def _set_exception(self):
        """Called by a Job object to tell that an exception occured
        during the processing of the function. The object will become
        ready but not successful. The collector's notify_ready()
        method will be called, but NOT the callback method"""
        assert not self.ready()
        self._data = sys.exc_info()
        self._success = False
        self._event.set()
        if self._collector is not None:
            self._collector.notify_ready(self)
Called by a Job object to tell that an exception occured
        during the processing of the function. The object will become
        ready but not successful. The collector's notify_ready()
        method will be called, but NOT the callback method