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From: Anton Khirnov <anton@khirnov.net>
To: ffmpeg-devel@ffmpeg.org
Date: Sat, 3 Sep 2022 20:39:30 +0200
Message-Id: <20220903183930.9223-2-anton@khirnov.net>
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<20220903183930.9223-1-anton@khirnov.net>
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Subject: [FFmpeg-devel] [PATCH 2/2] lavc/pthread_frame: avoid leaving stale
hwaccel state in worker threads
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This state is not refcounted, so make sure it always has a well-defined
owner.
Remove the block added in 091341f2ab5bd35ca1a2aae90503adc74f8d3523, as
this commit also solves that issue in a more general way.
---
libavcodec/pthread_frame.c | 47 ++++++++++++++++++++++++++++----------
1 file changed, 35 insertions(+), 12 deletions(-)
diff --git a/libavcodec/pthread_frame.c b/libavcodec/pthread_frame.c
index 08a6f98898..066269621d 100644
--- a/libavcodec/pthread_frame.c
+++ b/libavcodec/pthread_frame.c
@@ -148,6 +148,12 @@ typedef struct FrameThreadContext {
* Set for the first N packets, where N is the number of threads.
* While it is set, ff_thread_en/decode_frame won't return any results.
*/
+
+ /* hwaccel state is temporarily stored here in order to transfer its ownership
+ * to the next decoding thread without the need for extra synchronization */
+ const AVHWAccel *stash_hwaccel;
+ void *stash_hwaccel_context;
+ void *stash_hwaccel_priv;
} FrameThreadContext;
#if FF_API_THREAD_SAFE_CALLBACKS
@@ -228,9 +234,17 @@ FF_ENABLE_DEPRECATION_WARNINGS
ff_thread_finish_setup(avctx);
if (p->hwaccel_serializing) {
+ /* wipe hwaccel state to avoid stale pointers lying around;
+ * the state was transferred to FrameThreadContext in
+ * ff_thread_finish_setup(), so nothing is leaked */
+ avctx->hwaccel = NULL;
+ avctx->hwaccel_context = NULL;
+ avctx->internal->hwaccel_priv_data = NULL;
+
p->hwaccel_serializing = 0;
pthread_mutex_unlock(&p->parent->hwaccel_mutex);
}
+ av_assert0(!avctx->hwaccel);
if (p->async_serializing) {
p->async_serializing = 0;
@@ -294,9 +308,6 @@ static int update_context_from_thread(AVCodecContext *dst, AVCodecContext *src,
dst->color_range = src->color_range;
dst->chroma_sample_location = src->chroma_sample_location;
- dst->hwaccel = src->hwaccel;
- dst->hwaccel_context = src->hwaccel_context;
-
dst->sample_rate = src->sample_rate;
dst->sample_fmt = src->sample_fmt;
#if FF_API_OLD_CHANNEL_LAYOUT
@@ -309,8 +320,6 @@ FF_ENABLE_DEPRECATION_WARNINGS
if (err < 0)
return err;
- dst->internal->hwaccel_priv_data = src->internal->hwaccel_priv_data;
-
if (!!dst->hw_frames_ctx != !!src->hw_frames_ctx ||
(dst->hw_frames_ctx && dst->hw_frames_ctx->data != src->hw_frames_ctx->data)) {
av_buffer_unref(&dst->hw_frames_ctx);
@@ -450,6 +459,12 @@ static int submit_packet(PerThreadContext *p, AVCodecContext *user_avctx,
pthread_mutex_unlock(&p->mutex);
return err;
}
+
+ /* transfer hwaccel state stashed from previous thread, if any */
+ av_assert0(!p->avctx->hwaccel);
+ FFSWAP(const AVHWAccel*, p->avctx->hwaccel, fctx->stash_hwaccel);
+ FFSWAP(void*, p->avctx->hwaccel_context, fctx->stash_hwaccel_context);
+ FFSWAP(void*, p->avctx->internal->hwaccel_priv_data, fctx->stash_hwaccel_priv);
}
av_packet_unref(p->avpkt);
@@ -655,6 +670,14 @@ void ff_thread_finish_setup(AVCodecContext *avctx) {
async_lock(p->parent);
}
+ /* save hwaccel state for passing to the next thread;
+ * this is done here so that this worker thread can wipe its own hwaccel
+ * state after decoding, without requiring synchronization */
+ av_assert0(!p->parent->stash_hwaccel);
+ p->parent->stash_hwaccel = avctx->hwaccel;
+ p->parent->stash_hwaccel_context = avctx->hwaccel_context;
+ p->parent->stash_hwaccel_priv = avctx->internal->hwaccel_priv_data;
+
pthread_mutex_lock(&p->progress_mutex);
if(atomic_load(&p->state) == STATE_SETUP_FINISHED){
av_log(avctx, AV_LOG_WARNING, "Multiple ff_thread_finish_setup() calls\n");
@@ -708,13 +731,6 @@ void ff_frame_thread_free(AVCodecContext *avctx, int thread_count)
park_frame_worker_threads(fctx, thread_count);
- if (fctx->prev_thread && avctx->internal->hwaccel_priv_data !=
- fctx->prev_thread->avctx->internal->hwaccel_priv_data) {
- if (update_context_from_thread(avctx, fctx->prev_thread->avctx, 1) < 0) {
- av_log(avctx, AV_LOG_ERROR, "Failed to update user thread.\n");
- }
- }
-
for (i = 0; i < thread_count; i++) {
PerThreadContext *p = &fctx->threads[i];
AVCodecContext *ctx = p->avctx;
@@ -761,6 +777,13 @@ void ff_frame_thread_free(AVCodecContext *avctx, int thread_count)
av_freep(&fctx->threads);
ff_pthread_free(fctx, thread_ctx_offsets);
+ /* if we have stashed hwaccel state, move it to the user-facing context,
+ * so it will be freed in avcodec_close() */
+ av_assert0(!avctx->hwaccel);
+ FFSWAP(const AVHWAccel*, avctx->hwaccel, fctx->stash_hwaccel);
+ FFSWAP(void*, avctx->hwaccel_context, fctx->stash_hwaccel_context);
+ FFSWAP(void*, avctx->internal->hwaccel_priv_data, fctx->stash_hwaccel_priv);
+
av_freep(&avctx->internal->thread_ctx);
}
--
2.35.1
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