def _uninstallHandler(self):
        """
        If a child waker was created and installed, uninstall it now.

        Since this disables reactor functionality and is only called
        when the reactor is stopping, it doesn't provide any directly
        useful functionality, but the cleanup of reactor-related
        process-global state that it does helps in unit tests
        involving multiple reactors and is generally just a nice
        thing.
        """
        # XXX This would probably be an alright place to put all of
        # the cleanup code for all internal readers (here and in the
        # base class, anyway).  See #3063 for that cleanup task.
        if self._childWaker:
            self._childWaker.uninstall()

        If a child waker was created and installed, uninstall it now.

        Since this disables reactor functionality and is only called
        when the reactor is stopping, it doesn't provide any directly
        useful functionality, but the cleanup of reactor-related
        process-global state that it does helps in unit tests
        involving multiple reactors and is generally just a nice
        thing.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/posixbase.py