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avcodec/pthread_frame: Don't update the first thread ctx before freeing

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Currently, ff_frame_thread_free() uses the last worker thread
to updates the first worker thread via update_context_from_thread()
immediately before freeing all these worker threads. This is
a remnant of the time in which the first worker was special.
(E.g. the first worker shared its AVCodecInternal with the public
AVCodecContext.)

But these times are over (none of the uses of is_copy matter
for ff_frame_thread_free()); nowadays the only thing that
update_context_from_thread() does is referencing a few
buffers/frames and replacing them with other references instead.
These new references will then be freed immediately thereafter
when the first worker thread is freed. Ensuring that the code is
free of double-frees is achieved by using reference-counted structures
(or in case of AVChannelLayouts: by giving each worker its own copy).

Some archaeology:
a) Updating the first worker thread from the last one used
has been done since frame-threading was added in
37b00b47cb.
b) The precursor to ff_mpv_common_end() checked for is_copy
before freeing pictures (i.e. it only freed them for the first
worker thread).
c) Commits c2dfb1e37c and
e33811bd26 modified the
update_thread_context function of the H.264 decoder
so that it could fail before calling ff_mpeg_update_thread_context().
d) This led to a double free/an assert violation with a H.264
sample for which ff_mpeg_update_thread_context() is not reached
for the final update_context_from_thread(). Commit
a6e4796fbf added code to fix this
sample.
e) This issue was fixed (even with the last mentioned commit reverted)
when the H.264 decoder was deMpegEncContextized in commit
b7fe35c9e5 (merging commit
2c54155407).
f) mpegvideo.c stopped using is_copy when it was switched to refcounted
frames in 759001c534.
g) 1f4cf92cfb removed the init_thread_copy
callbacks; now no FFCodec.close callback checks for is_copy at all
any more.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt 2022-05-18 22:50:38 +02:00
parent a78173374a
commit 49838705a4
1 changed files with 0 additions and 7 deletions
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7
libavcodec/pthread_frame.c
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@ -714,13 +714,6 @@ void ff_frame_thread_free(AVCodecContext *avctx, int thread_count)
}
}
if (fctx->prev_thread && fctx->prev_thread != fctx->threads)
if (update_context_from_thread(fctx->threads->avctx, fctx->prev_thread->avctx, 0) < 0) {
av_log(avctx, AV_LOG_ERROR, "Final thread update failed\n");
fctx->prev_thread->avctx->internal->is_copy = fctx->threads->avctx->internal->is_copy;
fctx->threads->avctx->internal->is_copy = 1;
}
for (i = 0; i < thread_count; i++) {
PerThreadContext *p = &fctx->threads[i];
AVCodecContext *ctx = p->avctx;