[libcamera-devel] [PATCH v4 4/4] android: camera_device: Send capture results by inspecting the queue

[Jacopo Mondi]

Hi Umang,

On Wed, Sep 29, 2021 at 07:00:30PM +0530, Umang Jain wrote:
> There is a possibility that an out-of-order completion of capture
> request happens by calling process_capture_result() directly on error
> paths. The framework expects that errors should be notified as soon as
> possible, but the request completion order should remain intact.
> An existing instance of this is abortRequest(), which sends the capture
> results on flushing state, without considering order-of-completion.
>
> Since we have a queue of Camera3RequestDescriptor tracking each
> capture request placed by framework to libcamera HAL, we should be only
> sending back capture results from a single location, by inspecting
> the queue. As per the patch, this now happens in
> CameraDevice::sendCaptureResults().
>
> Each descriptor is now equipped with its own status to denote whether
> the capture request is complete and ready to send back to the framework

ready to be sent

> or needs to be waited upon. This ensures that the order of completion is
> respected for the requests.
>
> Since we are fixing out-of-order request completion in abortRequest(),
> change the function to read from the Camera3RequestDescriptor directly,
> instead of camera3_capture_request_t. The descriptor should have all the
> information necessary to set the request buffers' state to error.
>
> Signed-off-by: Umang Jain <umang.jain at ideasonboard.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> Reviewed-by: Hirokazu Honda <hiroh at chromium.org>
> ---
>  src/android/camera_device.cpp | 59 ++++++++++++++++++++++++-----------
>  src/android/camera_device.h   | 14 ++++++++-
>  2 files changed, 54 insertions(+), 19 deletions(-)
>
> diff --git a/src/android/camera_device.cpp b/src/android/camera_device.cpp
> index 45350563..38c64bb7 100644
> --- a/src/android/camera_device.cpp
> +++ b/src/android/camera_device.cpp
> @@ -860,25 +860,25 @@ int CameraDevice::processControls(Camera3RequestDescriptor *descriptor)
>  	return 0;
>  }
>
> -void CameraDevice::abortRequest(camera3_capture_request_t *request) const
> +void CameraDevice::abortRequest(Camera3RequestDescriptor *descriptor) const
>  {
> -	notifyError(request->frame_number, nullptr, CAMERA3_MSG_ERROR_REQUEST);
> +	notifyError(descriptor->frameNumber_, nullptr, CAMERA3_MSG_ERROR_REQUEST);
>
> -	camera3_capture_result_t result = {};
> -	result.num_output_buffers = request->num_output_buffers;
> -	result.frame_number = request->frame_number;
> +	camera3_capture_result_t &result = descriptor->captureResult_;
> +	result.num_output_buffers = descriptor->buffers_.size();
> +	result.frame_number = descriptor->frameNumber_;
>  	result.partial_result = 0;
>
>  	std::vector<camera3_stream_buffer_t> resultBuffers(result.num_output_buffers);
>  	for (auto [i, buffer] : utils::enumerate(resultBuffers)) {
> -		buffer = request->output_buffers[i];
> -		buffer.release_fence = request->output_buffers[i].acquire_fence;
> +		buffer = descriptor->buffers_[i];
> +		buffer.release_fence = descriptor->buffers_[i].acquire_fence;
>  		buffer.acquire_fence = -1;
>  		buffer.status = CAMERA3_BUFFER_STATUS_ERROR;
>  	}
>  	result.output_buffers = resultBuffers.data();
>
> -	callbacks_->process_capture_result(callbacks_, &result);
> +	descriptor->status_ = Camera3RequestDescriptor::Status::Error;
>  }
>
>  bool CameraDevice::isValidRequest(camera3_capture_request_t *camera3Request) const
> @@ -1050,13 +1050,21 @@ int CameraDevice::processCaptureRequest(camera3_capture_request_t *camera3Reques
>  		return ret;
>
>  	/*
> -	 * If flush is in progress abort the request. If the camera has been
> -	 * stopped we have to re-start it to be able to process the request.
> +	 * If flush is in progress set the request status to error and place it
> +	 * on the queue to be later completed. If the camera has been stopped we
> +	 * have to re-start it to be able to process the request.
>  	 */
>  	MutexLocker stateLock(stateMutex_);
>
>  	if (state_ == State::Flushing) {
> -		abortRequest(camera3Request);
> +		abortRequest(descriptor.get());
> +		{
> +			MutexLocker descriptorsLock(descriptorsMutex_);
> +			descriptors_.push(std::move(descriptor));
> +		}
> +
> +		sendCaptureResults();
> +
>  		return 0;
>  	}
>
> @@ -1116,7 +1124,7 @@ void CameraDevice::requestComplete(Request *request)
>  	 * The buffer status is set to OK and later changed to ERROR if
>  	 * post-processing/compression fails.
>  	 */
> -	camera3_capture_result_t captureResult = {};
> +	camera3_capture_result_t &captureResult = descriptor->captureResult_;
>  	captureResult.frame_number = descriptor->frameNumber_;
>  	captureResult.num_output_buffers = descriptor->buffers_.size();
>  	for (camera3_stream_buffer_t &buffer : descriptor->buffers_) {
> @@ -1166,10 +1174,9 @@ void CameraDevice::requestComplete(Request *request)
>  			buffer.status = CAMERA3_BUFFER_STATUS_ERROR;
>  		}
>
> -		callbacks_->process_capture_result(callbacks_, &captureResult);
> +		descriptor->status_ = Camera3RequestDescriptor::Status::Error;
> +		sendCaptureResults();
>
> -		MutexLocker descriptorsLock(descriptorsMutex_);
> -		descriptors_.pop();
>  		return;
>  	}
>
> @@ -1235,10 +1242,26 @@ void CameraDevice::requestComplete(Request *request)
>  	}
>
>  	captureResult.result = resultMetadata->get();
> -	callbacks_->process_capture_result(callbacks_, &captureResult);
> +	descriptor->status_ = Camera3RequestDescriptor::Status::Success;
> +	sendCaptureResults();
> +}
>
> -	MutexLocker descriptorsLock(descriptorsMutex_);
> -	descriptors_.pop();
> +void CameraDevice::sendCaptureResults()
> +{
> +	MutexLocker lock(descriptorsMutex_);
> +	while (!descriptors_.empty() && !descriptors_.front()->isPending()) {
> +		auto descriptor = std::move(descriptors_.front());
> +		descriptors_.pop();
> +
> +		/*
> +		 * \todo Measure performance impact of grain locking here against
> +		 * coarse locking.

