potential concurrency issue in encoder

[bmegli]

Short Description

• User's FFmpeg encode2
• Nvidia's DQThread through capture plane callback

Are accessing same data without thread synchronization.

[bmegli]

Long Description

Dequeue Thread

Dequeue thread working through encoder_capture_plane_dq_callback

jetson-ffmpeg/nvmpi_enc.cpp

Lines 354 to 356 in 2006718

	ctx->enc->capture_plane.setDQThreadCallback(encoder_capture_plane_dq_callback);
	ctx->enc->capture_plane.startDQThread(ctx);

Touching packet_pools

jetson-ffmpeg/nvmpi_enc.cpp

Line 90 in 2006718

ctx->packet_pools->push(ctx->buf_index);

User's Thread through FFmpeg

FFmpeg encode2

jetson-ffmpeg/ffmpeg_nvmpi.patch

Line 630 in 2006718

+ .encode2 = nvmpi_encode_frame, \

tapping into nvmpi_encode_frame

jetson-ffmpeg/ffmpeg_nvmpi.patch

Line 526 in 2006718

+ if(nvmpi_encoder_get_packet(nvmpi_context->ctx,&packet)<0)

Tapping into packet_pools

jetson-ffmpeg/nvmpi_enc.cpp

Line 431 in 2006718

packet_index= ctx->packet_pools->front();

Consequence

Two threads may access at least packet_pools concurrently (push, pop, front, consuming the data)

[bmegli]

This currently doesn't have much impact due to other side effect of jetson-ffmpeg implementation.

More on that in other issue.