[libcamera-devel,v5,1/4] android: Notify post processing completion via a signal

14189 diff mbox series

Notify that the post processing for a request has been completed,
via a signal. A pointer to the descriptor which is tracking the
capture request is emitted along with the status of post processed
buffer. The function CameraDevice::streamProcessingComplete() will
finally set the status on the request descriptor and send capture
results back to the framework accordingly.

We also need to save a pointer to any internal buffers that might have
been allocated by CameraStream. The buffer should be returned back to
CameraStream just before capture results are sent.

A streamProcessMutex_ has been introduced here itself, which will be
applicable to guard access to descriptor->buffers_ when post-processing
is moved to be asynchronous in subsequent commits.

Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
---
 src/android/camera_device.cpp            | 92 +++++++++++++++++++++---
 src/android/camera_device.h              |  7 ++
 src/android/camera_request.h             |  4 ++
 src/android/camera_stream.cpp            | 13 ++++
 src/android/jpeg/post_processor_jpeg.cpp |  2 +
 src/android/post_processor.h             |  9 +++
 src/android/yuv/post_processor_yuv.cpp   | 10 ++-
 7 files changed, 125 insertions(+), 12 deletions(-)

Hi Umang,

Thank you for the patch.

On Wed, Oct 20, 2021 at 04:12:09PM +0530, Umang Jain wrote:
> Notify that the post processing for a request has been completed,
> via a signal. A pointer to the descriptor which is tracking the
> capture request is emitted along with the status of post processed
> buffer. The function CameraDevice::streamProcessingComplete() will
> finally set the status on the request descriptor and send capture
> results back to the framework accordingly.
> 
> We also need to save a pointer to any internal buffers that might have
> been allocated by CameraStream. The buffer should be returned back to
> CameraStream just before capture results are sent.
> 
> A streamProcessMutex_ has been introduced here itself, which will be

Did you mean s/itself/as well/ ?

> applicable to guard access to descriptor->buffers_ when post-processing
> is moved to be asynchronous in subsequent commits.
> 
> Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
> ---
>  src/android/camera_device.cpp            | 92 +++++++++++++++++++++---
>  src/android/camera_device.h              |  7 ++
>  src/android/camera_request.h             |  4 ++
>  src/android/camera_stream.cpp            | 13 ++++
>  src/android/jpeg/post_processor_jpeg.cpp |  2 +
>  src/android/post_processor.h             |  9 +++
>  src/android/yuv/post_processor_yuv.cpp   | 10 ++-
>  7 files changed, 125 insertions(+), 12 deletions(-)
> 
> diff --git a/src/android/camera_device.cpp b/src/android/camera_device.cpp
> index 806b4090..541c2c81 100644
> --- a/src/android/camera_device.cpp
> +++ b/src/android/camera_device.cpp
> @@ -1117,6 +1117,15 @@ void CameraDevice::requestComplete(Request *request)
>  	}
>  
>  	/* Handle post-processing. */
> +	bool needsPostProcessing = false;
> +	Camera3RequestDescriptor::Status processingStatus =
> +		Camera3RequestDescriptor::Status::Pending;
> +	/*
> +	 * \todo Apply streamsProcessMutex_ when post-processing is adapted to run
> +	 * asynchronously. If we introduce the streamsProcessMutex_ right away, the
> +	 * lock will be held forever since it is synchronous at this point
> +	 * (see streamProcessingComplete).
> +	 */
>  	for (auto &buffer : descriptor->buffers_) {
>  		CameraStream *stream = buffer.stream;
>  
> @@ -1132,22 +1141,27 @@ void CameraDevice::requestComplete(Request *request)
>  			continue;
>  		}
>  
> -		int ret = stream->process(*src, buffer, descriptor);
> -
> -		/*
> -		 * Return the FrameBuffer to the CameraStream now that we're
> -		 * done processing it.
> -		 */
>  		if (stream->type() == CameraStream::Type::Internal)
> -			stream->putBuffer(src);
> +			buffer.internalBuffer = src;

Let's make the field name more self-explanatory. A possible candidate is
sourceBuffer instead of internalBuffer.

Could we do this in CameraDevice::processCaptureRequest(), just after
calling cameraStream->getBuffer() ? I'll feel less worried about a leak
if we store the buffer for later release right after acquiring it.

>  
> +		needsPostProcessing = true;
> +		int ret = stream->process(*src, buffer, descriptor);
>  		if (ret) {
> -			buffer.status = Camera3RequestDescriptor::Status::Error;
> -			notifyError(descriptor->frameNumber_, stream->camera3Stream(),
> -				    CAMERA3_MSG_ERROR_BUFFER);
> +			setBufferStatus(stream, buffer, descriptor,
> +					Camera3RequestDescriptor::Status::Error);
> +			processingStatus = Camera3RequestDescriptor::Status::Error;
>  		}

I think we need to improve error handling a little bit, in order to
support multiple streams being post-processed. We need to complete the
request in CameraDevice::streamProcessingComplete() when the last
processing stream completes, so the number of post-processed streams
need to be somehow recorded in the Camera3RequestDescriptor. It could be
tempted to have a counter, but a

	std::map<CameraStream *, StreamBuffer *> pendingPostProcess_;

could be better, as it will also remove the need for loops in
streamProcessingComplete() to lookup the buffer from the stream and to
check if the request has been fully processed. Accessing the map has to
be done with the mutex held to avoid race conditions, but it's a bit
more tricky than that. If we just add elements to the map here, we could
race with streamProcessingComplete() as it could be called for the first
post-processed stream before we have a chance to add the second one
here. streamProcessingComplete() would then incorrectly think it has
completed the last stream, and proceed to complete the request.

This race could be solved by holding the lock for the whole duration of
the loop here, covering all calls to stream->process(), but it may be
possible to do better. We could add entries to the map in
processCaptureRequest() instead. We would need, here, to remove entries
from the map if stream->process() fails, and complete the request if we
remove the last entry (as otherwise, streamProcessingComplete() could
complete all streams, then the last stream->process() call could fail,
and nobody would complete the request).

Other designs may be possible.

>  	}
>  
> +	if (needsPostProcessing) {
> +		if (processingStatus == Camera3RequestDescriptor::Status::Error) {
> +			descriptor->status_ = processingStatus;
> +			sendCaptureResults();
> +		}
> +
> +		return;
> +	}
> +
>  	descriptor->status_ = Camera3RequestDescriptor::Status::Success;
>  	sendCaptureResults();
>  }
> @@ -1206,6 +1220,64 @@ void CameraDevice::sendCaptureResults()
>  	}
>  }
>  
> +void CameraDevice::setBufferStatus(CameraStream *cameraStream,
> +				   Camera3RequestDescriptor::StreamBuffer &buffer,
> +				   Camera3RequestDescriptor *request,
> +				   Camera3RequestDescriptor::Status status)
> +{
> +	/*
> +	 * Return the FrameBuffer to the CameraStream now that we're
> +	 * done processing it.
> +	 */
> +	if (cameraStream->type() == CameraStream::Type::Internal)
> +		cameraStream->putBuffer(buffer.internalBuffer);
> +
> +	buffer.status = status;
> +	if (status != Camera3RequestDescriptor::Status::Success)
> +		notifyError(request->frameNumber_, buffer.stream->camera3Stream(),
> +			    CAMERA3_MSG_ERROR_BUFFER);
> +}
> +
> +void CameraDevice::streamProcessingComplete(CameraStream *cameraStream,
> +					    Camera3RequestDescriptor *request,
> +					    Camera3RequestDescriptor::Status status)
> +{
> +	MutexLocker locker(request->streamsProcessMutex_);
> +	for (auto &buffer : request->buffers_) {
> +		if (buffer.stream != cameraStream)
> +			continue;
> +
> +		setBufferStatus(cameraStream, buffer, request, status);
> +	}
> +
> +	bool hasPostProcessingErrors = false;
> +	for (auto &buffer : request->buffers_) {
> +		if (cameraStream->type() == CameraStream::Type::Direct)
> +			continue;
> +
> +		/*
> +		 * Other eligible buffers might be waiting to get post-processed.
> +		 * So wait for their turn before sendCaptureResults() for the
> +		 * descriptor.
> +		 */
> +		if (buffer.status == Camera3RequestDescriptor::Status::Pending)
> +			return;
> +
> +		if (!hasPostProcessingErrors &&
> +		    buffer.status == Camera3RequestDescriptor::Status::Error)
> +			hasPostProcessingErrors = true;
> +	}
> +
> +	if (hasPostProcessingErrors)
> +		request->status_ = Camera3RequestDescriptor::Status::Error;
> +	else
> +		request->status_ = Camera3RequestDescriptor::Status::Success;
> +
> +	locker.unlock();
> +
> +	sendCaptureResults();
> +}
> +
>  std::string CameraDevice::logPrefix() const
>  {
>  	return "'" + camera_->id() + "'";
> diff --git a/src/android/camera_device.h b/src/android/camera_device.h
> index 863cf414..1ef933da 100644
> --- a/src/android/camera_device.h
> +++ b/src/android/camera_device.h
> @@ -66,6 +66,9 @@ public:
>  	int configureStreams(camera3_stream_configuration_t *stream_list);
>  	int processCaptureRequest(camera3_capture_request_t *request);
>  	void requestComplete(libcamera::Request *request);
> +	void streamProcessingComplete(CameraStream *cameraStream,
> +				      Camera3RequestDescriptor *request,
> +				      Camera3RequestDescriptor::Status status);
>  
>  protected:
>  	std::string logPrefix() const override;
> @@ -94,6 +97,10 @@ private:
>  			 camera3_error_msg_code code) const;
>  	int processControls(Camera3RequestDescriptor *descriptor);
>  	void sendCaptureResults();
> +	void setBufferStatus(CameraStream *cameraStream,
> +			     Camera3RequestDescriptor::StreamBuffer &buffer,
> +			     Camera3RequestDescriptor *request,
> +			     Camera3RequestDescriptor::Status status);
>  	std::unique_ptr<CameraMetadata> getResultMetadata(
>  		const Camera3RequestDescriptor &descriptor) const;
>  
> diff --git a/src/android/camera_request.h b/src/android/camera_request.h
> index 05dabf89..3a2774e0 100644
> --- a/src/android/camera_request.h
> +++ b/src/android/camera_request.h
> @@ -8,6 +8,7 @@
>  #define __ANDROID_CAMERA_REQUEST_H__
>  
>  #include <memory>
> +#include <mutex>
>  #include <vector>
>  
>  #include <libcamera/base/class.h>
> @@ -37,6 +38,7 @@ public:
>  		std::unique_ptr<libcamera::FrameBuffer> frameBuffer;
>  		int fence;
>  		Status status;
> +		libcamera::FrameBuffer *internalBuffer = nullptr;
>  	};
>  
>  	Camera3RequestDescriptor(libcamera::Camera *camera,
> @@ -47,6 +49,8 @@ public:
>  
>  	uint32_t frameNumber_ = 0;
>  
> +	/* Protects buffers_ for post-processing streams. */
> +	std::mutex streamsProcessMutex_;
>  	std::vector<StreamBuffer> buffers_;
>  
>  	CameraMetadata settings_;
> diff --git a/src/android/camera_stream.cpp b/src/android/camera_stream.cpp
> index f44a2717..04cbef8c 100644
> --- a/src/android/camera_stream.cpp
> +++ b/src/android/camera_stream.cpp
> @@ -22,6 +22,7 @@
>  #include "camera_capabilities.h"
>  #include "camera_device.h"
>  #include "camera_metadata.h"
> +#include "post_processor.h"
>  
>  using namespace libcamera;
>  
> @@ -97,6 +98,18 @@ int CameraStream::configure()
>  		int ret = postProcessor_->configure(configuration(), output);
>  		if (ret)
>  			return ret;
> +
> +		postProcessor_->processComplete.connect(
> +			this, [&](Camera3RequestDescriptor *request, PostProcessor::Status status) {
> +				Camera3RequestDescriptor::Status bufferStatus =
> +					Camera3RequestDescriptor::Status::Error;
> +
> +				if (status == PostProcessor::Status::Success)
> +					bufferStatus = Camera3RequestDescriptor::Status::Success;

It looks weird to make Error a default (and thus special) case. Would
any of the following be better ?

