How to use the mitogen.core.listen function in mitogen

def notice_stream(self, stream):
        """
        When this parent is responsible for a new directly connected child
        stream, we're also responsible for broadcasting
        :data:`mitogen.core.DEL_ROUTE` upstream when that child disconnects.
        """
        self._routes_by_stream[stream] = set([stream.protocol.remote_id])
        self._propagate_up(mitogen.core.ADD_ROUTE, stream.protocol.remote_id,
                        stream.name)
        mitogen.core.listen(
            obj=stream,
            name='disconnect',
            func=lambda: self._on_stream_disconnect(stream),
        )

def _setup_stdio_stream(self):
        stream = self.stream_factory()
        stream.conn = self
        stream.name = self.options.name or self._get_name()
        stream.accept(self.proc.stdout, self.proc.stdin)

        mitogen.core.listen(stream, 'disconnect', self.on_stdio_disconnect)
        self._router.broker.start_receive(stream)
        return stream

def _setup_master(self):
        """
        Construct a Router, Broker, and mitogen.unix listener
        """
        self.broker = mitogen.master.Broker(install_watcher=False)
        self.router = mitogen.master.Router(
            broker=self.broker,
            max_message_size=MAX_MESSAGE_SIZE,
        )
        _setup_responder(self.router.responder)
        mitogen.core.listen(self.broker, 'shutdown', self._on_broker_shutdown)
        mitogen.core.listen(self.broker, 'exit', self._on_broker_exit)
        self.listener = mitogen.unix.Listener.build_stream(
            router=self.router,
            path=self.path,
            backlog=C.DEFAULT_FORKS,
        )
        self._enable_router_debug()
        self._enable_stack_dumps()

my_pid = os.getpid()
    if _pool is None or my_pid != _pool_pid:
        # Avoid acquiring heavily contended lock if possible.
        _pool_lock.acquire()
        try:
            if _pool_pid != my_pid:
                _pool = Pool(
                    router,
                    services=[],
                    size=size or DEFAULT_POOL_SIZE,
                    overwrite=True,
                    recv=mitogen.core.Dispatcher._service_recv,
                )
                # In case of Broker shutdown crash, Pool can cause 'zombie'
                # processes.
                mitogen.core.listen(router.broker, 'shutdown',
                                    lambda: _pool.stop(join=True))
                _pool_pid = os.getpid()
        finally:
            _pool_lock.release()

    return _pool

def _setup_stderr_stream(self):
        stream = self.stderr_stream_factory()
        stream.conn = self
        stream.name = self.options.name or self._get_name()
        stream.accept(self.proc.stderr, self.proc.stderr)

        mitogen.core.listen(stream, 'disconnect', self.on_stderr_disconnect)
        self._router.broker.start_receive(stream)
        return stream

def _install_timer(self, delay):
        new = self._timer is None
        self._timer = self.broker.timers.schedule(
            when=mitogen.core.now() + delay,
            func=self.reap,
        )
        if new:
            mitogen.core.listen(self.broker, 'shutdown',
                                self._on_broker_shutdown)

`init_child_result` is the result of executing
            :func:`ansible_mitogen.target.init_child` in that context, `msg` is
            an error message and the remaining fields are :data:`None`, or
            `msg` is :data:`None` and the remaining fields are set.
        """
        try:
            method = getattr(self.router, spec['method'])
        except AttributeError:
            raise Error('unsupported method: %(method)s' % spec)

        context = method(via=via, unidirectional=True, **spec['kwargs'])
        if via and spec.get('enable_lru'):
            self._update_lru(context, spec, via)

        # Forget the context when its disconnect event fires.
        mitogen.core.listen(context, 'disconnect',
            lambda: self._on_context_disconnect(context))

        self._send_module_forwards(context)
        init_child_result = context.call(
            ansible_mitogen.target.init_child,
            log_level=LOG.getEffectiveLevel(),
            candidate_temp_dirs=self._get_candidate_temp_dirs(),
        )

        if os.environ.get('MITOGEN_DUMP_THREAD_STACKS'):
            from mitogen import debug
            context.call(debug.dump_to_logger)

        self._key_by_context[context] = key
        self._refs_by_context[context] = 0
        return {

def __init__(self, router):
        self.router = router
        self.router.add_handler(
            func=self._on_debug_msg,
            handle=mitogen.core.DEBUG,
            persist=True,
            policy=mitogen.core.has_parent_authority,
        )
        mitogen.core.listen(router, 'register', self._on_stream_register)
        LOG.debug('Context debugging configured.')