I find this a bit hard to parse. Maybe

		 * \todo Releasing and re-acquiring the critical
                 * section for every request completion might have an
                 * impact on performaces which should be measured.

Up to you, really.

All minors might be optionally fixed when applying

Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>

> +		 */
> +		lock.unlock();
> +		callbacks_->process_capture_result(callbacks_,
> +						   &descriptor->captureResult_);
> +		lock.lock();
> +	}
>  }
>
>  std::string CameraDevice::logPrefix() const
> diff --git a/src/android/camera_device.h b/src/android/camera_device.h
> index 85497921..b7d774fe 100644
> --- a/src/android/camera_device.h
> +++ b/src/android/camera_device.h
> @@ -74,17 +74,28 @@ private:
>  	CameraDevice(unsigned int id, std::shared_ptr<libcamera::Camera> camera);
>
>  	struct Camera3RequestDescriptor {
> +		enum class Status {
> +			Pending,
> +			Success,
> +			Error,
> +		};
> +
>  		Camera3RequestDescriptor() = default;
>  		~Camera3RequestDescriptor() = default;
>  		Camera3RequestDescriptor(libcamera::Camera *camera,
>  					 const camera3_capture_request_t *camera3Request);
>  		Camera3RequestDescriptor &operator=(Camera3RequestDescriptor &&) = default;
>
> +		bool isPending() const { return status_ == Status::Pending; }
> +
>  		uint32_t frameNumber_ = 0;
>  		std::vector<camera3_stream_buffer_t> buffers_;
>  		std::vector<std::unique_ptr<libcamera::FrameBuffer>> frameBuffers_;
>  		CameraMetadata settings_;
>  		std::unique_ptr<CaptureRequest> request_;
> +
> +		camera3_capture_result_t captureResult_ = {};
> +		Status status_ = Status::Pending;
>  	};
>
>  	enum class State {
> @@ -99,12 +110,13 @@ private:
>  	createFrameBuffer(const buffer_handle_t camera3buffer,
>  			  libcamera::PixelFormat pixelFormat,
>  			  const libcamera::Size &size);
> -	void abortRequest(camera3_capture_request_t *request) const;
> +	void abortRequest(Camera3RequestDescriptor *descriptor) const;
>  	bool isValidRequest(camera3_capture_request_t *request) const;
>  	void notifyShutter(uint32_t frameNumber, uint64_t timestamp);
>  	void notifyError(uint32_t frameNumber, camera3_stream_t *stream,
>  			 camera3_error_msg_code code) const;
>  	int processControls(Camera3RequestDescriptor *descriptor);
> +	void sendCaptureResults();
>  	std::unique_ptr<CameraMetadata> getResultMetadata(
>  		const Camera3RequestDescriptor &descriptor) const;
>
> --
> 2.31.0
>