Re: gstmm add element to pipeline test

[José Alburquerque <jaalburquerque cox net>]

Murray Cumming wrote:
> On Wed, 2007-12-05 at 17:57 -0500, José Alburquerque wrote:
>   
> > José Alburquerque wrote: 
> >     
> > > Murray Cumming wrote: 
> > >       
> > > > I think we should do this in C++ much as it is done in C:
> > > > - We should have an add_watch(priority) that just causes the signal to
> > > > be emitted.
> > > > and
> > > > - We should have an add_watch(slot) that provides a sigc::slot that is
> > > > called. We have lots of these set_func(slot)-like functions in gtkmm.
> > > >         
> > > Hi.  I'm trying to implement these GstBus "watch" functions and I
> > > have a quick question.  AFAICT, GstBus has the following "watch"
> > > functions:
> > >
> > > gst_bus_add_watch(GstBus*, GstBusFunc func, gpointer)
> > > gs_bus_add_watch_full(GstBus*, gint priority, GstBusFunc func,
> > > gpointer data, GDestroyNotify notify)
> > > gst_bus_add_signal_watch(GstBus*)
> > > gst_bus_add_signal_watch_full(GstBus*, gint priority)
> > > gst_bus_remove_signal_watch(GstBus*)
> > >
> > > As I understand, the first two will be wrapped using slots while the
> > > last three deal with enabling/disabling the Gst::Bus "message"
> > > signal.  My question is:  When these functions are wrapped, should
> > > similar names be used for the methods (eg.
> > > Gst::Bus::add_signal_watch() for gst_bus_add_signal_watch)?
> > >
> > > -Jose
> > >
> > >
> > >       
> > I was sort of thinking of having a Gst::Bus::enable_message_signal()
> > and a Gst::Bus::disable_message_signal() (for the message signal)
> >     
>
> I do wonder if these can be called more than once, and what
> remove_signal_watch() does if I've called it twice. If they can only be
> called once then enable/disable would be clearer, but I think we need to
> discover more.
>
>   
According to the documentation, add_signal_watch[_full] can be called 
more than once (several times), but remove_signal_watch must be called 
the same number of times.  By testing I found that the following error 
is produced if remove_signal_watch is called "once" too often (in other 
words, it cannot be called unless an add_signal_watch[_full] was called 
before):

(gstreamer-ogg-player:5939): GStreamer-CRITICAL **: Bus bus1 has no 
signal watches attached
> >  and then having methods like Gst::Bus::add_watch() and
> > Gst::Bus::add_watch(priority) for the slots. 
> >     
>
> This seems correct.
>   
-Jose