Re: [Discuss] Make a thinner Glib/GTK+ to fit tiny device better

[cee1 <fykcee1 gmail com>]

2015-10-17 3:29 GMT+08:00 Nicolas Dufresne <nicolas dufresne collabora com>:
> Le samedi 17 octobre 2015 à 01:20 +0800, cee1 a écrit :
> > 2015-10-16 23:46 GMT+08:00 Florian Müllner <fmuellner gnome org>:
> > > On Fri, Oct 16, 2015 at 5:38 PM, cee1 <fykcee1 gmail com> wrote:
> > > > If yes, we may let GObject inherit from
> > > > GstMiniObject to obtain the COW feature?
> > >
> > > This would break ABI, so not something you should expect any time
> > soon.
> >
> > So what about GObject2(a bit likes playbin2 in GStreamer)? Code can
> > change to inherit from it and recompiling...
>
> That's an extremely ugly fallback solution, specially for a feature
> that no one will use.
>
> The problem here is that GObject cannot be copied generically, when
> they are, it's a custom feature. Note that reference based locking
> isn't always great. If I was to redo that, I'm opt for explicit locking
> instead. In GStreamer we have hit many of the limitation of this model.
> This can of course be introduced with an GInterface if you drop this cr
> azy idea of using ref-count to figure-out writability.
Is there any examples about the limitation of this reference count
based model at hand?

So can I say gstreamer use COW mainly for locking(similar to RCU), not
for the purpose of removing duplication?

For comparison, IIUIC, EFL implements a GSlice (some what)equivalent
layer[1], but provides COW-able memory objects. It will even find
memory objects which have the same content and merge them in idle,
according to the article
https://phab.enlightenment.org/phame/live/1/post/efl_memory_consumption_moo/.

BTW, I go through internal of gst_mini_object_make_writable, and
following logical seems confused:
"""
http://cgit.freedesktop.org/gstreamer/gstreamer/tree/gst/gstminiobject.c#n190

gst_mini_object_lock()
...
    if (access_mode & GST_LOCK_FLAG_EXCLUSIVE) {
      /* shared ref */
      newstate += SHARE_ONE;
      access_mode &= ~GST_LOCK_FLAG_EXCLUSIVE;
    }
"""

Why under an EXCLUSIVE mode, a mini object can be shared?



---
1. https://docs.enlightenment.org/stable/efl/group__Eina__Cow__Group.html


Regards,

- cee1