Using g_singal_emit() in GStreamer

[José Alburquerque-3]

Hi everyone.  I have a question about using g_signal_emit() with
GStreamer.  A user in the gtkmm list posted the following statement (see
the orignal post[1] for full context):

With gstreamer (C) we can used g_signal_emit_by_name to received the
tags. ex:

 for (i = 0; i < n_audio; i++) {
   g_signal_emit_by_name (pipeline, "get-audio-tags", i, &tags);
   ...

[1]
http://mail.gnome.org/archives/gtkmm-list/2009-December/msg00045.html

My question is:

How can we know which signals can be used this way?  Would all these
signals have the G_SIGNAL_ACTION flag from the GSignalFlags[2] set?
Would that be a safe way to determine which signals in GStreamer can be
used this way?  Any docs to point me in the right direction would also
be welcome.  Thanks.

[2]
http://library.gnome.org/devel/gobject/2.22/gobject-Signals.html#GSignalFlags

--
José


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[Sebastian Dröge-7]

Am Dienstag, den 15.12.2009, 11:33 -0500 schrieb José Alburquerque:

> My question is:
>
> How can we know which signals can be used this way?  Would all these
> signals have the G_SIGNAL_ACTION flag from the GSignalFlags[2] set?
> Would that be a safe way to determine which signals in GStreamer can
> be used this way?  Any docs to point me in the right direction would also
> be welcome.  Thanks.

Yes, signals with G_SIGNAL_ACTION are meant to be emitted from outside
the element and are handled inside the element. Signals without that
flag should be connected to by the outside and are emitted from inside
the element. That's the same as for the few action signals in GTK :)

For gstreamermm you probably want to provide convenience methods for
these action signals. The C# bindings have this

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[José Alburquerque-3]

On Tue, 2009-12-15 at 17:54 +0100, Sebastian Dröge wrote:
> Yes, signals with G_SIGNAL_ACTION are meant to be emitted from outside
> the element and are handled inside the element. Signals without that
> flag should be connected to by the outside and are emitted from inside
> the element. That's the same as for the few action signals in GTK :)
>
> For gstreamermm you probably want to provide convenience methods for
> these action signals. The C# bindings have this

Thanks for your reply, it's really appreciated.  Some plug-ins have
"action signals" with no return.  For example, fakesrc's "handoff"
signal (which looks to be registered with the G_SIGNAL_ACTION flag)
returns void.  Others don't have parameters either like queue's
"underrun" signal.

Sorry if it's a simple question, but what would be the purpose of
emitting these signals from the outside as opposed to within the
plug-ins?  Thanks for any answers.

--
José


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[Tim-Philipp Müller-2]

On Thu, 2009-12-17 at 14:40 -0500, José Alburquerque wrote:

Hi,

> Some plug-ins have "action signals" with no return.  For example,
>  fakesrc's "handoff" signal (which looks to be registered with the
>  G_SIGNAL_ACTION flag) returns void.  Others don't have parameters
>  either like queue's "underrun" signal.

Neither of those two is an action signal or registered with
G_SIGNAL_ACTION as far as I can tell.

Which is not to say that there aren't action signals with no return
value, see e.g. multifdsink.


> Sorry if it's a simple question, but what would be the purpose of
> emitting these signals from the outside as opposed to within the
> plug-ins?

As you suspect, emitting those signals from outside those elements
indeed doesn't really make sense.

 Cheers
  -Tim



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[José Alburquerque-3]

On Thu, 2009-12-17 at 19:55 +0000, Tim-Philipp Müller wrote:

> On Thu, 2009-12-17 at 14:40 -0500, José Alburquerque wrote:
>
> Hi,
>
> > Some plug-ins have "action signals" with no return.  For example,
> >  fakesrc's "handoff" signal (which looks to be registered with the
> >  G_SIGNAL_ACTION flag) returns void.  Others don't have parameters
> >  either like queue's "underrun" signal.
>
> Neither of those two is an action signal or registered with
> G_SIGNAL_ACTION as far as I can tell.
>
> Which is not to say that there aren't action signals with no return
> value, see e.g. multifdsink.

Oh yes.  I used the wrong test.  Thanks.

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José



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[Sebastian Dröge-7]

Am Donnerstag, den 17.12.2009, 14:40 -0500 schrieb José Alburquerque:

> On Tue, 2009-12-15 at 17:54 +0100, Sebastian Dröge wrote:
> > Yes, signals with G_SIGNAL_ACTION are meant to be emitted from
> outside
> > the element and are handled inside the element. Signals without that
> > flag should be connected to by the outside and are emitted from
> inside
> > the element. That's the same as for the few action signals in GTK :)
> >
> > For gstreamermm you probably want to provide convenience methods for
> > these action signals. The C# bindings have this
>
> Thanks for your reply, it's really appreciated.  Some plug-ins have
> "action signals" with no return.  For example, fakesrc's "handoff"
> signal (which looks to be registered with the G_SIGNAL_ACTION flag)
> returns void.  Others don't have parameters either like queue's
> "underrun" signal.
>
> Sorry if it's a simple question, but what would be the purpose of
> emitting these signals from the outside as opposed to within the
> plug-ins?  Thanks for any answers.

Think of the action signals like normal methods that you can call
on the instance. OTOH normal signals are "events", things connected
to it will be called when something specific happens.


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[José Alburquerque-3]

On Thu, 2009-12-17 at 22:07 +0100, Sebastian Dröge wrote:
> Think of the action signals like normal methods that you can call
> on the instance. OTOH normal signals are "events", things connected
> to it will be called when something specific happens.

Yes, of course.  Thanks.

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José




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[José Alburquerque-3]

On Thu, 2009-12-17 at 17:44 -0500, José Alburquerque wrote:
> On Thu, 2009-12-17 at 22:07 +0100, Sebastian Dröge wrote:
> > Think of the action signals like normal methods that you can call
> > on the instance. OTOH normal signals are "events", things connected
> > to it will be called when something specific happens.
>
> Yes, of course.  Thanks.

I mean to say that I think I understand.  I wanted to thank you and Tim.
With your help I'm well underway to managing something working.  Thanks
again.

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José



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