[FFmpeg-devel] [PATCH v2] avcodec/pthread_frame, decode: allow errors to happen on draining

[Muhammad Faiz]

So, all frames and errors are correctly reported in order.
Also limit the numbers of error during draining to prevent infinite loop.

This fix fate failure with THREADS>=4:
  make fate-h264-attachment-631 THREADS=4
This also reverts a755b725ec1d657609c8bd726ce37e7cf193d03f.

Suggested-by: wm4, Ronald S. Bultje, Marton Balint
Signed-off-by: Muhammad Faiz <mfcc64 at gmail.com>
---
 libavcodec/decode.c        | 21 +++++++++++++++++++--
 libavcodec/internal.h      |  3 +++
 libavcodec/pthread_frame.c | 15 +++++++--------
 3 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/libavcodec/decode.c b/libavcodec/decode.c
index 6ff3c40..edfae55 100644
--- a/libavcodec/decode.c
+++ b/libavcodec/decode.c
@@ -568,8 +568,24 @@ FF_ENABLE_DEPRECATION_WARNINGS
         avctx->time_base = av_inv_q(av_mul_q(avctx->framerate, (AVRational){avctx->ticks_per_frame, 1}));
 #endif
 
-    if (avctx->internal->draining && !got_frame)
-        avci->draining_done = 1;
+    /* do not stop draining when got_frame != 0 or ret < 0 */
+    if (avctx->internal->draining && !got_frame) {
+        if (ret < 0) {
+            /* prevent infinite loop if a decoder wrongly always return error on draining */
+            /* reasonable nb_errors_max = maximum b frames + thread count */
+            int nb_errors_max = 20 + (HAVE_THREADS && avctx->active_thread_type & FF_THREAD_FRAME ?
+                                avctx->thread_count : 1);
+
+            if (avci->nb_draining_errors++ >= nb_errors_max) {
+                av_log(avctx, AV_LOG_ERROR, "Too many errors when draining, this is a bug. "
+                       "Stop draining and force EOF.\n");
+                avci->draining_done = 1;
+                ret = AVERROR_BUG;
+            }
+        } else {
+            avci->draining_done = 1;
+        }
+    }
 
     avci->compat_decode_consumed += ret;
 
@@ -1659,6 +1675,7 @@ void avcodec_flush_buffers(AVCodecContext *avctx)
 {
     avctx->internal->draining      = 0;
     avctx->internal->draining_done = 0;
+    avctx->internal->nb_draining_errors = 0;
     av_frame_unref(avctx->internal->buffer_frame);
     av_frame_unref(avctx->internal->compat_decode_frame);
     av_packet_unref(avctx->internal->buffer_pkt);
diff --git a/libavcodec/internal.h b/libavcodec/internal.h
index 84d3362..caa46dc 100644
--- a/libavcodec/internal.h
+++ b/libavcodec/internal.h
@@ -200,6 +200,9 @@ typedef struct AVCodecInternal {
     int showed_multi_packet_warning;
 
     int skip_samples_multiplier;
+
+    /* to prevent infinite loop on errors when draining */
+    int nb_draining_errors;
 } AVCodecInternal;
 
 struct AVCodecDefault {
diff --git a/libavcodec/pthread_frame.c b/libavcodec/pthread_frame.c
index 13d6828..363b139 100644
--- a/libavcodec/pthread_frame.c
+++ b/libavcodec/pthread_frame.c
@@ -509,8 +509,8 @@ int ff_thread_decode_frame(AVCodecContext *avctx,
     /*
      * Return the next available frame from the oldest thread.
      * If we're at the end of the stream, then we have to skip threads that
-     * didn't output a frame, because we don't want to accidentally signal
-     * EOF (avpkt->size == 0 && *got_picture_ptr == 0).
+     * didn't output a frame/error, because we don't want to accidentally signal
+     * EOF (avpkt->size == 0 && *got_picture_ptr == 0 && err >= 0).
      */
 
     do {
@@ -526,20 +526,19 @@ int ff_thread_decode_frame(AVCodecContext *avctx,
         av_frame_move_ref(picture, p->frame);
         *got_picture_ptr = p->got_frame;
         picture->pkt_dts = p->avpkt.dts;
-
-        if (p->result < 0)
-            err = p->result;
+        err = p->result;
 
         /*
          * A later call with avkpt->size == 0 may loop over all threads,
-         * including this one, searching for a frame to return before being
+         * including this one, searching for a frame/error to return before being
          * stopped by the "finished != fctx->next_finished" condition.
-         * Make sure we don't mistakenly return the same frame again.
+         * Make sure we don't mistakenly return the same frame/error again.
          */
         p->got_frame = 0;
+        p->result = 0;
 
         if (finished >= avctx->thread_count) finished = 0;
-    } while (!avpkt->size && !*got_picture_ptr && finished != fctx->next_finished);
+    } while (!avpkt->size && !*got_picture_ptr && err >= 0 && finished != fctx->next_finished);
 
     update_context_from_thread(avctx, p->avctx, 1);
 
-- 
2.9.3