				Camera3RequestDescriptor::Status bufferStatus;

				if (status == PostProcessor::Status::Success)
					bufferStatus = Camera3RequestDescriptor::Status::Success;
				else
					bufferStatus = Camera3RequestDescriptor::Status::Error;


				Camera3RequestDescriptor::Status bufferStatus =
					status == PostProcessor::Status::Success ?
					Camera3RequestDescriptor::Status::Success :
					Camera3RequestDescriptor::Status::Error;

I think I like the second option best.

> +
> +				cameraDevice_->streamProcessingComplete(this, request,
> +									bufferStatus);
> +			});
>  	}
>  
>  	if (type_ == Type::Internal) {
> diff --git a/src/android/jpeg/post_processor_jpeg.cpp b/src/android/jpeg/post_processor_jpeg.cpp
> index 699576ef..a001fede 100644
> --- a/src/android/jpeg/post_processor_jpeg.cpp
> +++ b/src/android/jpeg/post_processor_jpeg.cpp
> @@ -198,6 +198,7 @@ int PostProcessorJpeg::process(const FrameBuffer &source,
>  					 exif.data(), quality);
>  	if (jpeg_size < 0) {
>  		LOG(JPEG, Error) << "Failed to encode stream image";
> +		processComplete.emit(request, PostProcessor::Status::Error);

I think you can write Status::Error here and below, including in
post_processor_yuv.cpp (not above in camera_stream.cpp though).

>  		return jpeg_size;
>  	}
>  
> @@ -211,6 +212,7 @@ int PostProcessorJpeg::process(const FrameBuffer &source,
>  
>  	/* Update the JPEG result Metadata. */
>  	resultMetadata->addEntry(ANDROID_JPEG_SIZE, jpeg_size);
> +	processComplete.emit(request, PostProcessor::Status::Success);
>  
>  	return 0;
>  }
> diff --git a/src/android/post_processor.h b/src/android/post_processor.h
> index 27eaef88..14f5e8c7 100644
> --- a/src/android/post_processor.h
> +++ b/src/android/post_processor.h
> @@ -7,6 +7,8 @@
>  #ifndef __ANDROID_POST_PROCESSOR_H__
>  #define __ANDROID_POST_PROCESSOR_H__
>  
> +#include <libcamera/base/signal.h>
> +
>  #include <libcamera/framebuffer.h>
>  #include <libcamera/stream.h>
>  
> @@ -17,6 +19,11 @@ class Camera3RequestDescriptor;
>  class PostProcessor
>  {
>  public:
> +	enum class Status {
> +		Error,
> +		Success
> +	};
> +
>  	virtual ~PostProcessor() = default;
>  
>  	virtual int configure(const libcamera::StreamConfiguration &inCfg,
> @@ -24,6 +31,8 @@ public:
>  	virtual int process(const libcamera::FrameBuffer &source,
>  			    CameraBuffer *destination,
>  			    Camera3RequestDescriptor *request) = 0;
> +
> +	libcamera::Signal<Camera3RequestDescriptor *, Status> processComplete;
>  };
>  
>  #endif /* __ANDROID_POST_PROCESSOR_H__ */
> diff --git a/src/android/yuv/post_processor_yuv.cpp b/src/android/yuv/post_processor_yuv.cpp
> index 8110a1f1..fd364741 100644
> --- a/src/android/yuv/post_processor_yuv.cpp
> +++ b/src/android/yuv/post_processor_yuv.cpp
> @@ -51,14 +51,17 @@ int PostProcessorYuv::configure(const StreamConfiguration &inCfg,
>  
>  int PostProcessorYuv::process(const FrameBuffer &source,
>  			      CameraBuffer *destination,
> -			      [[maybe_unused]] Camera3RequestDescriptor *request)
> +			      Camera3RequestDescriptor *request)
>  {
> -	if (!isValidBuffers(source, *destination))
> +	if (!isValidBuffers(source, *destination)) {
> +		processComplete.emit(request, PostProcessor::Status::Error);
>  		return -EINVAL;
> +	}
>  
>  	const MappedFrameBuffer sourceMapped(&source, MappedFrameBuffer::MapFlag::Read);
>  	if (!sourceMapped.isValid()) {
>  		LOG(YUV, Error) << "Failed to mmap camera frame buffer";
> +		processComplete.emit(request, PostProcessor::Status::Error);
>  		return -EINVAL;
>  	}
>  
> @@ -76,9 +79,12 @@ int PostProcessorYuv::process(const FrameBuffer &source,
>  				    libyuv::FilterMode::kFilterBilinear);
>  	if (ret) {
>  		LOG(YUV, Error) << "Failed NV12 scaling: " << ret;
> +		processComplete.emit(request, PostProcessor::Status::Error);
>  		return -EINVAL;
>  	}
>  
> +	processComplete.emit(request, PostProcessor::Status::Success);
> +
>  	return 0;
>  }
>

Another comment.
On Thu, Oct 21, 2021 at 03:31:27AM +0300, Laurent Pinchart wrote:
> Hi Umang,
> 
> Thank you for the patch.
> 
> On Wed, Oct 20, 2021 at 04:12:09PM +0530, Umang Jain wrote:
> > Notify that the post processing for a request has been completed,
> > via a signal. A pointer to the descriptor which is tracking the
> > capture request is emitted along with the status of post processed
> > buffer. The function CameraDevice::streamProcessingComplete() will
> > finally set the status on the request descriptor and send capture
> > results back to the framework accordingly.
> > 
> > We also need to save a pointer to any internal buffers that might have
> > been allocated by CameraStream. The buffer should be returned back to
> > CameraStream just before capture results are sent.
> > 
> > A streamProcessMutex_ has been introduced here itself, which will be
> 
> Did you mean s/itself/as well/ ?
> 
> > applicable to guard access to descriptor->buffers_ when post-processing
> > is moved to be asynchronous in subsequent commits.
> > 
> > Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
> > ---
> >  src/android/camera_device.cpp            | 92 +++++++++++++++++++++---
> >  src/android/camera_device.h              |  7 ++
> >  src/android/camera_request.h             |  4 ++
> >  src/android/camera_stream.cpp            | 13 ++++
> >  src/android/jpeg/post_processor_jpeg.cpp |  2 +
> >  src/android/post_processor.h             |  9 +++
> >  src/android/yuv/post_processor_yuv.cpp   | 10 ++-
> >  7 files changed, 125 insertions(+), 12 deletions(-)
> > 
> > diff --git a/src/android/camera_device.cpp b/src/android/camera_device.cpp
> > index 806b4090..541c2c81 100644
> > --- a/src/android/camera_device.cpp
> > +++ b/src/android/camera_device.cpp
> > @@ -1117,6 +1117,15 @@ void CameraDevice::requestComplete(Request *request)
> >  	}
> >  
> >  	/* Handle post-processing. */
> > +	bool needsPostProcessing = false;
> > +	Camera3RequestDescriptor::Status processingStatus =
> > +		Camera3RequestDescriptor::Status::Pending;
> > +	/*
> > +	 * \todo Apply streamsProcessMutex_ when post-processing is adapted to run
> > +	 * asynchronously. If we introduce the streamsProcessMutex_ right away, the
> > +	 * lock will be held forever since it is synchronous at this point
> > +	 * (see streamProcessingComplete).
> > +	 */
> >  	for (auto &buffer : descriptor->buffers_) {
> >  		CameraStream *stream = buffer.stream;
> >  
> > @@ -1132,22 +1141,27 @@ void CameraDevice::requestComplete(Request *request)
> >  			continue;
> >  		}
> >  
> > -		int ret = stream->process(*src, buffer, descriptor);
> > -
> > -		/*
> > -		 * Return the FrameBuffer to the CameraStream now that we're
> > -		 * done processing it.
> > -		 */
> >  		if (stream->type() == CameraStream::Type::Internal)
> > -			stream->putBuffer(src);
> > +			buffer.internalBuffer = src;
> 
> Let's make the field name more self-explanatory. A possible candidate is
> sourceBuffer instead of internalBuffer.

I saw you've added an srcBuffer member in 3/4 to store the source buffer
for mapped streams as well. A single pointer should be enough, as you
check the stream type in setBufferStatus() before calling putBuffer().
However, we can't easily set this pointer in processCaptureRequest() for
mapped streams, and setting it in different locations depending on the
stream type isn't nice.

I'm tempted to have two pointers, internalBuffer and sourceBuffer, the
former set in processCaptureRequest() for internal streams only, and the
latter set here for both internal and mapped streams. You could then
remove the stream type check in setBufferStatus()() and replace it with
a 'if (buffer.internalBuffer)'.

