[FFmpeg-devel] [PATCH] pthread_frame: set err from the thread that return frame

[Muhammad Faiz]

On Wed, Apr 26, 2017 at 10:34 PM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
> Hi,
>
> On Wed, Apr 26, 2017 at 1:21 AM, Muhammad Faiz <mfcc64 at gmail.com> wrote:
>
>> On Wed, Apr 26, 2017 at 4:09 AM, wm4 <nfxjfg at googlemail.com> wrote:
>> > On Tue, 25 Apr 2017 23:52:04 +0700
>> > Muhammad Faiz <mfcc64 at gmail.com> wrote:
>> >
>> >> when frame is received, not from other threads.
>> >>
>> >> Should fix fate failure with THREADS>=4:
>> >>   make fate-h264-attachment-631 THREADS=4
>> >>
>> >> Signed-off-by: Muhammad Faiz <mfcc64 at gmail.com>
>> >> ---
>> >>  libavcodec/pthread_frame.c | 4 ++++
>> >>  1 file changed, 4 insertions(+)
>> >>
>> >> diff --git a/libavcodec/pthread_frame.c b/libavcodec/pthread_frame.c
>> >> index 13d6828..c452ed7 100644
>> >> --- a/libavcodec/pthread_frame.c
>> >> +++ b/libavcodec/pthread_frame.c
>> >> @@ -547,6 +547,10 @@ int ff_thread_decode_frame(AVCodecContext *avctx,
>> >>
>> >>      fctx->next_finished = finished;
>> >>
>> >> +    /* if frame is returned, properly set err from the thread that
>> return frame */
>> >> +    if (*got_picture_ptr)
>> >> +        err = p->result;
>> >> +
>> >>      /* return the size of the consumed packet if no error occurred */
>> >>      if (err >= 0)
>> >>          err = avpkt->size;
>> >
>> > Well, the logic confuses me. Does this override an earlier set err
>> > value?
>>
>> Yes, because an earlier set err value may be from a different thread.
>>
>> >Could err be set to the correct value in the first place (inside
>> > of the loop)?
>>
>> No, it was intended on 32a5b631267
>
>
> Thanks for working on this. It's good to get more people familiar with this
> code.
>
> So, I'm looking at understanding this, you're trying to fix the case where
> during draining, we may iterate over >1 worker thread cases where the first
> returned an error code without having decoded a frame, and the second
> decoded a frame without returning an error code, right? The current code
> would return a frame with an error return code, which I believe is then
> ignored by the user thread.
>
> So, you're basically trying to say that instead, we should ignore the
> error. I agree that fixes the issue of md5 mismatch w/ vs. w/o threads, but
> I doubt that it's fundamentally more correct, because the user thread still
> misses out on error codes from the worker threads. Wouldn't you agree that
> we should - even during draining - not iterate over N threads, but just the
> next thread, and return either an error or a decoded frame, and keep doing
> that until all worker threads are flushed, which we can then signal e.g. by
> return=0 and *got_picture_ptr=0?

The problem is that return<0 and *got_picture_ptr==0 is also
considered as eof when avpkt->size==0.