[libcamera-devel] [PATCH v1 4/6] android: camera_device: Add a queue for sending capture results

[Kieran Bingham]

On 07/09/2021 20:57, Umang Jain wrote:
> When a camera capture request completes, the next step is to send the
> capture results to the framework via process_capture_results(). All
> the capture associated result metadata is prepared and populated. If
> any post-processing is required, it will also take place in the same
> thread (which can be blocking for a subtaintial amount of time) before

s/subtaintial/substantial/


> the results can be sent back to the framework.
> 
> A follow up commit will move the post-processing to run in a separate
> thread. In order to do so, there is few bits of groundwork which this
> patch entails. Mainly, we need to preserve the order of sending
> the capture results back in which they were queued by the framework
> to the HAL (i.e. the order is sequential). Hence, we need to add a queue
> in which capture results can be queued with context.
> 
> As per this patch, the post-processor still runs synchronously as
> before, but it will queue up the current capture results with context.
> Later down the line, the capture results are dequeud in order and

s/dequeud/dequeued/


> sent back to the framework.
> 
> The context is preserved using Camera3RequestDescriptor utility
> structure. It has been expanded accordingly to address the needs of
> the functionality.
> 
> Signed-off-by: Umang Jain <umang.jain at ideasonboard.com>
> ---
>  src/android/camera_device.cpp | 113 +++++++++++++++++++++++++++++++---
>  src/android/camera_device.h   |  23 +++++++
>  2 files changed, 126 insertions(+), 10 deletions(-)
> 
> diff --git a/src/android/camera_device.cpp b/src/android/camera_device.cpp
> index f2f36f32..9d4ec02e 100644
> --- a/src/android/camera_device.cpp
> +++ b/src/android/camera_device.cpp
> @@ -240,6 +240,8 @@ CameraDevice::Camera3RequestDescriptor::Camera3RequestDescriptor(
>  	/* Clone the controls associated with the camera3 request. */
>  	settings_ = CameraMetadata(camera3Request->settings);
>  
> +	internalBuffer_ = nullptr;
> +
>  	/*
>  	 * Create the CaptureRequest, stored as a unique_ptr<> to tie its
>  	 * lifetime to the descriptor.
> @@ -989,6 +991,7 @@ int CameraDevice::processCaptureRequest(camera3_capture_request_t *camera3Reques
>  			 * once it has been processed.
>  			 */
>  			buffer = cameraStream->getBuffer();
> +			descriptor.internalBuffer_ = buffer;
>  			LOG(HAL, Debug) << ss.str() << " (internal)";
>  			break;
>  		}
> @@ -1148,25 +1151,115 @@ void CameraDevice::requestComplete(Request *request)
>  			continue;
>  		}
>  
> +		/*
> +		 * Save the current context of capture result and queue the
> +		 * descriptor before processing the camera stream.
> +		 *
> +		 * When the processing completes, the descriptor will be
> +		 * dequeued and capture results will be sent to the framework.
> +		 */
> +		descriptor.status_ = Camera3RequestDescriptor::NOT_FINISHED;
> +		descriptor.resultMetadata_ = std::move(resultMetadata);
> +		descriptor.captureResult_ = captureResult;
> +
> +		std::unique_ptr<Camera3RequestDescriptor> reqDescriptor =
> +			std::make_unique<Camera3RequestDescriptor>();
> +		*reqDescriptor = std::move(descriptor);
> +		queuedDescriptor_.push_back(std::move(reqDescriptor));
> +		Camera3RequestDescriptor *currentDescriptor = queuedDescriptor_.back().get();
> +
> +		CameraMetadata *metadata = currentDescriptor->resultMetadata_.get();
> +		cameraStream->processComplete.connect(
> +			this, [=](CameraStream::ProcessStatus status) {
> +				streamProcessingComplete(cameraStream, status,
> +							 metadata);

I believe this to be unsafe to manage multiple operations.

cameraStream->processComplete() should not be connected with per-run
parameters. Those should be passed as the context of the signal emit(),
not by the connection.

Otherwise, the lamba will be overwritten by the next requestComplete()
and incorrect parameters will be processed when the signal actually fires.



> +			});
> +
>  		int ret = cameraStream->process(src, *buffer.buffer,
> -						descriptor.settings_,
> -						resultMetadata.get());
> +						currentDescriptor->settings_,
> +						metadata);
> +		return;
> +	}
> +
> +	if (queuedDescriptor_.empty()) {
> +		captureResult.result = resultMetadata->get();
> +		callbacks_->process_capture_result(callbacks_, &captureResult);

*1 duplication of completion callbacks (see below)