> Could we do this in CameraDevice::processCaptureRequest(), just after
> calling cameraStream->getBuffer() ? I'll feel less worried about a leak
> if we store the buffer for later release right after acquiring it.
> 
> >  
> > +		needsPostProcessing = true;
> > +		int ret = stream->process(*src, buffer, descriptor);
> >  		if (ret) {
> > -			buffer.status = Camera3RequestDescriptor::Status::Error;
> > -			notifyError(descriptor->frameNumber_, stream->camera3Stream(),
> > -				    CAMERA3_MSG_ERROR_BUFFER);
> > +			setBufferStatus(stream, buffer, descriptor,
> > +					Camera3RequestDescriptor::Status::Error);
> > +			processingStatus = Camera3RequestDescriptor::Status::Error;
> >  		}
> 
> I think we need to improve error handling a little bit, in order to
> support multiple streams being post-processed. We need to complete the
> request in CameraDevice::streamProcessingComplete() when the last
> processing stream completes, so the number of post-processed streams
> need to be somehow recorded in the Camera3RequestDescriptor. It could be
> tempted to have a counter, but a
> 
> 	std::map<CameraStream *, StreamBuffer *> pendingPostProcess_;
> 
> could be better, as it will also remove the need for loops in
> streamProcessingComplete() to lookup the buffer from the stream and to
> check if the request has been fully processed. Accessing the map has to
> be done with the mutex held to avoid race conditions, but it's a bit
> more tricky than that. If we just add elements to the map here, we could
> race with streamProcessingComplete() as it could be called for the first
> post-processed stream before we have a chance to add the second one
> here. streamProcessingComplete() would then incorrectly think it has
> completed the last stream, and proceed to complete the request.
> 
> This race could be solved by holding the lock for the whole duration of
> the loop here, covering all calls to stream->process(), but it may be
> possible to do better. We could add entries to the map in
> processCaptureRequest() instead. We would need, here, to remove entries
> from the map if stream->process() fails, and complete the request if we
> remove the last entry (as otherwise, streamProcessingComplete() could
> complete all streams, then the last stream->process() call could fail,
> and nobody would complete the request).
> 
> Other designs may be possible.
> 
> >  	}
> >  
> > +	if (needsPostProcessing) {
> > +		if (processingStatus == Camera3RequestDescriptor::Status::Error) {
> > +			descriptor->status_ = processingStatus;
> > +			sendCaptureResults();
> > +		}
> > +
> > +		return;
> > +	}
> > +
> >  	descriptor->status_ = Camera3RequestDescriptor::Status::Success;
> >  	sendCaptureResults();
> >  }
> > @@ -1206,6 +1220,64 @@ void CameraDevice::sendCaptureResults()
> >  	}
> >  }
> >  
> > +void CameraDevice::setBufferStatus(CameraStream *cameraStream,
> > +				   Camera3RequestDescriptor::StreamBuffer &buffer,
> > +				   Camera3RequestDescriptor *request,
> > +				   Camera3RequestDescriptor::Status status)
> > +{
> > +	/*
> > +	 * Return the FrameBuffer to the CameraStream now that we're
> > +	 * done processing it.
> > +	 */
> > +	if (cameraStream->type() == CameraStream::Type::Internal)
> > +		cameraStream->putBuffer(buffer.internalBuffer);
> > +
> > +	buffer.status = status;
> > +	if (status != Camera3RequestDescriptor::Status::Success)
> > +		notifyError(request->frameNumber_, buffer.stream->camera3Stream(),
> > +			    CAMERA3_MSG_ERROR_BUFFER);
> > +}
> > +
> > +void CameraDevice::streamProcessingComplete(CameraStream *cameraStream,
> > +					    Camera3RequestDescriptor *request,
> > +					    Camera3RequestDescriptor::Status status)
> > +{
> > +	MutexLocker locker(request->streamsProcessMutex_);
> > +	for (auto &buffer : request->buffers_) {
> > +		if (buffer.stream != cameraStream)
> > +			continue;
> > +
> > +		setBufferStatus(cameraStream, buffer, request, status);
> > +	}
> > +
> > +	bool hasPostProcessingErrors = false;
> > +	for (auto &buffer : request->buffers_) {
> > +		if (cameraStream->type() == CameraStream::Type::Direct)
> > +			continue;
> > +
> > +		/*
> > +		 * Other eligible buffers might be waiting to get post-processed.
> > +		 * So wait for their turn before sendCaptureResults() for the
> > +		 * descriptor.
> > +		 */
> > +		if (buffer.status == Camera3RequestDescriptor::Status::Pending)
> > +			return;
> > +
> > +		if (!hasPostProcessingErrors &&
> > +		    buffer.status == Camera3RequestDescriptor::Status::Error)
> > +			hasPostProcessingErrors = true;
> > +	}
> > +
> > +	if (hasPostProcessingErrors)
> > +		request->status_ = Camera3RequestDescriptor::Status::Error;
> > +	else
> > +		request->status_ = Camera3RequestDescriptor::Status::Success;
> > +
> > +	locker.unlock();
> > +
> > +	sendCaptureResults();
> > +}
> > +
> >  std::string CameraDevice::logPrefix() const
> >  {
> >  	return "'" + camera_->id() + "'";
> > diff --git a/src/android/camera_device.h b/src/android/camera_device.h
> > index 863cf414..1ef933da 100644
> > --- a/src/android/camera_device.h
> > +++ b/src/android/camera_device.h
> > @@ -66,6 +66,9 @@ public:
> >  	int configureStreams(camera3_stream_configuration_t *stream_list);
> >  	int processCaptureRequest(camera3_capture_request_t *request);
> >  	void requestComplete(libcamera::Request *request);
> > +	void streamProcessingComplete(CameraStream *cameraStream,
> > +				      Camera3RequestDescriptor *request,
> > +				      Camera3RequestDescriptor::Status status);
> >  
> >  protected:
> >  	std::string logPrefix() const override;
> > @@ -94,6 +97,10 @@ private:
> >  			 camera3_error_msg_code code) const;
> >  	int processControls(Camera3RequestDescriptor *descriptor);
> >  	void sendCaptureResults();
> > +	void setBufferStatus(CameraStream *cameraStream,
> > +			     Camera3RequestDescriptor::StreamBuffer &buffer,
> > +			     Camera3RequestDescriptor *request,
> > +			     Camera3RequestDescriptor::Status status);
> >  	std::unique_ptr<CameraMetadata> getResultMetadata(
> >  		const Camera3RequestDescriptor &descriptor) const;
> >  
> > diff --git a/src/android/camera_request.h b/src/android/camera_request.h
> > index 05dabf89..3a2774e0 100644
> > --- a/src/android/camera_request.h
> > +++ b/src/android/camera_request.h
> > @@ -8,6 +8,7 @@
> >  #define __ANDROID_CAMERA_REQUEST_H__
> >  
> >  #include <memory>
> > +#include <mutex>
> >  #include <vector>
> >  
> >  #include <libcamera/base/class.h>
> > @@ -37,6 +38,7 @@ public:
> >  		std::unique_ptr<libcamera::FrameBuffer> frameBuffer;
> >  		int fence;
> >  		Status status;
> > +		libcamera::FrameBuffer *internalBuffer = nullptr;
> >  	};
> >  
> >  	Camera3RequestDescriptor(libcamera::Camera *camera,
> > @@ -47,6 +49,8 @@ public:
> >  
> >  	uint32_t frameNumber_ = 0;
> >  
> > +	/* Protects buffers_ for post-processing streams. */
> > +	std::mutex streamsProcessMutex_;
> >  	std::vector<StreamBuffer> buffers_;
> >  
> >  	CameraMetadata settings_;
> > diff --git a/src/android/camera_stream.cpp b/src/android/camera_stream.cpp
> > index f44a2717..04cbef8c 100644
> > --- a/src/android/camera_stream.cpp
> > +++ b/src/android/camera_stream.cpp
> > @@ -22,6 +22,7 @@
> >  #include "camera_capabilities.h"
> >  #include "camera_device.h"
> >  #include "camera_metadata.h"
> > +#include "post_processor.h"
> >  
> >  using namespace libcamera;
> >  
> > @@ -97,6 +98,18 @@ int CameraStream::configure()
> >  		int ret = postProcessor_->configure(configuration(), output);
> >  		if (ret)
> >  			return ret;
> > +
> > +		postProcessor_->processComplete.connect(
> > +			this, [&](Camera3RequestDescriptor *request, PostProcessor::Status status) {
> > +				Camera3RequestDescriptor::Status bufferStatus =
> > +					Camera3RequestDescriptor::Status::Error;
> > +
> > +				if (status == PostProcessor::Status::Success)
> > +					bufferStatus = Camera3RequestDescriptor::Status::Success;
> 
> It looks weird to make Error a default (and thus special) case. Would
> any of the following be better ?
> 
> 				Camera3RequestDescriptor::Status bufferStatus;
> 
> 				if (status == PostProcessor::Status::Success)
> 					bufferStatus = Camera3RequestDescriptor::Status::Success;
> 				else
> 					bufferStatus = Camera3RequestDescriptor::Status::Error;
> 
> 
> 				Camera3RequestDescriptor::Status bufferStatus =
> 					status == PostProcessor::Status::Success ?
> 					Camera3RequestDescriptor::Status::Success :
> 					Camera3RequestDescriptor::Status::Error;
> 
> I think I like the second option best.
> 
> > +
> > +				cameraDevice_->streamProcessingComplete(this, request,
> > +									bufferStatus);
> > +			});
> >  	}
> >  
> >  	if (type_ == Type::Internal) {
> > diff --git a/src/android/jpeg/post_processor_jpeg.cpp b/src/android/jpeg/post_processor_jpeg.cpp
> > index 699576ef..a001fede 100644
> > --- a/src/android/jpeg/post_processor_jpeg.cpp
> > +++ b/src/android/jpeg/post_processor_jpeg.cpp
> > @@ -198,6 +198,7 @@ int PostProcessorJpeg::process(const FrameBuffer &source,
> >  					 exif.data(), quality);
> >  	if (jpeg_size < 0) {
> >  		LOG(JPEG, Error) << "Failed to encode stream image";
> > +		processComplete.emit(request, PostProcessor::Status::Error);
> 
> I think you can write Status::Error here and below, including in
> post_processor_yuv.cpp (not above in camera_stream.cpp though).
> 
> >  		return jpeg_size;
> >  	}
> >  
> > @@ -211,6 +212,7 @@ int PostProcessorJpeg::process(const FrameBuffer &source,
> >  
> >  	/* Update the JPEG result Metadata. */
> >  	resultMetadata->addEntry(ANDROID_JPEG_SIZE, jpeg_size);
> > +	processComplete.emit(request, PostProcessor::Status::Success);
> >  
> >  	return 0;
> >  }
> > diff --git a/src/android/post_processor.h b/src/android/post_processor.h
> > index 27eaef88..14f5e8c7 100644
> > --- a/src/android/post_processor.h
> > +++ b/src/android/post_processor.h
> > @@ -7,6 +7,8 @@
> >  #ifndef __ANDROID_POST_PROCESSOR_H__
> >  #define __ANDROID_POST_PROCESSOR_H__
> >  
> > +#include <libcamera/base/signal.h>
> > +
> >  #include <libcamera/framebuffer.h>
> >  #include <libcamera/stream.h>
> >  
> > @@ -17,6 +19,11 @@ class Camera3RequestDescriptor;
> >  class PostProcessor
> >  {
> >  public:
> > +	enum class Status {
> > +		Error,
> > +		Success
> > +	};
> > +
> >  	virtual ~PostProcessor() = default;
> >  
> >  	virtual int configure(const libcamera::StreamConfiguration &inCfg,
> > @@ -24,6 +31,8 @@ public:
> >  	virtual int process(const libcamera::FrameBuffer &source,
> >  			    CameraBuffer *destination,
> >  			    Camera3RequestDescriptor *request) = 0;
> > +
> > +	libcamera::Signal<Camera3RequestDescriptor *, Status> processComplete;
> >  };
> >  
> >  #endif /* __ANDROID_POST_PROCESSOR_H__ */
> > diff --git a/src/android/yuv/post_processor_yuv.cpp b/src/android/yuv/post_processor_yuv.cpp
> > index 8110a1f1..fd364741 100644
> > --- a/src/android/yuv/post_processor_yuv.cpp
> > +++ b/src/android/yuv/post_processor_yuv.cpp
> > @@ -51,14 +51,17 @@ int PostProcessorYuv::configure(const StreamConfiguration &inCfg,
> >  
> >  int PostProcessorYuv::process(const FrameBuffer &source,
> >  			      CameraBuffer *destination,
> > -			      [[maybe_unused]] Camera3RequestDescriptor *request)
> > +			      Camera3RequestDescriptor *request)
> >  {
> > -	if (!isValidBuffers(source, *destination))
> > +	if (!isValidBuffers(source, *destination)) {
> > +		processComplete.emit(request, PostProcessor::Status::Error);
> >  		return -EINVAL;
> > +	}
> >  
> >  	const MappedFrameBuffer sourceMapped(&source, MappedFrameBuffer::MapFlag::Read);
> >  	if (!sourceMapped.isValid()) {
> >  		LOG(YUV, Error) << "Failed to mmap camera frame buffer";
> > +		processComplete.emit(request, PostProcessor::Status::Error);
> >  		return -EINVAL;
> >  	}
> >  
> > @@ -76,9 +79,12 @@ int PostProcessorYuv::process(const FrameBuffer &source,
> >  				    libyuv::FilterMode::kFilterBilinear);
> >  	if (ret) {
> >  		LOG(YUV, Error) << "Failed NV12 scaling: " << ret;
> > +		processComplete.emit(request, PostProcessor::Status::Error);
> >  		return -EINVAL;
> >  	}
> >  
> > +	processComplete.emit(request, PostProcessor::Status::Success);
> > +
> >  	return 0;
> >  }
> >

