[FFmpeg-devel] [PATCH] ffplay's primary function is not to trigger OOM killer

[Michael Niedermayer]

On Thu, Feb 19, 2009 at 11:42:18PM +0100, Aurelien Jacobs wrote:
> Michael Niedermayer wrote:
> 
> > On Thu, Feb 19, 2009 at 10:00:10PM +0100, Aurelien Jacobs wrote:
> > > Hi,
> > > 
> > > Commit r16484 introduced an infinite loop allocating memory in ffplay.
> > > This is very efficient at filling memory and triggering the OOM killer.
> > > The relevant part of the main loop now looks like this:
> > > 
> > >     for(;;) {
> > >         [...]
> > >         if(url_feof(ic->pb)) {
> > >             av_init_packet(pkt);
> > >             [...]
> > >             packet_queue_put(&is->videoq, pkt);
> > >             continue;
> > >         }
> > >         ret = av_read_frame(ic, pkt);
> > >         if (ret < 0) {
> > >             [...]
> > >             break;
> > >         }
> > >         [...]
> > >         packet_queue_put(&is->videoq, pkt);
> > >     }
> > > 
> > > So when the demuxer read the last frame of the stream, the ByteIOContext
> > > reaches EOF but av_read_frame() correctly return a positive value as it
> > > actually read a full frame.
> > > Then at next iteration of the main loop url_feof() is triggered, which
> > > allocate a new packet and go back to the start of the loop, and
> > > triggers url_feof() again, and so on.
> > 
> > try to RTFS again and harder, these kind of bug analysis and fixes is what
> > leds projects to become what mplayer did ...
> 
> try to RTFS a bit more before writing such reply ;-)

indeed i should


> 
> > see, straight before the eof case:
> > 
> >         /* if the queue are full, no need to read more */
> >         if (is->audioq.size > MAX_AUDIOQ_SIZE ||
> >             is->videoq.size > MAX_VIDEOQ_SIZE ||
> >             is->subtitleq.size > MAX_SUBTITLEQ_SIZE) {
> >             /* wait 10 ms */
> >             SDL_Delay(10);
> >             continue;
> >         }
> > 
> > thus the NULL packets are only inserted if the que is not full,
> 
> Right. But the definition of "queue is not full" may not be what you
> would expect.
> 
> > this effectively limits the size and cannot trigger OOM (in theory ...)
> 
> No. This only limits the sum of all pkt.size. But this don't prevent
> adding infinite amount of 0 sized packets. The total size of actual
> data is indeed 0, but the size of the structures containing those
> empty data is enough to fill memory...

what about adding sizeof(the struct) to the size used in _put and _get?
should also be conceptually be more correct as it better represents the
memory actually used by the que

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Concerning the gods, I have no means of knowing whether they exist or not
or of what sort they may be, because of the obscurity of the subject, and
the brevity of human life -- Protagoras
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