<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def cleanup(self):
 """ Release resources used during shell execution """

        for future in self.futures:
            future.cancel()
        self.executor.shutdown(wait=10)
        if self.ssh.get_transport() != None:
            self.ssh.close()