Element never gets disposed when using python bindings

[viktor.chvatal]

Hi,

I have been tracking a memory leak in our gstreamer application for last two
days, and I have been able to simplify the case into this situation: I
create a pipeline and an element, put the element into the pipeline, than
set the pipeline state to NULL. The pipeline gets disposed, but the element
in it does not. This is the Python code to reproduce the behavior:
----------
import gi
gi.require_version('Gst', '1.0')
from gi.repository import Gst

def run():
    pipeline = Gst.Pipeline(name = 'pipeline')
    pipeline.add(Gst.ElementFactory.make('videotestsrc', 'my_elem'))
    pipeline.set_state(Gst.State.NULL)
    del pipeline
    pipeline = None
    input()

def main():
    Gst.init(None)
    run()

if __name__ == '__main__':
    main()
----------

When I run the code with GST_DEBUG=8, let it wait inside the input()
function and grep dispose, I see that the pipeline disposed correctly:

gst_pipeline_dispose:<pipeline> dispose
gst_bin_dispose:<pipeline> dispose
gst_object_dispose:<bus0> dispose
gst_element_dispose:<pipeline> dispose
gst_object_dispose:<bus1> dispose
gst_element_dispose:<pipeline> parent class dispose
gst_object_dispose:<pipeline> dispose

When I look at my_elem using grep REFCOUNTING | grep my_elem:

gst_object_set_parent:<my_elem> set parent (ref and sink)
gst_object_ref_sink:<my_elem> 0x25992d0 ref_sink 2->3
gst_object_unref:<my_elem> 0x25992d0 unref 2->1

I see that my_elem ends with ref count 1 and stays allocated. I tried to
reproduce this case in C code as closely as possible:
----------
#include <stdio.h>
#include <gst/gst.h>

int run() {
    GstElement *detector = gst_element_factory_make ("videotestsrc",
"my_elem");
    GstElement *pipeline = gst_pipeline_new ("pipeline");
    gst_bin_add (GST_BIN (pipeline), detector);

    gst_element_set_state (pipeline, GST_STATE_NULL);
    gst_object_unref (pipeline);

    getchar();
}

int main()
{
    gst_init (NULL, NULL);
    run ();
    gst_deinit ();
    return 0;
}
----------

Now, my_elem gets disposed as expected after its refcount reaches 0:

gst_object_set_parent:<my_elem> set parent (ref and sink)
gst_object_ref_sink:<my_elem> 0x11530e0 ref_sink 1->2
gst_object_unref:<my_elem> 0x11530e0 unref 1->0
gst_element_dispose:<my_elem> dispose
gst_object_unparent:<my_elem:src> unparent
gst_element_dispose:<my_elem> parent class dispose
gst_object_dispose:<my_elem> dispose
gst_element_finalize:<my_elem> finalize
gst_element_finalize:<my_elem> finalize parent
gst_object_finalize:<my_elem> finalize

Any ideas why Python bindings behave differently or what to try in order to
dispose the element?

Tested on Debian Jessie and GStreamer 1.4.4



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[Sebastian Dröge-3]

On Fri, 2018-03-23 at 02:51 -0700, viktor.chvatal wrote:
> [...]
>
> Tested on Debian Jessie and GStreamer 1.4.4

This is a known problem and was fixed with 1.14:
  https://bugzilla.gnome.org/show_bug.cgi?id=730138

(and a couple of similar cases elsewhere)

--
Sebastian Dröge, Centricular Ltd · https://www.centricular.com

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