[FFmpeg-devel] [PATCH] avcodec/mpegvideo: Fix all but one tsan warning in fate-vsynth1-mpeg4

[wm4]

On Sun, 9 Jul 2017 22:37:46 -0400
"Ronald S. Bultje" <rsbultje at gmail.com> wrote:

> Hi,
> 
> On Sun, Jul 9, 2017 at 9:19 PM, Michael Niedermayer <michael at niedermayer.cc>
> wrote:
> 
> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > ---
> >  libavcodec/mpegvideo.c | 15 ++++++++++++++-
> >  1 file changed, 14 insertions(+), 1 deletion(-)
> >
> > diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
> > index e29558b3a2..574b3854e0 100644
> > --- a/libavcodec/mpegvideo.c
> > +++ b/libavcodec/mpegvideo.c
> > @@ -495,7 +495,20 @@ int ff_mpeg_update_thread_context(AVCodecContext
> > *dst,
> >      // in that case dst may need a reinit
> >      if (!s->context_initialized) {
> >          int err;
> > -        memcpy(s, s1, sizeof(MpegEncContext));
> > +#define COPY(x) s->x = s1->x;
> >  
> 
> Unused?
> 
> 
> > +#define COPYR(a, b) memcpy(&s->a, &s1->a, ((uint8_t*)&s->b) -
> > ((uint8_t*)&s->a))
> > +        COPYR(h263_aic,                         qscale);
> > +        COPYR(lambda,                           mv_dir);
> > +        COPYR(no_rounding,                      dest);
> > +        COPYR(mb_index2xy,                      resync_mb_x);
> > +        COPYR(next_p_frame_damaged,             h263_aic_dir);
> > +        COPYR(h263_slice_structured,            mcsel);
> > +        COPYR(quant_precision,                  first_slice_line);
> > +        COPYR(flipflop_rounding,                gb);
> > +        COPYR(gop_picture_number,               picture_structure);
> > +        COPYR(picture_structure,                pblocks);
> > +        COPYR(decode_mb,                        er);
> > +        COPYR(error_rate,                       noise_reduction);  
> 
> 
> This is very obscure... The obscure part is what happens when fields get
> (through refactoring) reordered or new fields get inserted...
> 
> I also appear to remember that we used to use this same pattern for h264
> also, but we don't anymore. Does anyone remember why?

Do you mean 0ba471d7d864c712f45d7ac6aca4829aba025adc?

    h264: eliminate copy_fields
    
    It is very fragile against fields being moved and hides what is actually
    being copied. Copy all the fields explicitly instead.

Seems justification enough for me.