def _doSelectInThread(self, timeout):
        """Run one iteration of the I/O monitor loop.

        This will run all selectables who had input or output readiness
        waiting for them.
        """
        reads = self.reads
        writes = self.writes
        while 1:
            try:
                r, w, ignored = _select(reads.keys(),
                                        writes.keys(),
                                        [], timeout)
                break
            except ValueError:
                # Possibly a file descriptor has gone negative?
                log.err()
                self._preenDescriptorsInThread()
            except TypeError:
                # Something *totally* invalid (object w/o fileno, non-integral
                # result) was passed
                log.err()
                self._preenDescriptorsInThread()
            except (select.error, IOError) as se:
                # select(2) encountered an error
                if se.args[0] in (0, 2):
                    # windows does this if it got an empty list
                    if (not reads) and (not writes):
                        return
                    else:
                        raise
                elif se.args[0] == EINTR:
                    return
                elif se.args[0] == EBADF:
                    self._preenDescriptorsInThread()
                else:
                    # OK, I really don't know what's going on.  Blow up.
                    raise
        self._sendToMain('Notify', r, w)
Run one iteration of the I/O monitor loop.

        This will run all selectables who had input or output readiness
        waiting for them.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/_threadedselect.py