private function pollExitCodePipe()
    {
        if (! isset($this->pipes[3])) {
            return;
        }

        $r = [$this->pipes[3]];
        $w = $e = null;

        $n = @stream_select($r, $w, $e, 0);

        if (1 !== $n) {
            return;
        }

        $data = fread($r[0], 8192);

        if (strlen($data) > 0) {
            $this->fallbackExitCode = (int) $data;
        }
    }