Hi Laurent,

On 10/21/21 6:01 AM, Laurent Pinchart wrote:
> Hi Umang,
>
> Thank you for the patch.
>
> On Wed, Oct 20, 2021 at 04:12:09PM +0530, Umang Jain wrote:
>> Notify that the post processing for a request has been completed,
>> via a signal. A pointer to the descriptor which is tracking the
>> capture request is emitted along with the status of post processed
>> buffer. The function CameraDevice::streamProcessingComplete() will
>> finally set the status on the request descriptor and send capture
>> results back to the framework accordingly.
>>
>> We also need to save a pointer to any internal buffers that might have
>> been allocated by CameraStream. The buffer should be returned back to
>> CameraStream just before capture results are sent.
>>
>> A streamProcessMutex_ has been introduced here itself, which will be
> Did you mean s/itself/as well/ ?
>
>> applicable to guard access to descriptor->buffers_ when post-processing
>> is moved to be asynchronous in subsequent commits.
>>
>> Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
>> ---
>>   src/android/camera_device.cpp            | 92 +++++++++++++++++++++---
>>   src/android/camera_device.h              |  7 ++
>>   src/android/camera_request.h             |  4 ++
>>   src/android/camera_stream.cpp            | 13 ++++
>>   src/android/jpeg/post_processor_jpeg.cpp |  2 +
>>   src/android/post_processor.h             |  9 +++
>>   src/android/yuv/post_processor_yuv.cpp   | 10 ++-
>>   7 files changed, 125 insertions(+), 12 deletions(-)
>>
>> diff --git a/src/android/camera_device.cpp b/src/android/camera_device.cpp
>> index 806b4090..541c2c81 100644
>> --- a/src/android/camera_device.cpp
>> +++ b/src/android/camera_device.cpp
>> @@ -1117,6 +1117,15 @@ void CameraDevice::requestComplete(Request *request)
>>   	}
>>   
>>   	/* Handle post-processing. */
>> +	bool needsPostProcessing = false;
>> +	Camera3RequestDescriptor::Status processingStatus =
>> +		Camera3RequestDescriptor::Status::Pending;
>> +	/*
>> +	 * \todo Apply streamsProcessMutex_ when post-processing is adapted to run
>> +	 * asynchronously. If we introduce the streamsProcessMutex_ right away, the
>> +	 * lock will be held forever since it is synchronous at this point
>> +	 * (see streamProcessingComplete).
>> +	 */
>>   	for (auto &buffer : descriptor->buffers_) {
>>   		CameraStream *stream = buffer.stream;
>>   
>> @@ -1132,22 +1141,27 @@ void CameraDevice::requestComplete(Request *request)
>>   			continue;
>>   		}
>>   
>> -		int ret = stream->process(*src, buffer, descriptor);
>> -
>> -		/*
>> -		 * Return the FrameBuffer to the CameraStream now that we're
>> -		 * done processing it.
>> -		 */
>>   		if (stream->type() == CameraStream::Type::Internal)
>> -			stream->putBuffer(src);
>> +			buffer.internalBuffer = src;
> Let's make the field name more self-explanatory. A possible candidate is
> sourceBuffer instead of internalBuffer.
>
> Could we do this in CameraDevice::processCaptureRequest(), just after
> calling cameraStream->getBuffer() ? I'll feel less worried about a leak
> if we store the buffer for later release right after acquiring it.


Ack.

>
>>   
>> +		needsPostProcessing = true;
>> +		int ret = stream->process(*src, buffer, descriptor);
>>   		if (ret) {
>> -			buffer.status = Camera3RequestDescriptor::Status::Error;
>> -			notifyError(descriptor->frameNumber_, stream->camera3Stream(),
>> -				    CAMERA3_MSG_ERROR_BUFFER);
>> +			setBufferStatus(stream, buffer, descriptor,
>> +					Camera3RequestDescriptor::Status::Error);
>> +			processingStatus = Camera3RequestDescriptor::Status::Error;
>>   		}
> I think we need to improve error handling a little bit, in order to
> support multiple streams being post-processed. We need to complete the
> request in CameraDevice::streamProcessingComplete() when the last
> processing stream completes, so the number of post-processed streams
> need to be somehow recorded in the Camera3RequestDescriptor. It could be
> tempted to have a counter, but a


I have implemented a counter based solution, it still didn't address all 
the corner cases. Since we have two  path of error handling (synchronous 
error and asynchronous error), a counter based implementation was 
probably too verbose with much of code duplication to handle various 
scenarios.


>
> 	std::map<CameraStream *, StreamBuffer *> pendingPostProcess_;
>
> could be better, as it will also remove the need for loops in
> streamProcessingComplete() to lookup the buffer from the stream and to
> check if the request has been fully processed. Accessing the map has to
> be done with the mutex held to avoid race conditions, but it's a bit
> more tricky than that. If we just add elements to the map here, we could


Good, so you do understand so many looping lookups in 
streamProcessingComplete.

I broadly feel okay with std::map<CameraStream *, StreamBuffer *> 
pendingPostProcess_; as long as it resides inside the descriptor. For 
me, it avoids lookups, and can address the \todo in 3/4.

Having said that, I feel a bit wary of introducing more data structures 
for management. We already have a queue of post-processing (convert to 
std:deque if we want to access the queued requests for post-processing) 
and now we will have another map to tracking the requests. I wonder if 
we can get away with a PostProcessorWorker's std::deque, with the 
benefits of the map. But again, we have to take care of exposure / mutex 
with main thread, which can lead to subtle bugs and unwanted waiting on 
each thread

Now I think about it, the pendingPostProcess_ map is about Stream's 
pending processing _per descriptor_, whereas the PostProcessorWorker's 
queue is replacement for Thread's message queue. Hmm.

> race with streamProcessingComplete() as it could be called for the first
> post-processed stream before we have a chance to add the second one
> here. streamProcessingComplete() would then incorrectly think it has
> completed the last stream, and proceed to complete the request.
>
> This race could be solved by holding the lock for the whole duration of
> the loop here, covering all calls to stream->process(), but it may be


Yes,  I am considering this in current implementation too. The way it 
will look like, is first queue up all the post-processing requests to 
PostProcessorWoe, only then, allow any of the 
slot(streamProcessingComplete) to get executed. A simple mutex hold can 
do that

> possible to do better. We could add entries to the map in
> processCaptureRequest() instead. We would need, here, to remove entries


I am not so sure about this, We could add entries in 
processCaptureRequest() but it feels too early. Let me try to address 
other comments, and I can iterate on this on top.

> from the map if stream->process() fails, and complete the request if we
> remove the last entry (as otherwise, streamProcessingComplete() could
> complete all streams, then the last stream->process() call could fail,
> and nobody would complete the request).


This is still a bit tricky to handle. What's the de-facto criteria to 
remove entries from the map (not just the error path) ?

Assuming we hold the lock for entire duration of

     Locker.lock();

     for {
         ...
         int ret = stream->process(...);
         if (ret) {
             descriptor.pendingPostProcess_.erase(stream);
             setBufferStatus(stream, error);

             if (descriptor.pendingPostProcess_.size() == 0)
                 completeDescriptor (error);

         }

     }
     locker.unlock();

....

streamProcessingComplete(..., bufferStatus)

{

     Locker.lock();

descriptor.pendingPostProcess_.erase(stream);
     setBufferStatus(stream, bufferStatus);

     if (descriptor.pendingPostProcess_.size() == 0)
         completeDescriptor (?);

}

the ? indicates with what status I should complete the descriptor? I 
would probably need to iterate over all the descriptor's buffer status 
to see if any of the (previous)buffer has failed to set error status on 
the descriptor overall? I think so, we would still need a look up loop 
here, I can't see deciphering this from the map.


Are we getting too complicated with this? I have started to feel so ...

