function _lock($mode = LOCK_EX)
    {
        if (stristr(php_uname(), 'Windows 9')) {
            return true;
        }

        if ($mode != LOCK_UN && is_resource($this->lock_fp)) {
            // XXX does not check type of lock (LOCK_SH/LOCK_EX)
            return true;
        }

        if (!$this->_assertStateDir()) {
            if ($mode == LOCK_EX) {
                return $this->raiseError('Registry directory is not writeable by the current user');
            }

            return true;
        }

        $open_mode = 'w';
        // XXX People reported problems with LOCK_SH and 'w'
        if ($mode === LOCK_SH || $mode === LOCK_UN) {
            if (!file_exists($this->lockfile)) {
                touch($this->lockfile);
            }
            $open_mode = 'r';
        }

        if (!is_resource($this->lock_fp)) {
            $this->lock_fp = @fopen($this->lockfile, $open_mode);
        }

        if (!is_resource($this->lock_fp)) {
            $this->lock_fp = null;
            return $this->raiseError("could not create lock file" .
                                     (isset($php_errormsg) ? ": " . $php_errormsg : ""));
        }

        if (!(int)flock($this->lock_fp, $mode)) {
            switch ($mode) {
                case LOCK_SH: $str = 'shared';    break;
                case LOCK_EX: $str = 'exclusive'; break;
                case LOCK_UN: $str = 'unlock';    break;
                default:      $str = 'unknown';   break;
            }

            //is resource at this point, close it on error.
            fclose($this->lock_fp);
            $this->lock_fp = null;
            return $this->raiseError("could not acquire $str lock ($this->lockfile)",
                                     PEAR_REGISTRY_ERROR_LOCK);
        }

        return true;
    }