FileDB::begin PHP Method

    function begin($exclusive = true)
    {
        if ($this->txFp !== false) {
            throw new LogicException('a transaction is already active');
        }
        $this->txExclusive = $exclusive;
        if (($this->txFp = @fopen($this->file, 'r+')) === false) {
            if (($this->txFp = @fopen($this->file, 'r')) !== false) {
                $this->readOnly = true;
            }
        }
        if ($this->txFp === false) {
            if (file_exists($this->file)) {
                if (is_dir($this->file)) {
                    throw new RuntimeException($this->file . ' is a directory');
                }
                throw new RuntimeException($this->file . ' is not readable');
            }
            if ($this->skeleton_file) {
                copy($this->skeleton_file, $this->file);
                if ($this->createmode !== false) {
                    chmod($this->file, $this->createmode);
                }
                if (($this->txFp = fopen($this->file, 'r+')) === false) {
                    throw new RuntimeException('fopen(' . var_export($this->file, 1) . ', "r+") failed');
                }
            } else {
                if ($this->mkdirs) {
                    $dir = dirname($this->file);
                    if (!file_exists($dir)) {
                        $mode = $this->createmode | 0111;
                        mkdir($dir, $mode, true);
                        chmod($dir, $mode);
                    }
                }
                if (($this->txFp = fopen($this->file, 'x+')) === false) {
                    throw new RuntimeException('fopen(' . var_export($this->file, 1) . ', "x+") failed');
                } elseif ($this->createmode !== false) {
                    chmod($this->file, $this->createmode);
                }
            }
        }
        if ($this->txExclusive && !flock($this->txFp, LOCK_EX)) {
            fclose($this->txFp);
            throw new RuntimeException('flock(<txFp>, LOCK_EX) failed');
        }
    }