[Bug 782499] New: Floating references confusion

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=782499

            Bug ID: 782499
           Summary: Floating references confusion
    Classification: Platform
           Product: GStreamer
           Version: unspecified
                OS: Linux
            Status: NEW
          Severity: major
          Priority: Normal
         Component: gstreamer (core)
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: slomo at coaxion.net
        QA Contact: gstreamer-bugs at lists.freedesktop.org
        Depends on: 702960, 730138, 743062, 747990
     GNOME version: ---

This is a tracker bug, with some background and general solution. See below

Related bugs (at least):
https://bugzilla.gnome.org/show_bug.cgi?id=702960
https://bugzilla.gnome.org/show_bug.cgi?id=730138
https://bugzilla.gnome.org/show_bug.cgi?id=743062
https://bugzilla.gnome.org/show_bug.cgi?id=747990

And background info for GI here:
https://bugzilla.gnome.org/show_bug.cgi?id=657202
https://bugzilla.gnome.org/show_bug.cgi?id=742618

And about floating references in general here:
https://developer.gnome.org/gobject/stable/gobject-The-Base-Object-Type.html#floating-ref

=========================

There are currently 3 distinct problems here

1) Bug #730138 and bug #702960 (and
https://bugzilla.gnome.org/show_bug.cgi?id=702960#c25 especially). Functions
taking a parameter and calling g_object_ref_sink() on them. According to GI and
bindings developers, these should be "transfer none" (aka "transfer floating"),
and this is what GTK+ does at least. We currently do "transfer full", which
causes leaks in bindings.

I would propose to mark these all "transfer floating" (aka "transfer none").
This keeps intention in the API docs ("floating") and makes bindings work.

Currently bindings have overrides for our API (or in the case of Python just
leak), and this shouldn't be necessary. We should do as a)
GObject-Introspection developers and bindings developers say (see links above),
and b) as bindings that work well (GTK especially) do. If we diverge from that,
problems will appear.

2) Bug #747990. Our functions that ref_sink() (directly or indirectly) are
inconsistent with that, and often behave different in error paths. This should
obviously be fixed. That bug has an initial patch but it is not complete, see
also https://bugzilla.gnome.org/show_bug.cgi?id=702960#c25

3) Bug #743062. We have a couple of GstObjects that are ref_sink()'d in their
instance_init / GObject::constructor. This causes leaks in bindings as they
have no way of knowing about that when using g_object_new(), as most bindings
do. For the explicit constructors (gst_bin_new()) there are annotations
("transfer floating" aka "transfer none" in the case of not ref_sinking, or
"transfer full" otherwise (control sources, clocks, etc.). Note that the second
case seems to be generally wrong currently!

I would propose to ref_sink() these objects in the explicit constructor (the
new() functions) instead of instance_init / GObject::constructor, and fix up
the annotations of them.


Any other thoughts on this? I would suggest to fix this for 1.14, ASAP to give
it a lot of testing time.

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