>
> Other designs may be possible.
>
>>   	}
>>   
>> +	if (needsPostProcessing) {
>> +		if (processingStatus == Camera3RequestDescriptor::Status::Error) {
>> +			descriptor->status_ = processingStatus;
>> +			sendCaptureResults();
>> +		}
>> +
>> +		return;
>> +	}
>> +
>>   	descriptor->status_ = Camera3RequestDescriptor::Status::Success;
>>   	sendCaptureResults();
>>   }
>> @@ -1206,6 +1220,64 @@ void CameraDevice::sendCaptureResults()
>>   	}
>>   }
>>   
>> +void CameraDevice::setBufferStatus(CameraStream *cameraStream,
>> +				   Camera3RequestDescriptor::StreamBuffer &buffer,
>> +				   Camera3RequestDescriptor *request,
>> +				   Camera3RequestDescriptor::Status status)
>> +{
>> +	/*
>> +	 * Return the FrameBuffer to the CameraStream now that we're
>> +	 * done processing it.
>> +	 */
>> +	if (cameraStream->type() == CameraStream::Type::Internal)
>> +		cameraStream->putBuffer(buffer.internalBuffer);
>> +
>> +	buffer.status = status;
>> +	if (status != Camera3RequestDescriptor::Status::Success)
>> +		notifyError(request->frameNumber_, buffer.stream->camera3Stream(),
>>   +			    CAMERA3_MSG_ERROR_BUFFER);
>> +}
>> +
>> +void CameraDevice::streamProcessingComplete(CameraStream *cameraStream,
>> +					    Camera3RequestDescriptor *request,
>> +					    Camera3RequestDescriptor::Status status)
>> +{
>> +	MutexLocker locker(request->streamsProcessMutex_);
>> +	for (auto &buffer : request->buffers_) {
>> +		if (buffer.stream != cameraStream)
>> +			continue;
>> +
>> +		setBufferStatus(cameraStream, buffer, request, status);
>> +	}
>> +
>> +	bool hasPostProcessingErrors = false;
>> +	for (auto &buffer : request->buffers_) {
>> +		if (cameraStream->type() == CameraStream::Type::Direct)
>> +			continue;
>> +
>> +		/*
>> +		 * Other eligible buffers might be waiting to get post-processed.
>> +		 * So wait for their turn before sendCaptureResults() for the
>> +		 * descriptor.
>> +		 */
>> +		if (buffer.status == Camera3RequestDescriptor::Status::Pending)
>> +			return;
>> +
>> +		if (!hasPostProcessingErrors &&
>> +		    buffer.status == Camera3RequestDescriptor::Status::Error)
>> +			hasPostProcessingErrors = true;
>> +	}
>> +
>> +	if (hasPostProcessingErrors)
>> +		request->status_ = Camera3RequestDescriptor::Status::Error;
>> +	else
>> +		request->status_ = Camera3RequestDescriptor::Status::Success;
>> +
>> +	locker.unlock();
>> +
>> +	sendCaptureResults();
>> +}
>> +
>>   std::string CameraDevice::logPrefix() const
>>   {
>>   	return "'" + camera_->id() + "'";
>> diff --git a/src/android/camera_device.h b/src/android/camera_device.h
>> index 863cf414..1ef933da 100644
>> --- a/src/android/camera_device.h
>> +++ b/src/android/camera_device.h
>> @@ -66,6 +66,9 @@ public:
>>   	int configureStreams(camera3_stream_configuration_t *stream_list);
>>   	int processCaptureRequest(camera3_capture_request_t *request);
>>   	void requestComplete(libcamera::Request *request);
>> +	void streamProcessingComplete(CameraStream *cameraStream,
>> +				      Camera3RequestDescriptor *request,
>> +				      Camera3RequestDescriptor::Status status);
>>   
>>   protected:
>>   	std::string logPrefix() const override;
>> @@ -94,6 +97,10 @@ private:
>>   			 camera3_error_msg_code code) const;
>>   	int processControls(Camera3RequestDescriptor *descriptor);
>>   	void sendCaptureResults();
>> +	void setBufferStatus(CameraStream *cameraStream,
>> +			     Camera3RequestDescriptor::StreamBuffer &buffer,
>> +			     Camera3RequestDescriptor *request,
>> +			     Camera3RequestDescriptor::Status status);
>>   	std::unique_ptr<CameraMetadata> getResultMetadata(
>>   		const Camera3RequestDescriptor &descriptor) const;
>>   
>> diff --git a/src/android/camera_request.h b/src/android/camera_request.h
>> index 05dabf89..3a2774e0 100644
>> --- a/src/android/camera_request.h
>> +++ b/src/android/camera_request.h
>> @@ -8,6 +8,7 @@
>>   #define __ANDROID_CAMERA_REQUEST_H__
>>   
>>   #include <memory>
>> +#include <mutex>
>>   #include <vector>
>>   
>>   #include <libcamera/base/class.h>
>> @@ -37,6 +38,7 @@ public:
>>   		std::unique_ptr<libcamera::FrameBuffer> frameBuffer;
>>   		int fence;
>>   		Status status;
>> +		libcamera::FrameBuffer *internalBuffer = nullptr;
>>   	};
>>   
>>   	Camera3RequestDescriptor(libcamera::Camera *camera,
>> @@ -47,6 +49,8 @@ public:
>>   
>>   	uint32_t frameNumber_ = 0;
>>   
>> +	/* Protects buffers_ for post-processing streams. */
>> +	std::mutex streamsProcessMutex_;
>>   	std::vector<StreamBuffer> buffers_;
>>   
>>   	CameraMetadata settings_;
>> diff --git a/src/android/camera_stream.cpp b/src/android/camera_stream.cpp
>> index f44a2717..04cbef8c 100644
>> --- a/src/android/camera_stream.cpp
>> +++ b/src/android/camera_stream.cpp
>> @@ -22,6 +22,7 @@
>>   #include "camera_capabilities.h"
>>   #include "camera_device.h"
>>   #include "camera_metadata.h"
>> +#include "post_processor.h"
>>   
>>   using namespace libcamera;
>>   
>> @@ -97,6 +98,18 @@ int CameraStream::configure()
>>   		int ret = postProcessor_->configure(configuration(), output);
>>   		if (ret)
>>   			return ret;
>> +
>> +		postProcessor_->processComplete.connect(
>> +			this, [&](Camera3RequestDescriptor *request, PostProcessor::Status status) {
>> +				Camera3RequestDescriptor::Status bufferStatus =
>> +					Camera3RequestDescriptor::Status::Error;
>> +
>> +				if (status == PostProcessor::Status::Success)
>> +					bufferStatus = Camera3RequestDescriptor::Status::Success;
> It looks weird to make Error a default (and thus special) case. Would
> any of the following be better ?
>
> 				Camera3RequestDescriptor::Status bufferStatus;
>
> 				if (status == PostProcessor::Status::Success)
> 					bufferStatus = Camera3RequestDescriptor::Status::Success;
> 				else
> 					bufferStatus = Camera3RequestDescriptor::Status::Error;
>
>
> 				Camera3RequestDescriptor::Status bufferStatus =
> 					status == PostProcessor::Status::Success ?
> 					Camera3RequestDescriptor::Status::Success :
> 					Camera3RequestDescriptor::Status::Error;
>
> I think I like the second option best.
>
>> +
>> +				cameraDevice_->streamProcessingComplete(this, request,
>> +									bufferStatus);
>> +			});
>>   	}
>>   
>>   	if (type_ == Type::Internal) {
>> diff --git a/src/android/jpeg/post_processor_jpeg.cpp b/src/android/jpeg/post_processor_jpeg.cpp
>> index 699576ef..a001fede 100644
>> --- a/src/android/jpeg/post_processor_jpeg.cpp
>> +++ b/src/android/jpeg/post_processor_jpeg.cpp
>> @@ -198,6 +198,7 @@ int PostProcessorJpeg::process(const FrameBuffer &source,
>>   					 exif.data(), quality);
>>   	if (jpeg_size < 0) {
>>   		LOG(JPEG, Error) << "Failed to encode stream image";
>> +		processComplete.emit(request, PostProcessor::Status::Error);
> I think you can write Status::Error here and below, including in
> post_processor_yuv.cpp (not above in camera_stream.cpp though).
>
>>   		return jpeg_size;
>>   	}
>>   
>> @@ -211,6 +212,7 @@ int PostProcessorJpeg::process(const FrameBuffer &source,
>>   
>>   	/* Update the JPEG result Metadata. */
>>   	resultMetadata->addEntry(ANDROID_JPEG_SIZE, jpeg_size);
>> +	processComplete.emit(request, PostProcessor::Status::Success);
>>   
>>   	return 0;
>>   }
>> diff --git a/src/android/post_processor.h b/src/android/post_processor.h
>> index 27eaef88..14f5e8c7 100644
>> --- a/src/android/post_processor.h
>> +++ b/src/android/post_processor.h
>> @@ -7,6 +7,8 @@
>>   #ifndef __ANDROID_POST_PROCESSOR_H__
>>   #define __ANDROID_POST_PROCESSOR_H__
>>   
>> +#include <libcamera/base/signal.h>
>> +
>>   #include <libcamera/framebuffer.h>
>>   #include <libcamera/stream.h>
>>   
>> @@ -17,6 +19,11 @@ class Camera3RequestDescriptor;
>>   class PostProcessor
>>   {
>>   public:
>> +	enum class Status {
>> +		Error,
>> +		Success
>> +	};
>> +
>>   	virtual ~PostProcessor() = default;
>>   
>>   	virtual int configure(const libcamera::StreamConfiguration &inCfg,
>> @@ -24,6 +31,8 @@ public:
>>   	virtual int process(const libcamera::FrameBuffer &source,
>>   			    CameraBuffer *destination,
>>   			    Camera3RequestDescriptor *request) = 0;
>> +
>> +	libcamera::Signal<Camera3RequestDescriptor *, Status> processComplete;
>>   };
>>   
>>   #endif /* __ANDROID_POST_PROCESSOR_H__ */
>> diff --git a/src/android/yuv/post_processor_yuv.cpp b/src/android/yuv/post_processor_yuv.cpp
>> index 8110a1f1..fd364741 100644
>> --- a/src/android/yuv/post_processor_yuv.cpp
>> +++ b/src/android/yuv/post_processor_yuv.cpp
>> @@ -51,14 +51,17 @@ int PostProcessorYuv::configure(const StreamConfiguration &inCfg,
>>   
>>   int PostProcessorYuv::process(const FrameBuffer &source,
>>   			      CameraBuffer *destination,
>> -			      [[maybe_unused]] Camera3RequestDescriptor *request)
>> +			      Camera3RequestDescriptor *request)
>>   {
>> -	if (!isValidBuffers(source, *destination))
>> +	if (!isValidBuffers(source, *destination)) {
>> +		processComplete.emit(request, PostProcessor::Status::Error);
>>   		return -EINVAL;
>> +	}
>>   
>>   	const MappedFrameBuffer sourceMapped(&source, MappedFrameBuffer::MapFlag::Read);
>>   	if (!sourceMapped.isValid()) {
>>   		LOG(YUV, Error) << "Failed to mmap camera frame buffer";
>> +		processComplete.emit(request, PostProcessor::Status::Error);
>>   		return -EINVAL;
>>   	}
>>   
>> @@ -76,9 +79,12 @@ int PostProcessorYuv::process(const FrameBuffer &source,
>>   				    libyuv::FilterMode::kFilterBilinear);
>>   	if (ret) {
>>   		LOG(YUV, Error) << "Failed NV12 scaling: " << ret;
>> +		processComplete.emit(request, PostProcessor::Status::Error);
>>   		return -EINVAL;
>>   	}
>>   
>> +	processComplete.emit(request, PostProcessor::Status::Success);
>> +
>>   	return 0;
>>   }
>>

Hi Umang,

On Thu, Oct 21, 2021 at 11:05:44AM +0530, Umang Jain wrote:
> On 10/21/21 6:01 AM, Laurent Pinchart wrote:
> > On Wed, Oct 20, 2021 at 04:12:09PM +0530, Umang Jain wrote:
> >> Notify that the post processing for a request has been completed,
> >> via a signal. A pointer to the descriptor which is tracking the
> >> capture request is emitted along with the status of post processed
> >> buffer. The function CameraDevice::streamProcessingComplete() will
> >> finally set the status on the request descriptor and send capture
> >> results back to the framework accordingly.
> >>
> >> We also need to save a pointer to any internal buffers that might have
> >> been allocated by CameraStream. The buffer should be returned back to
> >> CameraStream just before capture results are sent.
> >>
> >> A streamProcessMutex_ has been introduced here itself, which will be
> > Did you mean s/itself/as well/ ?
> >
> >> applicable to guard access to descriptor->buffers_ when post-processing
> >> is moved to be asynchronous in subsequent commits.
> >>
> >> Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
> >> ---
> >>   src/android/camera_device.cpp            | 92 +++++++++++++++++++++---
> >>   src/android/camera_device.h              |  7 ++
> >>   src/android/camera_request.h             |  4 ++
> >>   src/android/camera_stream.cpp            | 13 ++++
> >>   src/android/jpeg/post_processor_jpeg.cpp |  2 +
> >>   src/android/post_processor.h             |  9 +++
> >>   src/android/yuv/post_processor_yuv.cpp   | 10 ++-
> >>   7 files changed, 125 insertions(+), 12 deletions(-)
> >>
> >> diff --git a/src/android/camera_device.cpp b/src/android/camera_device.cpp
> >> index 806b4090..541c2c81 100644
> >> --- a/src/android/camera_device.cpp
> >> +++ b/src/android/camera_device.cpp
> >> @@ -1117,6 +1117,15 @@ void CameraDevice::requestComplete(Request *request)
> >>   	}
> >>   
> >>   	/* Handle post-processing. */
> >> +	bool needsPostProcessing = false;
> >> +	Camera3RequestDescriptor::Status processingStatus =
> >> +		Camera3RequestDescriptor::Status::Pending;
> >> +	/*
> >> +	 * \todo Apply streamsProcessMutex_ when post-processing is adapted to run
> >> +	 * asynchronously. If we introduce the streamsProcessMutex_ right away, the
> >> +	 * lock will be held forever since it is synchronous at this point
> >> +	 * (see streamProcessingComplete).
> >> +	 */
> >>   	for (auto &buffer : descriptor->buffers_) {
> >>   		CameraStream *stream = buffer.stream;
> >>   
> >> @@ -1132,22 +1141,27 @@ void CameraDevice::requestComplete(Request *request)
> >>   			continue;
> >>   		}
> >>   
> >> -		int ret = stream->process(*src, buffer, descriptor);
> >> -
> >> -		/*
> >> -		 * Return the FrameBuffer to the CameraStream now that we're
> >> -		 * done processing it.
> >> -		 */
> >>   		if (stream->type() == CameraStream::Type::Internal)
> >> -			stream->putBuffer(src);
> >> +			buffer.internalBuffer = src;
> >
> > Let's make the field name more self-explanatory. A possible candidate is
> > sourceBuffer instead of internalBuffer.
> >
> > Could we do this in CameraDevice::processCaptureRequest(), just after
> > calling cameraStream->getBuffer() ? I'll feel less worried about a leak
> > if we store the buffer for later release right after acquiring it.
> 
> Ack.
> 
> >>   
> >> +		needsPostProcessing = true;
> >> +		int ret = stream->process(*src, buffer, descriptor);
> >>   		if (ret) {
> >> -			buffer.status = Camera3RequestDescriptor::Status::Error;
> >> -			notifyError(descriptor->frameNumber_, stream->camera3Stream(),
> >> -				    CAMERA3_MSG_ERROR_BUFFER);
> >> +			setBufferStatus(stream, buffer, descriptor,
> >> +					Camera3RequestDescriptor::Status::Error);
> >> +			processingStatus = Camera3RequestDescriptor::Status::Error;
> >>   		}
> >
> > I think we need to improve error handling a little bit, in order to
> > support multiple streams being post-processed. We need to complete the
> > request in CameraDevice::streamProcessingComplete() when the last
> > processing stream completes, so the number of post-processed streams
> > need to be somehow recorded in the Camera3RequestDescriptor. It could be
> > tempted to have a counter, but a
> 
> I have implemented a counter based solution, it still didn't address all 
> the corner cases. Since we have two  path of error handling (synchronous 
> error and asynchronous error), a counter based implementation was 
> probably too verbose with much of code duplication to handle various 
> scenarios.
> 
> >
> > 	std::map<CameraStream *, StreamBuffer *> pendingPostProcess_;
> >
> > could be better, as it will also remove the need for loops in
> > streamProcessingComplete() to lookup the buffer from the stream and to
> > check if the request has been fully processed. Accessing the map has to
> > be done with the mutex held to avoid race conditions, but it's a bit
> > more tricky than that. If we just add elements to the map here, we could
> 
> Good, so you do understand so many looping lookups in 
> streamProcessingComplete.
> 
> I broadly feel okay with std::map<CameraStream *, StreamBuffer *> 
> pendingPostProcess_; as long as it resides inside the descriptor. For 
> me, it avoids lookups, and can address the \todo in 3/4.
> 
> Having said that, I feel a bit wary of introducing more data structures 
> for management. We already have a queue of post-processing (convert to 
> std:deque if we want to access the queued requests for post-processing) 
> and now we will have another map to tracking the requests. I wonder if 
> we can get away with a PostProcessorWorker's std::deque, with the 
> benefits of the map. But again, we have to take care of exposure / mutex 
> with main thread, which can lead to subtle bugs and unwanted waiting on 
> each thread
> 
> Now I think about it, the pendingPostProcess_ map is about Stream's 
> pending processing _per descriptor_, whereas the PostProcessorWorker's 
> queue is replacement for Thread's message queue. Hmm.

