docs: def kill(self, wait=True, sig=None):
          """
          Kill the process if running.
  
          :param bool wait: set to `True` to wait for the process to end,
              or False, to simply proceed after sending signal.
          :param int sig: signal used to kill process run by the executor.
              None by default.
          :returns: itself
          :rtype: SimpleExecutor
          """
          if sig is None:
              sig = self._sig_kill
          if self.running():
              os.killpg(self.process.pid, sig)
              if wait:
                  self.process.wait()
  
          self._kill_all_kids(sig)
          self._clear_process()
          return self