[FFmpeg-devel] [PATCH 1/4] lavu: add simple array implementation

[wm4]

On Mon, 3 Mar 2014 11:33:20 +0100
Michael Niedermayer <michaelni at gmx.at> wrote:

> On Mon, Mar 03, 2014 at 11:00:18AM +0100, Lukasz M wrote:
> > W dniu poniedziałek, 3 marca 2014 Michael Niedermayer <michaelni at gmx.at>
> > napisał(a):
> > 
> > > On Mon, Mar 03, 2014 at 01:59:43AM +0100, Lukasz Marek wrote:
> > > >
> > > > >You're adding it to lavu, and it's not marked as internal/experimental.
> > > If
> > > > >it stinks or needs 3 API updates or re-implementations, the old cruft
> > > > >sticks around for years to come.
> > > >
> > > > Can you precise how to mark it? I added it as public, but don't
> > > > understand how can i make it experimental.
> > > >
> > >
> > > > >That's why we now have 2 (and with yours, soon 3) array implementations.
> > > > >Can we stick to one? At least java uses the same API for all its
> > > array/list
> > > > >things.
> > > >
> > > > The existing two doesn't allow to free "objects" with allocated
> > > > pointers inside. If you fix them then you have 4. I really think it
> > > > is better to have one common for wide range of use cases. I can
> > > > refactor existing code to use mine if accepted.
> > >
> > > if i have an array of "object" with pointers inside them and want
> > > to free them id do
> > >
> > > for(i=0; i<arraysize; i++)
> > >     my_free(my_array + i);
> > >
> > > that needs no API beyond ANSI/ISO C
> > > what am i missing ?
> > >
> > 
> > nothing. existing array impl is not so smart to do that on memory
> > allocation fail AFAIR.
> 
> maybe it could be solved with something like
> int av_dynarray_add_nofree(...)
> 
> which would not free the array on failure but return an error code
> and leave deallocation (if needed) to the caller

Freeing the whole array just because adding one element failed sounds
quite idiotic. (Though I guess it's ok for certain use cases, like
initialization.) But apparently these are the existing semantics. Adding
the function you propose sounds like a good idea.

Even with the av_dynarray_add() semantics, one could just pass a free
callback to the function, instead of needing an array struct.

By the way, av_dynarray_add() seems to violate strict aliasing rules...