def _stop_unix(self, errors):"""UNIX implementation of process killing@param errors: error messages. stop() will record messages into this list.@type  errors: [str]"""self.exit_code = self.popen.poll() if self.exit_code is not None:logger.debug("process[%s].stop(): process has already returned %s", self.name, self.exit_code)#print "process[%s].stop(): process has already returned %s"%(self.name, self.exit_code)self.popen = Noneself.stopped = Truereturnpid = self.popen.pidpgid = os.getpgid(pid)logger.info("process[%s]: killing os process with pid[%s] pgid[%s]", self.name, pid, pgid)try:# Start with SIGINT and escalate from there.logger.info("[%s] sending SIGINT to pgid [%s]", self.name, pgid)os.killpg(pgid, signal.SIGINT)logger.info("[%s] sent SIGINT to pgid [%s]", self.name, pgid)timeout_t = time.time() + _TIMEOUT_SIGINTretcode = self.popen.poll()while time.time() < timeout_t and retcode is None:time.sleep(0.1)retcode = self.popen.poll()# Escalate non-responsive processif retcode is None:printerrlog("[%s] escalating to SIGTERM"%self.name)timeout_t = time.time() + _TIMEOUT_SIGTERMos.killpg(pgid, signal.SIGTERM)logger.info("[%s] sent SIGTERM to pgid [%s]"%(self.name, pgid))retcode = self.popen.poll()while time.time() < timeout_t and retcode is None:time.sleep(0.2)logger.debug('poll for retcode')retcode = self.popen.poll()if retcode is None:printerrlog("[%s] escalating to SIGKILL"%self.name)errors.append("process[%s, pid %s]: required SIGKILL. May still be running."%(self.name, pid))try:os.killpg(pgid, signal.SIGKILL)logger.info("[%s] sent SIGKILL to pgid [%s]"%(self.name, pgid))# #2096: don't block on SIGKILL, because this results in more orphaned processes overall#self.popen.wait()#os.wait()logger.info("process[%s]: sent SIGKILL", self.name)except OSError as e:if e.args[0] == 3:printerrlog("no [%s] process with pid [%s]"%(self.name, pid))else:printerrlog("errors shutting down [%s], see log for details"%self.name)logger.error(traceback.format_exc())else:logger.info("process[%s]: SIGTERM killed with return value %s", self.name, retcode)else:logger.info("process[%s]: SIGINT killed with return value %s", self.name, retcode)finally:self.popen = None

参考：http://wiki.ros.org/roslaunch