[Bug 693800] New: Problem with ref counter in adding/removing element to/from bin more than once

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=693800
  GStreamer | gstreamer (core) | 1.x

           Summary: Problem with ref counter in adding/removing element
                    to/from bin more than once
    Classification: Platform
           Product: GStreamer
           Version: 1.x
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gstreamer (core)
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: alexas at axis.com
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


This case:

  GstElement *element = gst_element_factory_make("fakesink", NULL);
  GstBin *bin = (GstBin*)gst_bin_new("test");
  g_print("refcount: %u\n", GST_OBJECT_REFCOUNT(element));
  gst_bin_add(bin, gst_object_ref(element));
  g_print("refcount: %u\n", GST_OBJECT_REFCOUNT(element));
  gst_bin_remove(bin, element);
  g_print("refcount: %u\n", GST_OBJECT_REFCOUNT(element));
  gst_bin_add(bin, gst_object_ref(element));
  g_print("refcount: %u\n", GST_OBJECT_REFCOUNT(element));
  gst_bin_remove(bin, element);

Should result in the refcount being 'stable' since gst_bin_add has a full
transfer and to keep the ref outside you need to ref once more. This is not the
case however, the ref increases. The scary part is that it does not increase
the first time. The reason is that part of the operation is
gst_object_set_parent, which takes the floating reference. The first time we do
this the element is indeed floating and the ref count is not changed, the rest
of the time it will increase the ref by one.

If we do indeed want the floating ref to behave as it does then we need to
unref when setting parent to NULL in bin_remove (we just set the variable to
NULL right now). This will however cause the ref count to drop to zero since we
'steal' a reference count from the outside when doing that (the floating one).
I will take a look at a possible solution tomorrow.

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