[FFmpeg-devel] [PATCH] ffmpeg: fix deadlock regression in threading error handing

Nicolas George george at nsup.org
Fri Jun 27 17:20:10 CEST 2014


Le nonidi 9 messidor, an CCXXII, Sergey a écrit :
> Commit fc9c857c introduced deadlock regression when processing too many inputs:
>   ffmpeg $(seq -f " -f lavfi -i aevalsrc=0:d=%.0f" 70) -vf concat=n=70:v=0:a=1 -f null -
> Happens for different number of inputs, depending on available memory size,
> overcommit settings, ulimits, etc. Easily noticeable for 32-bit builds,
> that exhaust address space allocating 8-10 MB stack for each thread.
> Earlier ffmpeg versions exited with unhelpful "Conversion failed!" message.
> 
> This patch fixes both problems: it frees the queue to prevent deadlock
> and adds a meaningful error message if pthread_create() fails.
> 
> ---
> diff --git a/ffmpeg.c b/ffmpeg.c
> index 2c17525..ce4b8f5 100644
> --- a/ffmpeg.c
> +++ b/ffmpeg.c
> @@ -3237,8 +3237,11 @@ static int init_input_threads(void)
>          if (ret < 0)
>              return ret;
>  
> -        if ((ret = pthread_create(&f->thread, NULL, input_thread, f)))
> +        if ((ret = pthread_create(&f->thread, NULL, input_thread, f))) {
> +            av_log(NULL, AV_LOG_ERROR, "pthread_create failed: %s. Try to increase `ulimit -v` or decrease `ulimit -s`.\n", strerror(ret));
> +            av_thread_message_queue_free(&f->in_thread_queue);
>              return AVERROR(ret);
> +        }
>      }
>      return 0;
>  }

I am not maintainer of ffmpeg.c but responsible for commit fc9c857c, and as
such I say this looks correct. free_input_threads() try to drain the queues,
and it will not be able to if there is no sending thread.

Thanks.

Regards,

-- 
  Nicolas George
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