def doRead(self):
        """
        The only way a write pipe can become "readable" is at EOF, because the
        child has closed it, and we're using a reactor which doesn't
        distinguish between readable and closed (such as the select reactor).

        Except that's not true on linux < 2.6.11. It has the following
        characteristics: write pipe is completely empty => POLLOUT (writable in
        select), write pipe is not completely empty => POLLIN (readable in
        select), write pipe's reader closed => POLLIN|POLLERR (readable and
        writable in select)

        That's what this funky code is for. If linux was not broken, this
        function could be simply "return CONNECTION_LOST".
        """
        if self.enableReadHack:
            return CONNECTION_LOST
        else:
            self.stopReading()

        The only way a write pipe can become "readable" is at EOF, because the
        child has closed it, and we're using a reactor which doesn't
        distinguish between readable and closed (such as the select reactor).

        Except that's not true on linux < 2.6.11. It has the following
        characteristics: write pipe is completely empty => POLLOUT (writable in
        select), write pipe is not completely empty => POLLIN (readable in
        select), write pipe's reader closed => POLLIN|POLLERR (readable and
        writable in select)

        That's what this funky code is for. If linux was not broken, this
        function could be simply "return CONNECTION_LOST".
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/process.py