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 = None            self.stopped = True            return        pid = self.popen.pid        pgid = 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_SIGINT            retcode = self.popen.poll()            while time.time() < timeout_t and retcode is None:                time.sleep(0.1)                retcode = self.popen.poll()            # Escalate non-responsive process            if retcode is None:                printerrlog("[%s] escalating to SIGTERM"%self.name)                timeout_t = time.time() + _TIMEOUT_SIGTERM                os.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

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