Re: difference between "g_signal_emit and g_object_notify" and how to listen to these signals

[hong sheng <hong022011 gmail com>]

Hi Jirka,

Thank you very much. I got the signal in another program. there is g_signal_emit of signal called "signal-quality" in modemmanager, and this signal is received as SignalQuality in another program. However, I feel it is confusing to make the signal name different in the same program without any definition, except that in the creating of new signal for the object, mapping the order of signal array into the introspection of the xml signals. I think it's not robust and not very clear and may need further improvement.

thanks a lot for many helps.

Xiaohong

On Fri, Oct 29, 2010 at 5:17 AM, Jirka Klimes <jklimes redhat com> wrote:

On Thursday 28 of October 2010 01:30:40 hong sheng wrote:
> Hi Daniel,
>
> Thank you very much. I have some more questions.
>
> If I used g_signal_connect at the same program for g_signal_emit, for
> example, in modemmanager, I can receive that signal because I know the
> right object for the signal to connect.
>
> However, in a different program, how can I get the right GObject to connect
> the signal?
>

You can't use pure Glib signals as inter-process communication (IPC). They are
limited for one process only. For communication between two processes you need
some IPC means, like D-Bus.
Nevertheless, D-Bus signals can be used to "extend" glib signals. Thus
g_signal_emit() will in turn issue "SignalQuality" signal on D-Bus. And this
signal is received by the other process and converted to "local" glib signal.

>
> For example, in the open source modemmanager, there is a function called "
> g_signal_emit (self, signals[SIGNAL_QUALITY], 0, quality)", where object:
> self is a modemclass.  If I write my own applet, how can I set
> "g_signal_connect" with right Object of Modem? I mean how can I get the
> right object pointer of Modem for the signal to be connected?
>
> In addition, I found in the openSource applet, there is a function to
> connect signal"SignalQuality" as follows:
>
>         dbus_g_proxy_add_signal (info->cdma_proxy, "SignalQuality",
> G_TYPE_UINT, G_TYPE_INVALID);
>         dbus_g_proxy_connect_signal (info->cdma_proxy, "SignalQuality",
>                                      G_CALLBACK
> (signal_quality_changed_cb), info, NULL);
>
> But I didn't find a place to emit this signal("SignalQuality") either in
> modemmanager or in the networkmanager. Something missed in modemmanager or
> networkmanager?
>

This is the client part of the whole picture.  dbus_g_proxy_add_signal()
specify the signal we are interested in and dbus_g_proxy_connect_signal()
install the handlers that will be called upon signal reception. So, when
ModemManager emits SIGNAL_QUALITY, "SignalQuality" D-Bus signal is emitted (in
addition to local glib signal). The D-Bus signal is received by the applet and
via dbus-glib converted to local glib signal. This causes
signal_quality_changed_cb() handler to be called.

http://dbus.freedesktop.org/doc/dbus-glib/dbus-glib-DBusGProxy.html#dbus-g-
proxy-add-signal

Jirka