lavc: do not implicitly share the frame pool between threads

Currently the frame pool used by the default get_buffer2()
implementation is a single struct, allocated when opening the decoder.
A pointer to it is simply copied to each frame thread and we assume that
no thread attempts to modify it at an unexpected time. This is rather
fragile and potentially dangerous.

With this commit, the frame pool is made refcounted, with the reference
being propagated across threads along with other context variables. The
frame pool is now also immutable - when the stream parameters change we
drop the old reference and create a new one.

1 files changed, 12 insertions, 0 deletions

diff --git a/libavcodec/pthread_frame.c b/libavcodec/pthread_frame.c
index f0a162bc92..4cd890b295 100644
--- a/libavcodec/pthread_frame.c
+++ b/libavcodec/pthread_frame.c
@@ -296,6 +296,17 @@ static int update_context_from_thread(AVCodecContext *dst, AVCodecContext *src,
         }
 
         dst->hwaccel_flags = src->hwaccel_flags;
+
+        if (!!dst->internal->pool != !!src->internal->pool ||
+            (dst->internal->pool && dst->internal->pool->data != src->internal->pool->data)) {
+            av_buffer_unref(&dst->internal->pool);
+
+            if (src->internal->pool) {
+                dst->internal->pool = av_buffer_ref(src->internal->pool);
+                if (!dst->internal->pool)
+                    return AVERROR(ENOMEM);
+            }
+        }
     }
 
     if (for_user) {
@@ -714,6 +725,7 @@ void ff_frame_thread_free(AVCodecContext *avctx, int thread_count)
         }
 
         if (p->avctx) {
+            av_buffer_unref(&p->avctx->internal->pool);
             av_freep(&p->avctx->internal);
             av_buffer_unref(&p->avctx->hw_frames_ctx);
         }