Apr 22, 2023, 14:42 by an...@khirnov.net: > Quoting Lynne (2023-04-19 16:39:28) > >> Apr 17, 2023, 11:25 by an...@khirnov.net: >> >> > Quoting Lynne (2023-03-14 07:33:43) >> > >> >> From 6e2dfc44e50798264eb16bc2dcabfdbf2fbac2d7 Mon Sep 17 00:00:00 2001 >> >> From: Lynne <d...@lynne.ee> >> >> Date: Thu, 15 Dec 2022 01:06:52 +0100 >> >> Subject: [PATCH 24/92] hwconfig: add a new HWACCEL_CAP_THREAD_SAFE for >> >> threadsafe hwaccels >> >> >> >> Vulkan is fully threadsafe and stateless, so we can benefit from this. >> >> --- >> >> libavcodec/hwconfig.h | 1 + >> >> libavcodec/pthread_frame.c | 2 +- >> >> 2 files changed, 2 insertions(+), 1 deletion(-) >> >> >> >> diff --git a/libavcodec/hwconfig.h b/libavcodec/hwconfig.h >> >> index 721424912c..e6b78f0160 100644 >> >> --- a/libavcodec/hwconfig.h >> >> +++ b/libavcodec/hwconfig.h >> >> @@ -24,6 +24,7 @@ >> >> >> >> >> >> #define HWACCEL_CAP_ASYNC_SAFE (1 << 0) >> >> +#define HWACCEL_CAP_THREAD_SAFE (1 << 1) >> >> >> >> >> >> typedef struct AVCodecHWConfigInternal { >> >> diff --git a/libavcodec/pthread_frame.c b/libavcodec/pthread_frame.c >> >> index 74864e19c5..c096287233 100644 >> >> --- a/libavcodec/pthread_frame.c >> >> +++ b/libavcodec/pthread_frame.c >> >> @@ -204,7 +204,7 @@ static attribute_align_arg void >> >> *frame_worker_thread(void *arg) >> >> >> >> /* if the previous thread uses hwaccel then we take the lock to ensure >> >> * the threads don't run concurrently */ >> >> - if (avctx->hwaccel) { >> >> + if (avctx->hwaccel && !(avctx->hwaccel->caps_internal & >> >> HWACCEL_CAP_THREAD_SAFE)) { >> >> >> > >> > A major problem here is that hwaccel_priv_data exists in only a single >> > instance shared across all the worker threads. If you want frame-threaded >> > hwaccels, you'll need to add some mechanism for synchronizing it between >> > threads. >> > >> > I really wonder how does your code survive all the races involved. >> > >> >> It works because hwaccel_priv_data is read-only. No need to synchronize >> anything, the contexts Vulkan creates are defined as driver-synchronized, >> and all the info a frame needs is provided when decoding it, rather than >> kept as a state. >> So I don't see a problem here. >> > > From a quick glance, at least vk_av1_free_frame_priv() modifies this > context, which seems highly unsafe. >
Our AV1 decoder isn't threaded yet. I've removed the threadsafe flag from the hwaccel, Dave is currently looking into whether it's possible to remove the frame id. > This really seems like a disaster waiting to happen, there should be > some stronger guarantees that nobody will modify this context when they > shouldn't. > It's an opt-in flag, that's more than enough. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".