/{$id}.{$item}")) $data[$item] = @unserialize(file_get_contents(CT_ROOT."/cache/{$id}.{$item}"));
                }
            }

            flock($finfo, LOCK_UN);
            fclose($finfo);
        }
        
        return $ok ? $data : false;
    }

    static public function lockCache($id)
    {
        $fh = fopen(CT_ROOT."/cache/{$id}.lock", 'ab+');
        flock($fh, LOCK_EX);
        return $fh;
    }

    static public function writeCache($id, &$data)
        $data['info'] = array('version' => CT_VERSION, 'timestamp' => microtime(true));

        foreach (array_keys($data) as $key) {
            switch ($key) {
                case 'valid':
                case 'changed':
                $data['info'][$key] = $data[$key];
                unset($data[$key]);
                break;
            }
        }

        $finfo = fopen(CT_ROOT."/cache/{$id}.info", 'ab+');
        flock($finfo, LOCK_EX);
        fseek($finfo, 0, SEEK_SET);
        ftruncate($finfo, 0);
        fwrite($finfo, serialize($data['info']));
        fflush($finfo);
        
        foreach ($data as $key => $val) {
            if ($key == 'info') continue;
            file_put_contents(CT_ROOT."/cache/{$id}.{$key}", serialize($val));
        }
        
        flock($finfo, LOCK_UN);
        fclose($finfo);
    }
    
    static public function unlockCache($fh)
    {
        flock($fh, LOCK_UN);
        fclose($fh);
    }

Нормально работает, коллизии исключаются блокировкой. Можно адаптировать хоть к сайту, хоть к чёрту лысому. Структура кэша в примере правда слегка хитрая, под конкретное приложение.