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

[Xiang, Haihao]

On Thu, 2021-12-23 at 14:01 +0000, Xiang, Haihao wrote:
> 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 ? 

Any other comment for this patch version? I'll add the note pointed out by Lynne
and push this patch if no objection. 

Thanks
Haihao