[FFmpeg-devel] [PATCH] ffmpeg: make reading packets from thread blocking.

[Michael Niedermayer]

On Fri, Oct 25, 2013 at 11:33:00AM +0200, Nicolas George wrote:
> If a packet is not ready on the input selected by ffmpeg,
> it will read from another input instead. If that happens
> repeatedly, frames will accumulate somewhere later in the
> processing to ensure streams synchronization. It can happen
> in particular when reading from a slow medium or an
> expensive lavfi filter graph.
> 
> Make reading from normal demuxers on non-streamed data and
> from the lavfi pseudo-device blocking to avoid that.
> 
> Should fix trac ticket #3079.
> 
> Signed-off-by: Nicolas George <george at nsup.org>
> ---
>  ffmpeg.c | 17 +++++++++++++++--
>  ffmpeg.h |  1 +
>  2 files changed, 16 insertions(+), 2 deletions(-)
> 
> 
> Note: the non_blocking flag can be later made an option. But I am in fact
> rather convinced that the blocking mode should be made the default even for
> devices, possibly enlarging the size of the FIFO at the same time.
> 
> 
> diff --git a/ffmpeg.c b/ffmpeg.c
> index 001e5c1..ff717d5 100644
> --- a/ffmpeg.c
> +++ b/ffmpeg.c
> @@ -2795,6 +2795,7 @@ static void *input_thread(void *arg)
>  
>          av_dup_packet(&pkt);
>          av_fifo_generic_write(f->fifo, &pkt, sizeof(pkt), NULL);
> +        pthread_cond_signal(&f->fifo_cond);
>  
>          pthread_mutex_unlock(&f->fifo_lock);
>      }
> @@ -2851,6 +2852,10 @@ static int init_input_threads(void)
>          if (!(f->fifo = av_fifo_alloc(8*sizeof(AVPacket))))
>              return AVERROR(ENOMEM);
>  
> +        if (f->ctx->pb ? !f->ctx->pb->seekable :
> +            strcmp(f->ctx->iformat->name, "lavfi"))
> +            f->non_blocking = 1;
> +
>          pthread_mutex_init(&f->fifo_lock, NULL);
>          pthread_cond_init (&f->fifo_cond, NULL);
>  
> @@ -2866,14 +2871,22 @@ static int get_input_packet_mt(InputFile *f, AVPacket *pkt)
>  
>      pthread_mutex_lock(&f->fifo_lock);
>  
> +    while (1) {
>      if (av_fifo_size(f->fifo)) {
>          av_fifo_generic_read(f->fifo, pkt, sizeof(*pkt), NULL);
>          pthread_cond_signal(&f->fifo_cond);
> +        break;
>      } else {
> -        if (f->finished)
> +        if (f->finished) {
>              ret = AVERROR_EOF;
> -        else
> +            break;
> +        }
> +        if (f->non_blocking) {
>              ret = AVERROR(EAGAIN);
> +            break;
> +        }
> +        pthread_cond_wait(&f->fifo_cond, &f->fifo_lock);
> +    }
>      }

this code deadlocked 1 out of 2 make -j12 fate

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In a rich man's house there is no place to spit but his face.
-- Diogenes of Sinope
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