> +	} else {
> +		/*
> +		 * Previous capture results waiting to be sent to framework
> +		 * hence, queue the current capture results as well. After that,
> +		 * check if any results are ready to be sent back to the
> +		 * framework.
> +		 */
> +		descriptor.status_ = Camera3RequestDescriptor::FINISHED_SUCCESS;
> +		descriptor.resultMetadata_ = std::move(resultMetadata);
> +		descriptor.captureResult_ = captureResult;
> +		std::unique_ptr<Camera3RequestDescriptor> reqDescriptor =
> +			std::make_unique<Camera3RequestDescriptor>();
> +		*reqDescriptor = std::move(descriptor);
> +		queuedDescriptor_.push_back(std::move(reqDescriptor));
> +
> +		sendQueuedCaptureResults();
> +	}
> +}
> +
> +void CameraDevice::streamProcessingComplete(CameraStream *cameraStream,
> +					    CameraStream::ProcessStatus status,
> +					    CameraMetadata *resultMetadata)
> +{
> +	for (auto &d : queuedDescriptor_) {
> +		if (d->resultMetadata_.get() != resultMetadata)
> +			continue;
> +
>  		/*
>  		 * Return the FrameBuffer to the CameraStream now that we're
>  		 * done processing it.
>  		 */
>  		if (cameraStream->type() == CameraStream::Type::Internal)
> -			cameraStream->putBuffer(src);
> -
> -		if (ret) {
> -			buffer.status = CAMERA3_BUFFER_STATUS_ERROR;
> -			notifyError(descriptor.frameNumber_, buffer.stream,
> -				    CAMERA3_MSG_ERROR_BUFFER);
> +			cameraStream->putBuffer(d->internalBuffer_);
> +
> +		if (status == CameraStream::ProcessStatus::Success) {
> +			d->status_ = Camera3RequestDescriptor::FINISHED_SUCCESS;
> +		} else {
> +			d->status_ = Camera3RequestDescriptor::FINISHED_FAILED;
> +			d->captureResult_.partial_result = 0;
> +			for (camera3_stream_buffer_t &buffer : d->buffers_) {
> +				CameraStream *cs = static_cast<CameraStream *>(buffer.stream->priv);
> +
> +				if (cs->camera3Stream().format != HAL_PIXEL_FORMAT_BLOB)
> +					continue;
> +
> +				buffer.status = CAMERA3_BUFFER_STATUS_ERROR;
> +				notifyError(d->frameNumber_, buffer.stream,
> +					    CAMERA3_MSG_ERROR_BUFFER);
> +			}
>  		}
> +
> +		break;
>  	}
>  
> -	captureResult.result = resultMetadata->get();
> -	callbacks_->process_capture_result(callbacks_, &captureResult);
> +	/*
> +	 * Send back capture results to the framework by inspecting the queue.
> +	 * The framework can defer queueing further requests to the HAL (via
> +	 * process_capture_request) unless until it receives the capture results
> +	 * for already queued requests.
> +	 */
> +	sendQueuedCaptureResults();
> +}
> +
> +void CameraDevice::sendQueuedCaptureResults()
> +{
> +	while (!queuedDescriptor_.empty()) {
> +		std::unique_ptr<Camera3RequestDescriptor> &d = queuedDescriptor_.front();

I'd have this exit early if the front descriptor is not finished.


> +		if (d->status_ != Camera3RequestDescriptor::NOT_FINISHED) {
> +			d->captureResult_.result = d->resultMetadata_->get();
> +			callbacks_->process_capture_result(callbacks_,
> +							   &(d->captureResult_));

Not as part of this patch, but I feel like Camera3RequestDescriptor
could have a method called complete() to wrap the management of the
completion against a request descriptor.

There's lots of occasions where the metadata is obtained or processed
into a result structure and called back with a flag.

(such as *1 above, but I think there are more)

It seems to me like that could be made into

		d->complete(CameraRequest::Success);

or something.... But that's an overall design of breaking out the
Camera3RequestDescriptor to a full class.

As this series is extending Camera3RequestDescriptor to maintain extra
state required for the asynchronous post-processing, that makes me think
it would be better to have a full class to manage that state. (and thus
methods to operate on it)·



> +			queuedDescriptor_.pop_front();
> +		} else {
> +			break;
> +		}
> +	}
>  }
>  
>  std::string CameraDevice::logPrefix() const
> diff --git a/src/android/camera_device.h b/src/android/camera_device.h
> index a5576927..36425773 100644
> --- a/src/android/camera_device.h
> +++ b/src/android/camera_device.h
> @@ -7,6 +7,7 @@
>  #ifndef __ANDROID_CAMERA_DEVICE_H__
>  #define __ANDROID_CAMERA_DEVICE_H__
>  
> +#include <deque>
>  #include <map>
>  #include <memory>
>  #include <mutex>
> @@ -83,6 +84,21 @@ private:
>  		std::vector<std::unique_ptr<libcamera::FrameBuffer>> frameBuffers_;
>  		CameraMetadata settings_;
>  		std::unique_ptr<CaptureRequest> request_;
> +
> +		/*
> +		 * Below are utility placeholders used when a capture result
> +		 * needs to be queued before completion via
> +		 * process_capture_result() callback.
> +		 */
> +		enum completionStatus {
> +			NOT_FINISHED,

I'd call this "Active" or "Pending" to reduce the negation...

	"If (state == Active)"
rather than
	"if (state != NOT_FINISHED)"


> +			FINISHED_SUCCESS,

I'd call this Success or Succeeded, or Successful ..

> +			FINISHED_FAILED,

And Failed



> +		};
> +		std::unique_ptr<CameraMetadata> resultMetadata_;
> +		camera3_capture_result_t captureResult_;
> +		libcamera::FrameBuffer *internalBuffer_;
> +		completionStatus status_;

These are all used to track the post-processor context.




>  	};
>  
>  	enum class State {
> @@ -105,6 +121,11 @@ private:
>  	std::unique_ptr<CameraMetadata> getResultMetadata(
>  		const Camera3RequestDescriptor &descriptor) const;
>  
> +	void sendQueuedCaptureResults();
> +	void streamProcessingComplete(CameraStream *stream,
> +				      CameraStream::ProcessStatus status,
> +				      CameraMetadata *resultMetadata);
> +
>  	unsigned int id_;
>  	camera3_device_t camera3Device_;
>  
> @@ -125,6 +146,8 @@ private:
>  	libcamera::Mutex descriptorsMutex_; /* Protects descriptors_. */
>  	std::map<uint64_t, Camera3RequestDescriptor> descriptors_;
>  
> +	std::deque<std::unique_ptr<Camera3RequestDescriptor>> queuedDescriptor_;

I'm not yet sure if this should be a unique_ptr ..


> +
>  	std::string maker_;
>  	std::string model_;
>  
>