Doctrine\OXM\Storage\FileSystemStorage::lock PHP Method

    private function lock($filename, $handle)
    {
        if (!isset($this->fileLocks[$filename])) {
            $success = flock($handle, LOCK_EX);
            if ($success) {
                $this->fileLocks[$filename] = $handle;
            }
            return $success;
        }
    }