Stall when reading only a portion of an MP3 file

Dinesh Iyer dsi.maillist at gmail.com
Wed Jan 10 15:14:36 UTC 2018 

Hi team
I am developing an application that uses Gstreamer for reading audio files.
I am using a playbin connected to an appsink to do the reading. I am
getting a stall only for MP3 files when I attempt to stop the pipeline i.e.
move the state from PLAYING->NULL before I have read until the end of
file.The stall happens in the call to:

gst_element_set_state(element, GST_STATE_NULL);

The traces for the relevant threads are below:
Thread 49 (Thread 0x7f9c2b2a3700 (LWP 59340)):
#0  syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
#1  0x00007f9c87b1d24f in g_cond_wait () from
/lib/x86_64-linux-gnu/libglib-2.0.so.0
#2  0x00007f9c2e25cd66 in gst_app_sink_event (sink=0x23873d30,
event=0x21428960) at gstappsink.c:686
#3  0x00007f9c2e00fd14 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstbase-1.0.so.0
#4  0x00007f9c2e8dd837 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#5  0x00007f9c2e8ddcfe in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#6  0x00007f9c2e8de110 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#7  0x00007f9c2e8dbcff in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#8  0x00007f9c2e8e8061 in gst_pad_push_event () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#9  0x00007f9c2e8e81de in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#10 0x00007f9c2e8e3a7e in gst_pad_forward () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#11 0x00007f9c2e8e3bd3 in gst_pad_event_default () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#12 0x00007f9c2e8dd837 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#13 0x00007f9c2e8ddcfe in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#14 0x00007f9c2e8de110 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#15 0x00007f9c2e8dbcff in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#16 0x00007f9c2e8e8061 in gst_pad_push_event () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#17 0x00007f9c2e02b56d in ?? () from
/usr/lib/x86_64-linux-gnu/libgstbase-1.0.so.0
#18 0x00007f9c2e8dd837 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#19 0x00007f9c2e8ddcfe in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#20 0x00007f9c2e8de110 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#21 0x00007f9c2e8dbcff in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#22 0x00007f9c2e8e8061 in gst_pad_push_event () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#23 0x00007f9c2e02b56d in ?? () from
/usr/lib/x86_64-linux-gnu/libgstbase-1.0.so.0
#24 0x00007f9c2e8dd837 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#25 0x00007f9c2e8ddcfe in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#26 0x00007f9c2e8de110 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#27 0x00007f9c2e8dbcff in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#28 0x00007f9c2e8e8061 in gst_pad_push_event () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#29 0x00007f9c2e02b56d in ?? () from
/usr/lib/x86_64-linux-gnu/libgstbase-1.0.so.0
#30 0x00007f9c2e8dd837 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#31 0x00007f9c2e8ddcfe in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#32 0x00007f9c2e8de110 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#33 0x00007f9c2e8dbcff in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#34 0x00007f9c2e8e8061 in gst_pad_push_event () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#35 0x00007f9c2e8e81de in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#36 0x00007f9c2e8e3a7e in gst_pad_forward () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#37 0x00007f9c2e8e3bd3 in gst_pad_event_default () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#38 0x00007f9c2d985376 in gst_play_sink_convert_bin_sink_event
(pad=0x212ed170, parent=0x2146ac60, event=0x21428960) at
gstplaysinkconvertbin.c:260
#39 0x00007f9c2e8dd837 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#40 0x00007f9c2e8ddcfe in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#41 0x00007f9c2e8de110 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#42 0x00007f9c2e8dbcff in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#43 0x00007f9c2e8e8061 in gst_pad_push_event () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#44 0x00007f9c2c910d58 in ?? () from
/usr/lib/x86_64-linux-gnu/gstreamer-1.0/libgstcoreelements.so
#45 0x00007f9c2e912a21 in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#46 0x00007f9c87affdce in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#47 0x00007f9c87aff3d5 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#48 0x00007f9d08468494 in start_thread (arg=0x7f9c2b2a3700) at
pthread_create.c:333
#49 0x00007f9d08766aff in clone () at
../sysdeps/unix/sysv/linux/x86_64/clone.S:97


Thread 3 (Thread 0x7f77c6454700 (LWP 66663)):
#0  syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
#1  0x00007f779bd3587c in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#2  0x00007f779b1d578c in ?? () from
/usr/lib/x86_64-linux-gnu/libgstbase-1.0.so.0
#3  0x00007f779c26872e in gst_element_change_state () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#4  0x00007f779c268e9f in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#5  0x00007f779c2471ad in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#6  0x00007f779c26872e in gst_element_change_state () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#7  0x00007f779c268e9f in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#8  0x00007f779c2471ad in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#9  0x00007f779990a138 in gst_play_sink_change_state (element=0xe620500,
transition=GST_STATE_CHANGE_PLAYING_TO_PAUSED) at gstplaysink.c:4872
#10 0x00007f779c26872e in gst_element_change_state () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#11 0x00007f779c268e9f in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#12 0x00007f779c2471ad in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#13 0x00007f779c28c73a in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#14 0x00007f77998fb84f in gst_play_bin_change_state (element=0xe61bb10,
transition=GST_STATE_CHANGE_PLAYING_TO_PAUSED) at gstplaybin2.c:5768
#15 0x00007f779c26872e in gst_element_change_state () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#16 0x00007f779c268e9f in ?? () from
/usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0
#17 0x00007f779c54a6c8 in (anonymous namespace)::changeElementState
(element=0xe61bb10, newState=newState at entry=@0x7f77c64488b0:
GST_STATE_NULL, timeToWait=5000000000)
<my application specific trace>


This used to work fine on Debian 8. However, on Debian 9 and Ubuntu 16.04
and higher which have Gstreamer versions 1.8 and higher, this happens.

My application is multi-threaded and below is a brief description:
Main Thread:
-> Creates playbin and appsink
-> Connects them
-> Runs the pipeline
-> Stop the pipeline either upon EOF or upon request

Thread 2:
--> Pulls samples from the appsink

I have confirmed that Thread 2 is completely shutdown when the Main thread
is attempting to stop the pipeline i.e. there is no situation when I am
attempting to change state in the middle of a call to
gst_app_sink_pull_sample.

I attempted to use a pad probe which was recommended when wanting to play
only a portion of a media file as per
https://gstreamer.freedesktop.org/documentation/application-development/advanced/pipeline-manipulation.html

However, I do not believe that this will work for me because I do not know
which portion of the media file is to be played in advance i.e. users can
stop playback at anytime.

After I added the probe, I noticed that the frequency of the stalls reduced
quite drastically i.e. from everytime to 1 in 500. My pad probe callback is
as below:

// If the stopping of the playbin has not been initiated,
    // then allow the sample to pass through.
    if( !_isPlaybinToBeStopped )
    {
        return GST_PAD_PROBE_PASS;
    }

    BOOST_SCOPE_EXIT((&_isPlaybinToBeStopped))
    {
        _isPlaybinToBeStopped = false;
    }
    BOOST_SCOPE_EXIT_END

    // Remove the pad probe if the playbin is to be stopped.
    return GST_PAD_PROBE_REMOVE;

I really do not understand how adding this probe is really helping because
it does no action other than pass through OR just remove the probe. Am I
just getting lucky?

Any thoughts? As this happens only for Mp3 files, is this a bug?

Dinesh
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