That's right, those two data structures are independent from each other.

> > race with streamProcessingComplete() as it could be called for the first
> > post-processed stream before we have a chance to add the second one
> > here. streamProcessingComplete() would then incorrectly think it has
> > completed the last stream, and proceed to complete the request.
> >
> > This race could be solved by holding the lock for the whole duration of
> > the loop here, covering all calls to stream->process(), but it may be
> 
> Yes,  I am considering this in current implementation too. The way it 
> will look like, is first queue up all the post-processing requests to 
> PostProcessorWoe, only then, allow any of the 
> slot(streamProcessingComplete) to get executed. A simple mutex hold can 
> do that

I usually try to minimize the amount of code covered by locks, and focus
on data access only if possible instead of keeping the lock held over
the callbacks. Let's see if that's possible. There's a tricky part
though, as sendCaptureResults() is called from two different threads
(synchronously with request queuing in error paths and asynchronously in
the completion path), we currently have a race condition.

Thread A							Thread B
-----------------------------------------------------------------------------------------------------------

MutexLocker lock(descriptorsMutex_);
while (!descriptors_.empty() &&
       !descriptors_.front()->isPending()) {
        auto descriptor = std::move(descriptors_.front());
        descriptors_.pop();

        lock.unlock();
								MutexLocker lock(descriptorsMutex_);
								while (!descriptors_.empty() &&
								       !descriptors_.front()->isPending()) {
									auto descriptor = std::move(descriptors_.front());
									descriptors_.pop();

									lock.unlock();

									...

									callbacks_->process_capture_result(callbacks_,
													   &captureResult);

									lock.lock();
								}
	...

        callbacks_->process_capture_result(callbacks_,
					   &captureResult);

        lock.lock();
}

Thread A gets the request at the top of the queue, thread B gets the
next one, and signals its completion before thread A.

It's likely possible to implement something clever here, to minimize the
locked sections and still be correct, but that may be unnecessary
optimization. We could start by holding the lock for the whole duration
of the function. In that case, I would remove the lock from
sendCaptureResults() completely, and call the function with the lock
held in completeDescriptor().

> > possible to do better. We could add entries to the map in
> > processCaptureRequest() instead. We would need, here, to remove entries
> 
> I am not so sure about this, We could add entries in 
> processCaptureRequest() but it feels too early. Let me try to address 
> other comments, and I can iterate on this on top.
> 
> > from the map if stream->process() fails, and complete the request if we
> > remove the last entry (as otherwise, streamProcessingComplete() could
> > complete all streams, then the last stream->process() call could fail,
> > and nobody would complete the request).
> 
> This is still a bit tricky to handle. What's the de-facto criteria to 
> remove entries from the map (not just the error path) ?
> 
> Assuming we hold the lock for entire duration of
> 
>      Locker.lock();
> 
>      for {
>          ...
>          int ret = stream->process(...);
>          if (ret) {
>              descriptor.pendingPostProcess_.erase(stream);
>              setBufferStatus(stream, error);
> 
>              if (descriptor.pendingPostProcess_.size() == 0)
>                  completeDescriptor (error);
> 
>          }
> 
>      }
>      locker.unlock();
> 
> ....
> 
> streamProcessingComplete(..., bufferStatus)
> 
> {
> 
>      Locker.lock();
> 
> descriptor.pendingPostProcess_.erase(stream);
>      setBufferStatus(stream, bufferStatus);
> 
>      if (descriptor.pendingPostProcess_.size() == 0)
>          completeDescriptor (?);
> 
> }
> 
> the ? indicates with what status I should complete the descriptor? I 
> would probably need to iterate over all the descriptor's buffer status 
> to see if any of the (previous)buffer has failed to set error status on 
> the descriptor overall? I think so, we would still need a look up loop 
> here, I can't see deciphering this from the map.

Can we record a post-processing status in the descriptor, setting it to
success when constructor, and setting it to error when a post-processing
fails ? Then you can inspect that state only when completing the
request. A boolean flag (hasPostProcessingErrors for instance) could be
enough.

Or we could reuse the status_ member variable for that. It's currently
used both to tell if a descriptor is complete (when !pending) and what
its status is. We could split that into a status flag that would only
have success and error values, and a pending (or complete) boolean. This
may be a better design, as it would allow us to update the request
status as soon as an error is detected, and set the completion flag
separately only when all processing has completed.

> Are we getting too complicated with this? I have started to feel so ...
> 
> > Other designs may be possible.
> >
> >>   	}
> >>   
> >> +	if (needsPostProcessing) {
> >> +		if (processingStatus == Camera3RequestDescriptor::Status::Error) {
> >> +			descriptor->status_ = processingStatus;
> >> +			sendCaptureResults();
> >> +		}
> >> +
> >> +		return;
> >> +	}
> >> +
> >>   	descriptor->status_ = Camera3RequestDescriptor::Status::Success;
> >>   	sendCaptureResults();
> >>   }
> >> @@ -1206,6 +1220,64 @@ void CameraDevice::sendCaptureResults()
> >>   	}
> >>   }
> >>   
> >> +void CameraDevice::setBufferStatus(CameraStream *cameraStream,
> >> +				   Camera3RequestDescriptor::StreamBuffer &buffer,
> >> +				   Camera3RequestDescriptor *request,
> >> +				   Camera3RequestDescriptor::Status status)
> >> +{
> >> +	/*
> >> +	 * Return the FrameBuffer to the CameraStream now that we're
> >> +	 * done processing it.
> >> +	 */
> >> +	if (cameraStream->type() == CameraStream::Type::Internal)
> >> +		cameraStream->putBuffer(buffer.internalBuffer);
> >> +
> >> +	buffer.status = status;
> >> +	if (status != Camera3RequestDescriptor::Status::Success)
> >> +		notifyError(request->frameNumber_, buffer.stream->camera3Stream(),
> >>   +			    CAMERA3_MSG_ERROR_BUFFER);
> >> +}
> >> +
> >> +void CameraDevice::streamProcessingComplete(CameraStream *cameraStream,
> >> +					    Camera3RequestDescriptor *request,
> >> +					    Camera3RequestDescriptor::Status status)
> >> +{
> >> +	MutexLocker locker(request->streamsProcessMutex_);
> >> +	for (auto &buffer : request->buffers_) {
> >> +		if (buffer.stream != cameraStream)
> >> +			continue;
> >> +
> >> +		setBufferStatus(cameraStream, buffer, request, status);
> >> +	}
> >> +
> >> +	bool hasPostProcessingErrors = false;
> >> +	for (auto &buffer : request->buffers_) {
> >> +		if (cameraStream->type() == CameraStream::Type::Direct)
> >> +			continue;
> >> +
> >> +		/*
> >> +		 * Other eligible buffers might be waiting to get post-processed.
> >> +		 * So wait for their turn before sendCaptureResults() for the
> >> +		 * descriptor.
> >> +		 */
> >> +		if (buffer.status == Camera3RequestDescriptor::Status::Pending)
> >> +			return;
> >> +
> >> +		if (!hasPostProcessingErrors &&
> >> +		    buffer.status == Camera3RequestDescriptor::Status::Error)
> >> +			hasPostProcessingErrors = true;
> >> +	}
> >> +
> >> +	if (hasPostProcessingErrors)
> >> +		request->status_ = Camera3RequestDescriptor::Status::Error;
> >> +	else
> >> +		request->status_ = Camera3RequestDescriptor::Status::Success;
> >> +
> >> +	locker.unlock();
> >> +
> >> +	sendCaptureResults();
> >> +}
> >> +
> >>   std::string CameraDevice::logPrefix() const
> >>   {
> >>   	return "'" + camera_->id() + "'";
> >> diff --git a/src/android/camera_device.h b/src/android/camera_device.h
> >> index 863cf414..1ef933da 100644
> >> --- a/src/android/camera_device.h
> >> +++ b/src/android/camera_device.h
> >> @@ -66,6 +66,9 @@ public:
> >>   	int configureStreams(camera3_stream_configuration_t *stream_list);
> >>   	int processCaptureRequest(camera3_capture_request_t *request);
> >>   	void requestComplete(libcamera::Request *request);
> >> +	void streamProcessingComplete(CameraStream *cameraStream,
> >> +				      Camera3RequestDescriptor *request,
> >> +				      Camera3RequestDescriptor::Status status);
> >>   
> >>   protected:
> >>   	std::string logPrefix() const override;
> >> @@ -94,6 +97,10 @@ private:
> >>   			 camera3_error_msg_code code) const;
> >>   	int processControls(Camera3RequestDescriptor *descriptor);
> >>   	void sendCaptureResults();
> >> +	void setBufferStatus(CameraStream *cameraStream,
> >> +			     Camera3RequestDescriptor::StreamBuffer &buffer,
> >> +			     Camera3RequestDescriptor *request,
> >> +			     Camera3RequestDescriptor::Status status);
> >>   	std::unique_ptr<CameraMetadata> getResultMetadata(
> >>   		const Camera3RequestDescriptor &descriptor) const;
> >>   
> >> diff --git a/src/android/camera_request.h b/src/android/camera_request.h
> >> index 05dabf89..3a2774e0 100644
> >> --- a/src/android/camera_request.h
> >> +++ b/src/android/camera_request.h
> >> @@ -8,6 +8,7 @@
> >>   #define __ANDROID_CAMERA_REQUEST_H__
> >>   
> >>   #include <memory>
> >> +#include <mutex>
> >>   #include <vector>
> >>   
> >>   #include <libcamera/base/class.h>
> >> @@ -37,6 +38,7 @@ public:
> >>   		std::unique_ptr<libcamera::FrameBuffer> frameBuffer;
> >>   		int fence;
> >>   		Status status;
> >> +		libcamera::FrameBuffer *internalBuffer = nullptr;
> >>   	};
> >>   
> >>   	Camera3RequestDescriptor(libcamera::Camera *camera,
> >> @@ -47,6 +49,8 @@ public:
> >>   
> >>   	uint32_t frameNumber_ = 0;
> >>   
> >> +	/* Protects buffers_ for post-processing streams. */
> >> +	std::mutex streamsProcessMutex_;
> >>   	std::vector<StreamBuffer> buffers_;
> >>   
> >>   	CameraMetadata settings_;
> >> diff --git a/src/android/camera_stream.cpp b/src/android/camera_stream.cpp
> >> index f44a2717..04cbef8c 100644
> >> --- a/src/android/camera_stream.cpp
> >> +++ b/src/android/camera_stream.cpp
> >> @@ -22,6 +22,7 @@
> >>   #include "camera_capabilities.h"
> >>   #include "camera_device.h"
> >>   #include "camera_metadata.h"
> >> +#include "post_processor.h"
> >>   
> >>   using namespace libcamera;
> >>   
> >> @@ -97,6 +98,18 @@ int CameraStream::configure()
> >>   		int ret = postProcessor_->configure(configuration(), output);
> >>   		if (ret)
> >>   			return ret;
> >> +
> >> +		postProcessor_->processComplete.connect(
> >> +			this, [&](Camera3RequestDescriptor *request, PostProcessor::Status status) {
> >> +				Camera3RequestDescriptor::Status bufferStatus =
> >> +					Camera3RequestDescriptor::Status::Error;
> >> +
> >> +				if (status == PostProcessor::Status::Success)
> >> +					bufferStatus = Camera3RequestDescriptor::Status::Success;
> >
> > It looks weird to make Error a default (and thus special) case. Would
> > any of the following be better ?
> >
> > 				Camera3RequestDescriptor::Status bufferStatus;
> >
> > 				if (status == PostProcessor::Status::Success)
> > 					bufferStatus = Camera3RequestDescriptor::Status::Success;
> > 				else
> > 					bufferStatus = Camera3RequestDescriptor::Status::Error;
> >
> >
> > 				Camera3RequestDescriptor::Status bufferStatus =
> > 					status == PostProcessor::Status::Success ?
> > 					Camera3RequestDescriptor::Status::Success :
> > 					Camera3RequestDescriptor::Status::Error;
> >
> > I think I like the second option best.
> >
> >> +
> >> +				cameraDevice_->streamProcessingComplete(this, request,
> >> +									bufferStatus);
> >> +			});
> >>   	}
> >>   
> >>   	if (type_ == Type::Internal) {
> >> diff --git a/src/android/jpeg/post_processor_jpeg.cpp b/src/android/jpeg/post_processor_jpeg.cpp
> >> index 699576ef..a001fede 100644
> >> --- a/src/android/jpeg/post_processor_jpeg.cpp
> >> +++ b/src/android/jpeg/post_processor_jpeg.cpp
> >> @@ -198,6 +198,7 @@ int PostProcessorJpeg::process(const FrameBuffer &source,
> >>   					 exif.data(), quality);
> >>   	if (jpeg_size < 0) {
> >>   		LOG(JPEG, Error) << "Failed to encode stream image";
> >> +		processComplete.emit(request, PostProcessor::Status::Error);
> >
> > I think you can write Status::Error here and below, including in
> > post_processor_yuv.cpp (not above in camera_stream.cpp though).
> >
> >>   		return jpeg_size;
> >>   	}
> >>   
> >> @@ -211,6 +212,7 @@ int PostProcessorJpeg::process(const FrameBuffer &source,
> >>   
> >>   	/* Update the JPEG result Metadata. */
> >>   	resultMetadata->addEntry(ANDROID_JPEG_SIZE, jpeg_size);
> >> +	processComplete.emit(request, PostProcessor::Status::Success);
> >>   
> >>   	return 0;
> >>   }
> >> diff --git a/src/android/post_processor.h b/src/android/post_processor.h
> >> index 27eaef88..14f5e8c7 100644
> >> --- a/src/android/post_processor.h
> >> +++ b/src/android/post_processor.h
> >> @@ -7,6 +7,8 @@
> >>   #ifndef __ANDROID_POST_PROCESSOR_H__
> >>   #define __ANDROID_POST_PROCESSOR_H__
> >>   
> >> +#include <libcamera/base/signal.h>
> >> +
> >>   #include <libcamera/framebuffer.h>
> >>   #include <libcamera/stream.h>
> >>   
> >> @@ -17,6 +19,11 @@ class Camera3RequestDescriptor;
> >>   class PostProcessor
> >>   {
> >>   public:
> >> +	enum class Status {
> >> +		Error,
> >> +		Success
> >> +	};
> >> +
> >>   	virtual ~PostProcessor() = default;
> >>   
> >>   	virtual int configure(const libcamera::StreamConfiguration &inCfg,
> >> @@ -24,6 +31,8 @@ public:
> >>   	virtual int process(const libcamera::FrameBuffer &source,
> >>   			    CameraBuffer *destination,
> >>   			    Camera3RequestDescriptor *request) = 0;
> >> +
> >> +	libcamera::Signal<Camera3RequestDescriptor *, Status> processComplete;
> >>   };
> >>   
> >>   #endif /* __ANDROID_POST_PROCESSOR_H__ */
> >> diff --git a/src/android/yuv/post_processor_yuv.cpp b/src/android/yuv/post_processor_yuv.cpp
> >> index 8110a1f1..fd364741 100644
> >> --- a/src/android/yuv/post_processor_yuv.cpp
> >> +++ b/src/android/yuv/post_processor_yuv.cpp
> >> @@ -51,14 +51,17 @@ int PostProcessorYuv::configure(const StreamConfiguration &inCfg,
> >>   
> >>   int PostProcessorYuv::process(const FrameBuffer &source,
> >>   			      CameraBuffer *destination,
> >> -			      [[maybe_unused]] Camera3RequestDescriptor *request)
> >> +			      Camera3RequestDescriptor *request)
> >>   {
> >> -	if (!isValidBuffers(source, *destination))
> >> +	if (!isValidBuffers(source, *destination)) {
> >> +		processComplete.emit(request, PostProcessor::Status::Error);
> >>   		return -EINVAL;
> >> +	}
> >>   
> >>   	const MappedFrameBuffer sourceMapped(&source, MappedFrameBuffer::MapFlag::Read);
> >>   	if (!sourceMapped.isValid()) {
> >>   		LOG(YUV, Error) << "Failed to mmap camera frame buffer";
> >> +		processComplete.emit(request, PostProcessor::Status::Error);
> >>   		return -EINVAL;
> >>   	}
> >>   
> >> @@ -76,9 +79,12 @@ int PostProcessorYuv::process(const FrameBuffer &source,
> >>   				    libyuv::FilterMode::kFilterBilinear);
> >>   	if (ret) {
> >>   		LOG(YUV, Error) << "Failed NV12 scaling: " << ret;
> >> +		processComplete.emit(request, PostProcessor::Status::Error);
> >>   		return -EINVAL;
> >>   	}
> >>   
> >> +	processComplete.emit(request, PostProcessor::Status::Success);
> >> +
> >>   	return 0;
> >>   }
> >>

