Kill any currently executing managed threads.

        See :meth:`ServiceContainer.spawn_managed_thread`

def _kill_managed_threads(self):
        """ Kill any currently executing managed threads.

        See :meth:`ServiceContainer.spawn_managed_thread`
        """
        num_threads = len(self._managed_threads)

        if num_threads:
            _log.warning('killing %s managed thread(s)', num_threads)
            for gt, identifier in list(self._managed_threads.items()):
                _log.warning('killing managed thread `%s`', identifier)
                gt.kill()