Re: gstmm add element to pipeline test

[José Alburquerque <jaalburquerque cox net>]

Murray Cumming wrote:
> On Thu, 2007-12-06 at 12:48 -0500, José Alburquerque wrote:
>   
> >   Also, it seems 
> > the destructor is not called unless the "signal watches" have been 
> > removed first.  Maybe a boolean can tell whether the signal has been 
> > enabled and then not have to call add_signal_watch any more.
> >     
>
> Hmm, then I guess we must force the application developer to call
> remove_watch(). Very unpleasant. I still don't think we understand
> enough about this, but I'll happily apply a patch in the meantime.
>
>   
I know it may be a bit of a quick response, but below is the question I 
posted on the gstreamer-dev list on the gst bus signal watch functions 
and a reply:

-------- Original Message --------
Subject: 	[gst-devel] Question on gst_bus_add/remove_signal_watch functions
Date: 	Thu, 06 Dec 2007 13:44:30 -0500
From: 	José Alburquerque <jaalburquerque cox net>
To: 	gstreamer-devel lists sourceforge net



Hello everyone.  I'm involved in gstreamermm with other developers in 
order to provide C++ bindings for gstreamer.  We're moving along quite 
nicely so far, but some of us will most likely ask a few questions here 
every so often (I hope this is fine :-)).  One such question is related 
to the gst_bus_add/remove_signal_watch[_full] functions (which I'm 
presently working on right now).  As I understand the docs, 
gst_add_signal_watch[_full] can be called several times, but 
remove_signal_watch must be called the same number of times to remove 
the watches.

My question is:  does the message signal get transmitted as many times 
as gst_bus_add_signal_watch() has been called or just once regardless?  
If so, why allow several calls to gst_bus_add_signal_watch().  Also, am 
I correct in assuming that the GstBus is not destroyed unless 
gst_bus_remove_signal_watch() is called the same number of times that 
gst_bus_add_signal_watch[_full]() has been called?

I appreciate answers as this is relevant to the C++ "wrapping" process 
that we are using for the C++ bindings.  Thanks.

Sincerely
Jose

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-------- Original Message --------
Subject: 	Re: [gst-devel] Question on gst_bus_add/remove_signal_watch 
functions
Date: 	Thu, 06 Dec 2007 20:12:44 +0000
From: 	Tim Müller <t i m zen co uk>
To: 	gstreamer-devel lists sourceforge net
References: 	<4758430E 5070609 cox net>



On Thu, 2007-12-06 at 13:44 -0500, José Alburquerque wrote:

> One such question is related
> to the gst_bus_add/remove_signal_watch[_full] functions (which I'm
> presently working on right now). As I understand the docs,
> gst_add_signal_watch[_full] can be called several times, but
> remove_signal_watch must be called the same number of times to remove
> the watches.
>
> My question is: does the message signal get transmitted as many times
> as gst_bus_add_signal_watch() has been called or just once regardless?

The signal gets emitted exactly once per message, regardless of how
often gst_bus_add_signal_watch() has been called.


> If so, why allow several calls to gst_bus_add_signal_watch().

To make it easier for independent pieces of code to watch for the same
signal (they don't need to worry about what's done elsewhere in the
application or in other libraries, but only need to call _add/_remove as
required for their own purposes).


> Also, am I correct in assuming that the GstBus is not destroyed unless
> gst_bus_remove_signal_watch() is called the same number of times that
> gst_bus_add_signal_watch[_full]() has been called?

Yes: gst_bus_add_signal_watch() calls gst_bus_add_watch_full() which
calls gst_bus_create_watch() which takes a reference to the bus, and
that reference is not dropped until the source is removed, which only
happens when _remove_signal_watch() has been called as many times as
_add_signal_watch() has been called before.

Cheers
-Tim



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