[FFmpeg-devel] [PATCH v4 1/1] avutils/hwcontext: When deriving a hwdevice, search for existing device in both directions

[Xiang, Haihao]

On Fri, 2021-11-26 at 19:29 +0000, Soft Works wrote:
> > -----Original Message-----
> > From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of Anton
> > Khirnov
> > Sent: Friday, November 26, 2021 8:12 PM
> > To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org>
> > Subject: Re: [FFmpeg-devel] [PATCH v4 1/1] avutils/hwcontext: When deriving
> > a
> > hwdevice, search for existing device in both directions
> > 
> > Quoting Soft Works (2021-11-26 19:43:58)
> > > Maybe I'm missing something, but hw device contexts are refcounted.
> > > What happens in hwdevice_ctx_free() is this:
> > > 
> > > av_buffer_unref(&ctx->internal->source_device);
> > 
> > IIUC this only happens after the parent device is freed. My concern is
> > the following situation:
> > - the caller creates a parent hwdevice
> > - the caller derives a child from it, which may acquire some additional
> >   resources beyond what the parent holds
> > - the caller unrefs all his references to the child, but the child does
> >   not get freed because the parent still holds a reference to it
> > 
> > Since av_hwdevice_ctx_create_derived() has a flags parameter, we might
> > want to introduce a flag to control this behavior.
> 
> I understand what you mean. I'm just not sure whether a practical case
> with such a requirement exists. Should that turn out to be required,
> such flag can be added at any time, IMO.


I agree we may add such flag later if required. May we merge this patch to fix
the annoying derivation limitation if no other concern ? 

Thanks
Haihao