Hi Laurent,

On 10/21/21 7:22 PM, Laurent Pinchart wrote:
> Hi Umang,
>
> On Thu, Oct 21, 2021 at 11:05:44AM +0530, Umang Jain wrote:
>> On 10/21/21 6:01 AM, Laurent Pinchart wrote:
>>> On Wed, Oct 20, 2021 at 04:12:09PM +0530, Umang Jain wrote:
>>>> Notify that the post processing for a request has been completed,
>>>> via a signal. A pointer to the descriptor which is tracking the
>>>> capture request is emitted along with the status of post processed
>>>> buffer. The function CameraDevice::streamProcessingComplete() will
>>>> finally set the status on the request descriptor and send capture
>>>> results back to the framework accordingly.
>>>>
>>>> We also need to save a pointer to any internal buffers that might have
>>>> been allocated by CameraStream. The buffer should be returned back to
>>>> CameraStream just before capture results are sent.
>>>>
>>>> A streamProcessMutex_ has been introduced here itself, which will be
>>> Did you mean s/itself/as well/ ?
>>>
>>>> applicable to guard access to descriptor->buffers_ when post-processing
>>>> is moved to be asynchronous in subsequent commits.
>>>>
>>>> Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
>>>> ---
>>>>    src/android/camera_device.cpp            | 92 +++++++++++++++++++++---
>>>>    src/android/camera_device.h              |  7 ++
>>>>    src/android/camera_request.h             |  4 ++
>>>>    src/android/camera_stream.cpp            | 13 ++++
>>>>    src/android/jpeg/post_processor_jpeg.cpp |  2 +
>>>>    src/android/post_processor.h             |  9 +++
>>>>    src/android/yuv/post_processor_yuv.cpp   | 10 ++-
>>>>    7 files changed, 125 insertions(+), 12 deletions(-)
>>>>
>>>> diff --git a/src/android/camera_device.cpp b/src/android/camera_device.cpp
>>>> index 806b4090..541c2c81 100644
>>>> --- a/src/android/camera_device.cpp
>>>> +++ b/src/android/camera_device.cpp
>>>> @@ -1117,6 +1117,15 @@ void CameraDevice::requestComplete(Request *request)
>>>>    	}
>>>>    
>>>>    	/* Handle post-processing. */
>>>> +	bool needsPostProcessing = false;
>>>> +	Camera3RequestDescriptor::Status processingStatus =
>>>> +		Camera3RequestDescriptor::Status::Pending;
>>>> +	/*
>>>> +	 * \todo Apply streamsProcessMutex_ when post-processing is adapted to run
>>>> +	 * asynchronously. If we introduce the streamsProcessMutex_ right away, the
>>>> +	 * lock will be held forever since it is synchronous at this point
>>>> +	 * (see streamProcessingComplete).
>>>> +	 */
>>>>    	for (auto &buffer : descriptor->buffers_) {
>>>>    		CameraStream *stream = buffer.stream;
>>>>    
>>>> @@ -1132,22 +1141,27 @@ void CameraDevice::requestComplete(Request *request)
>>>>    			continue;
>>>>    		}
>>>>    
>>>> -		int ret = stream->process(*src, buffer, descriptor);
>>>> -
>>>> -		/*
>>>> -		 * Return the FrameBuffer to the CameraStream now that we're
>>>> -		 * done processing it.
>>>> -		 */
>>>>    		if (stream->type() == CameraStream::Type::Internal)
>>>> -			stream->putBuffer(src);
>>>> +			buffer.internalBuffer = src;
>>> Let's make the field name more self-explanatory. A possible candidate is
>>> sourceBuffer instead of internalBuffer.
>>>
>>> Could we do this in CameraDevice::processCaptureRequest(), just after
>>> calling cameraStream->getBuffer() ? I'll feel less worried about a leak
>>> if we store the buffer for later release right after acquiring it.
>> Ack.
>>
>>>>    
>>>> +		needsPostProcessing = true;
>>>> +		int ret = stream->process(*src, buffer, descriptor);
>>>>    		if (ret) {
>>>> -			buffer.status = Camera3RequestDescriptor::Status::Error;
>>>> -			notifyError(descriptor->frameNumber_, stream->camera3Stream(),
>>>> -				    CAMERA3_MSG_ERROR_BUFFER);
>>>> +			setBufferStatus(stream, buffer, descriptor,
>>>> +					Camera3RequestDescriptor::Status::Error);
>>>> +			processingStatus = Camera3RequestDescriptor::Status::Error;
>>>>    		}
>>> I think we need to improve error handling a little bit, in order to
>>> support multiple streams being post-processed. We need to complete the
>>> request in CameraDevice::streamProcessingComplete() when the last
>>> processing stream completes, so the number of post-processed streams
>>> need to be somehow recorded in the Camera3RequestDescriptor. It could be
>>> tempted to have a counter, but a
>> I have implemented a counter based solution, it still didn't address all
>> the corner cases. Since we have two  path of error handling (synchronous
>> error and asynchronous error), a counter based implementation was
>> probably too verbose with much of code duplication to handle various
>> scenarios.
>>
>>> 	std::map<CameraStream *, StreamBuffer *> pendingPostProcess_;
>>>
>>> could be better, as it will also remove the need for loops in
>>> streamProcessingComplete() to lookup the buffer from the stream and to
>>> check if the request has been fully processed. Accessing the map has to
>>> be done with the mutex held to avoid race conditions, but it's a bit
>>> more tricky than that. If we just add elements to the map here, we could
>> Good, so you do understand so many looping lookups in
>> streamProcessingComplete.
>>
>> I broadly feel okay with std::map<CameraStream *, StreamBuffer *>
>> pendingPostProcess_; as long as it resides inside the descriptor. For
>> me, it avoids lookups, and can address the \todo in 3/4.
>>
>> Having said that, I feel a bit wary of introducing more data structures
>> for management. We already have a queue of post-processing (convert to
>> std:deque if we want to access the queued requests for post-processing)
>> and now we will have another map to tracking the requests. I wonder if
>> we can get away with a PostProcessorWorker's std::deque, with the
>> benefits of the map. But again, we have to take care of exposure / mutex
>> with main thread, which can lead to subtle bugs and unwanted waiting on
>> each thread
>>
>> Now I think about it, the pendingPostProcess_ map is about Stream's
>> pending processing _per descriptor_, whereas the PostProcessorWorker's
>> queue is replacement for Thread's message queue. Hmm.
> That's right, those two data structures are independent from each other.
>
>>> race with streamProcessingComplete() as it could be called for the first
>>> post-processed stream before we have a chance to add the second one
>>> here. streamProcessingComplete() would then incorrectly think it has
>>> completed the last stream, and proceed to complete the request.
>>>
>>> This race could be solved by holding the lock for the whole duration of
>>> the loop here, covering all calls to stream->process(), but it may be
>> Yes,  I am considering this in current implementation too. The way it
>> will look like, is first queue up all the post-processing requests to
>> PostProcessorWoe, only then, allow any of the
>> slot(streamProcessingComplete) to get executed. A simple mutex hold can
>> do that
> I usually try to minimize the amount of code covered by locks, and focus
> on data access only if possible instead of keeping the lock held over
> the callbacks. Let's see if that's possible. There's a tricky part
> though, as sendCaptureResults() is called from two different threads
> (synchronously with request queuing in error paths and asynchronously in
> the completion path), we currently have a race condition.
>
> Thread A							Thread B
> -----------------------------------------------------------------------------------------------------------
>
> MutexLocker lock(descriptorsMutex_);
> while (!descriptors_.empty() &&
>         !descriptors_.front()->isPending()) {
>          auto descriptor = std::move(descriptors_.front());
>          descriptors_.pop();
>
>          lock.unlock();
> 								MutexLocker lock(descriptorsMutex_);
> 								while (!descriptors_.empty() &&
> 								       !descriptors_.front()->isPending()) {
> 									auto descriptor = std::move(descriptors_.front());
> 									descriptors_.pop();
>
> 									lock.unlock();
>
> 									...
>
> 									callbacks_->process_capture_result(callbacks_,
> 													   &captureResult);
>
> 									lock.lock();
> 								}
> 	...
>
>          callbacks_->process_capture_result(callbacks_,
> 					   &captureResult);
>
>          lock.lock();
> }
>
> Thread A gets the request at the top of the queue, thread B gets the
> next one, and signals its completion before thread A.
>
> It's likely possible to implement something clever here, to minimize the
> locked sections and still be correct, but that may be unnecessary
> optimization. We could start by holding the lock for the whole duration
> of the function. In that case, I would remove the lock from
> sendCaptureResults() completely, and call the function with the lock
> held in completeDescriptor().


