docs: 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)