playbin as a child element: deadlock when transitioning from PLAYING/PAUSED to NULL

[Dustin Spicuzza]

On 05/30/2015 07:39 AM, Luis de Bethencourt wrote:
> On 30 May 2015 at 06:14, Dustin Spicuzza <dustin at virtualroadside.com
> <mailto:dustin at virtualroadside.com>> wrote:
>
>     Hey,
>
>     I'm using GStreamer 1.4.5 on Fedora 21 via gst-python.
>
>     I'm embedding playbin elements inside of another pipeline, with
>     the goal
>     to use multiple playbins to play multiple files simultaneously and
>     feed
>     them to the same output via an adder -- that part actually works,
>     and I
>     can play two audio streams at once. So far so good.
>
>     However, after I start the pipeline, I've found that I'm having
>     problems
>     stopping it, and it deadlocks.
>
>     PLAYING -> NULL: I did find that if I set the playbin state to NULL
>     before setting its parent's state to NULL, then it doesn't deadlock.
>     However, this leads me to believe I'm missing something here, as I
>     should only need to set the pipe to NULL and not the playbin too,
>     right?
>
>     PAUSED -> NULL: I don't know how to break this deadlock, I'm sure it's
>     something simple I'm missing. It looks like the thread is blocked on a
>     pad lock (gstpad.c:966 - gst_pad_activate_mode) on the GhostPad I
>     created to connect the playbin to the adder. Using GDB, the owner
>     of the
>     lock is the PulseSink thread, who is waiting for something to
>     happen at
>     gst_base_sink_wait_preroll() -- gstbasesink.c:2151.
>
>     I've posted a very short python implementation that demonstrates the
>     problem with a single playbin at github:
>     https://gist.github.com/virtuald/7592a16d6dee07404438
>
>     Thanks for any assistance!
>
>     Dustin
>
>
> Hello Dustin,
>
> I run your Python code and it works with current GStreamer from git. I
> can't reproduce your deadlock.
>
> Could you provide a debug log? [0]
>
> Also, in your case I think it would be better if you used filesrc and
> decodebin, instead of playbin.
>
> I am not very clear on what is the purpose of the Bin you create. What
> is it for?
>
> Thanks,
> Luis
>
> [0]
> http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/gst-running.html

Thanks for trying this out Luis. That's unfortunate that it works with
the latest git.

playbin has 5000+ lines of time-tested code that binds filesrc/decodebin
together, among other things. Why would I try to duplicate that effort
by creating my own filesrc/decodebin/etc?

The 'pipe' pipeline element is created so that every element can have a
common parent. Gstreamer doesn't seem to like it if I try to connect
elements that don't have common parents.

The 'out1' bin element is created so that I can set the 'audio-sink'
property of the playbin, which connects playbin to the adder via the
proxy GhostPad. It was the easiest way I could see to get output from
the playbin.

The goal is to have multiple playbin elements taking care of
decoding/etc, and hook them all up to the adder and output to a single
stream -- and dynamically add/remove the playbins and vary their volumes
independently.

I've added a log to the original gist via:

GST_DEBUG_NO_COLOR=1 GST_DEBUG=4 GST_DEBUG_FILE=debug.log python test.py

https://gist.github.com/virtuald/7592a16d6dee07404438

Thanks so much!

Dustin
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/gstreamer-devel/attachments/20150530/26fc79ad/attachment-0001.html>