[Discussion] Did you ever forget to un_ref any GObject?

[Sérgio Agostinho]

This is a very informative response that should be incorporated into to
Gstreamer's application development manual.

2015-01-09 10:02 GMT+01:00 Sebastian Dröge <sebastian at centricular.com>:

> On Di, 2015-01-06 at 18:10 -0800, hxpax wrote:
> > That could be a big problem on some other platforms, more than just a
> > segfault.
>
> It could result in worse situations, yes.
>
> > I wonder are there any conventions for unref?
>
> The docs would tell you, they now have annotations on parameters and
> return values hopefully everywhere. Like (transfer none), (transfer
> full), (transfer container) and (transfer floating).
>
> none: for return values you don't own it and must not unref it, for
> parameters you still own it and must unref it
>
> full: for return values you own it and must unref it, for parameters you
> don't own it anymore and must get another reference with ref before
> passing it to the function if you still need it afterwards
>
> container: only used for containers, e.g. lists. Means the same as
> transfer full for the actual container, but transfer none for the
> elements of the container
>
> floating: tricky one, check the documentation for floating references
> first. It means for return values that you get a floating reference, for
> parameters it means that it is transfer full for floating references and
> transfer none for non-floating references.
>
>
> General rule is that setter should be transfer none, getter transfer
> full, adder (e.g. gst_bin_add()) transfer full or transfer floating.
> Exception for getters (and things like gst_message_parse_*) are things
> like GstStructure, GstMessage, etc where the return value is transfer
> none and stays valid as long as you have a reference to its container.
> Functions that take a const pointer or return one are by definition
> transfer none.
>
> Things that pass buffers/messages/events on to other pads/elements are
> transfer full (e.g. gst_pad_push(), gst_element_post_message()), query
> related things are transfer none. Reason is that you usually want to get
> rid of the references of the former when passing it (also to keep
> buffers writable downstream if possible), while for queries you still
> want to own the reference (how would you otherwise get the query result
> later?).
>
> Unfortunately there are a few inconsistencies and exceptions to these
> rules.
>
> Hope this helps!
>
> --
> Sebastian Dröge, Centricular Ltd · http://www.centricular.com
>
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>
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