def start(self):
        """Start the app for the start subcommand."""
        # First see if the cluster is already running
        try:
            pid = self.get_pid_from_file()
        except PIDFileError:
            pass
        else:
            if self.check_pid(pid):
                self.log.critical(
                    'Cluster is already running with [pid=%s]. '
                    'use "ipcluster stop" to stop the cluster.' % pid
                )
                # Here I exit with a unusual exit status that other processes
                # can watch for to learn how I existed.
                self.exit(ALREADY_STARTED)
            else:
                self.remove_pid_file()
                

        # Now log and daemonize
        self.log.info(
            'Starting ipcluster with [daemon=%r]' % self.daemonize
        )
        # TODO: Get daemonize working on Windows or as a Windows Server.
        if self.daemonize:
            if os.name=='posix':
                daemonize()

        dc = ioloop.DelayedCallback(self.start_controller, 0, self.loop)
        dc.start()
        dc = ioloop.DelayedCallback(self.start_engines, 1000*self.delay, self.loop)
        dc.start()
        # Now write the new pid file AFTER our new forked pid is active.
        self.write_pid_file()
        try:
            self.loop.start()
        except __HOLE__:
            pass
        except zmq.ZMQError as e:
            if e.errno == errno.EINTR:
                pass
            else:
                raise
        finally:
            self.remove_pid_file()
dataset/ETHPy150Open ipython/ipython-py3k/IPython/parallel/apps/ipclusterapp.py/IPClusterStart.start