private function isPipe(): bool
    {
        if ($this->isPipe === null) {
            $this->isPipe = false;

            if (isset($this->stream)) {
                $mode         = \fstat($this->stream)['mode'];
                $this->isPipe = ($mode & self::FSTAT_MODE_S_IFIFO) !== 0;
            }
        }

        return $this->isPipe;
    }