Yes, provided sendCaptureResults() is only called completeDescriptor(). 
I don't want to get a implementation which uses completeDescriptor() and 
sendCaptureResults() both for process_capture_result() callback.

>
>>> possible to do better. We could add entries to the map in
>>> processCaptureRequest() instead. We would need, here, to remove entries
>> I am not so sure about this, We could add entries in
>> processCaptureRequest() but it feels too early. Let me try to address
>> other comments, and I can iterate on this on top.
>>
>>> from the map if stream->process() fails, and complete the request if we
>>> remove the last entry (as otherwise, streamProcessingComplete() could
>>> complete all streams, then the last stream->process() call could fail,
>>> and nobody would complete the request).
>> This is still a bit tricky to handle. What's the de-facto criteria to
>> remove entries from the map (not just the error path) ?
>>
>> Assuming we hold the lock for entire duration of
>>
>>       Locker.lock();
>>
>>       for {
>>           ...
>>           int ret = stream->process(...);
>>           if (ret) {
>>               descriptor.pendingPostProcess_.erase(stream);
>>               setBufferStatus(stream, error);
>>
>>               if (descriptor.pendingPostProcess_.size() == 0)
>>                   completeDescriptor (error);
>>
>>           }
>>
>>       }
>>       locker.unlock();
>>
>> ....
>>
>> streamProcessingComplete(..., bufferStatus)
>>
>> {
>>
>>       Locker.lock();
>>
>> descriptor.pendingPostProcess_.erase(stream);
>>       setBufferStatus(stream, bufferStatus);
>>
>>       if (descriptor.pendingPostProcess_.size() == 0)
>>           completeDescriptor (?);
>>
>> }
>>
>> the ? indicates with what status I should complete the descriptor? I
>> would probably need to iterate over all the descriptor's buffer status
>> to see if any of the (previous)buffer has failed to set error status on
>> the descriptor overall? I think so, we would still need a look up loop
>> here, I can't see deciphering this from the map.
> Can we record a post-processing status in the descriptor, setting it to
> success when constructor, and setting it to error when a post-processing
> fails ? Then you can inspect that state only when completing the
> request. A boolean flag (hasPostProcessingErrors for instance) could be
> enough.


I would take the boolean flag approach for now.

>
> Or we could reuse the status_ member variable for that. It's currently
> used both to tell if a descriptor is complete (when !pending) and what
> its status is. We could split that into a status flag that would only
> have success and error values, and a pending (or complete) boolean. This
> may be a better design, as it would allow us to update the request
> status as soon as an error is detected, and set the completion flag
> separately only when all processing has completed.


This is sane, which in interest of not increasing further scope of the 
series, I am tempted to address this on top. I can record it with a \todo

>
>> Are we getting too complicated with this? I have started to feel so ...
>>
>>> Other designs may be possible.
>>>
>>>>    	}
>>>>    
>>>> +	if (needsPostProcessing) {
>>>> +		if (processingStatus == Camera3RequestDescriptor::Status::Error) {
>>>> +			descriptor->status_ = processingStatus;
>>>> +			sendCaptureResults();
>>>> +		}
>>>> +
>>>> +		return;
>>>> +	}
>>>> +
>>>>    	descriptor->status_ = Camera3RequestDescriptor::Status::Success;
>>>>    	sendCaptureResults();
>>>>    }
>>>> @@ -1206,6 +1220,64 @@ void CameraDevice::sendCaptureResults()
>>>>    	}
>>>>    }
>>>>    
>>>> +void CameraDevice::setBufferStatus(CameraStream *cameraStream,
>>>> +				   Camera3RequestDescriptor::StreamBuffer &buffer,
>>>> +				   Camera3RequestDescriptor *request,
>>>> +				   Camera3RequestDescriptor::Status status)
>>>> +{
>>>> +	/*
>>>> +	 * Return the FrameBuffer to the CameraStream now that we're
>>>> +	 * done processing it.
>>>> +	 */
>>>> +	if (cameraStream->type() == CameraStream::Type::Internal)
>>>> +		cameraStream->putBuffer(buffer.internalBuffer);
>>>> +
>>>> +	buffer.status = status;
>>>> +	if (status != Camera3RequestDescriptor::Status::Success)
>>>> +		notifyError(request->frameNumber_, buffer.stream->camera3Stream(),
>>>>    +			    CAMERA3_MSG_ERROR_BUFFER);
>>>> +}
>>>> +
>>>> +void CameraDevice::streamProcessingComplete(CameraStream *cameraStream,
>>>> +					    Camera3RequestDescriptor *request,
>>>> +					    Camera3RequestDescriptor::Status status)
>>>> +{
>>>> +	MutexLocker locker(request->streamsProcessMutex_);
>>>> +	for (auto &buffer : request->buffers_) {
>>>> +		if (buffer.stream != cameraStream)
>>>> +			continue;
>>>> +
>>>> +		setBufferStatus(cameraStream, buffer, request, status);
>>>> +	}
>>>> +
>>>> +	bool hasPostProcessingErrors = false;
>>>> +	for (auto &buffer : request->buffers_) {
>>>> +		if (cameraStream->type() == CameraStream::Type::Direct)
>>>> +			continue;
>>>> +
>>>> +		/*
>>>> +		 * Other eligible buffers might be waiting to get post-processed.
>>>> +		 * So wait for their turn before sendCaptureResults() for the
>>>> +		 * descriptor.
>>>> +		 */
>>>> +		if (buffer.status == Camera3RequestDescriptor::Status::Pending)
>>>> +			return;
>>>> +
>>>> +		if (!hasPostProcessingErrors &&
>>>> +		    buffer.status == Camera3RequestDescriptor::Status::Error)
>>>> +			hasPostProcessingErrors = true;
>>>> +	}
>>>> +
>>>> +	if (hasPostProcessingErrors)
>>>> +		request->status_ = Camera3RequestDescriptor::Status::Error;
>>>> +	else
>>>> +		request->status_ = Camera3RequestDescriptor::Status::Success;
>>>> +
>>>> +	locker.unlock();
>>>> +
>>>> +	sendCaptureResults();
>>>> +}
>>>> +
>>>>    std::string CameraDevice::logPrefix() const
>>>>    {
>>>>    	return "'" + camera_->id() + "'";
>>>> diff --git a/src/android/camera_device.h b/src/android/camera_device.h
>>>> index 863cf414..1ef933da 100644
>>>> --- a/src/android/camera_device.h
>>>> +++ b/src/android/camera_device.h
>>>> @@ -66,6 +66,9 @@ public:
>>>>    	int configureStreams(camera3_stream_configuration_t *stream_list);
>>>>    	int processCaptureRequest(camera3_capture_request_t *request);
>>>>    	void requestComplete(libcamera::Request *request);
>>>> +	void streamProcessingComplete(CameraStream *cameraStream,
>>>> +				      Camera3RequestDescriptor *request,
>>>> +				      Camera3RequestDescriptor::Status status);
>>>>    
>>>>    protected:
>>>>    	std::string logPrefix() const override;
>>>> @@ -94,6 +97,10 @@ private:
>>>>    			 camera3_error_msg_code code) const;
>>>>    	int processControls(Camera3RequestDescriptor *descriptor);
>>>>    	void sendCaptureResults();
>>>> +	void setBufferStatus(CameraStream *cameraStream,
>>>> +			     Camera3RequestDescriptor::StreamBuffer &buffer,
>>>> +			     Camera3RequestDescriptor *request,
>>>> +			     Camera3RequestDescriptor::Status status);
>>>>    	std::unique_ptr<CameraMetadata> getResultMetadata(
>>>>    		const Camera3RequestDescriptor &descriptor) const;
>>>>    
>>>> diff --git a/src/android/camera_request.h b/src/android/camera_request.h
>>>> index 05dabf89..3a2774e0 100644
>>>> --- a/src/android/camera_request.h
>>>> +++ b/src/android/camera_request.h
>>>> @@ -8,6 +8,7 @@
>>>>    #define __ANDROID_CAMERA_REQUEST_H__
>>>>    
>>>>    #include <memory>
>>>> +#include <mutex>
>>>>    #include <vector>
>>>>    
>>>>    #include <libcamera/base/class.h>
>>>> @@ -37,6 +38,7 @@ public:
>>>>    		std::unique_ptr<libcamera::FrameBuffer> frameBuffer;
>>>>    		int fence;
>>>>    		Status status;
>>>> +		libcamera::FrameBuffer *internalBuffer = nullptr;
>>>>    	};
>>>>    
>>>>    	Camera3RequestDescriptor(libcamera::Camera *camera,
>>>> @@ -47,6 +49,8 @@ public:
>>>>    
>>>>    	uint32_t frameNumber_ = 0;
>>>>    
>>>> +	/* Protects buffers_ for post-processing streams. */
>>>> +	std::mutex streamsProcessMutex_;
>>>>    	std::vector<StreamBuffer> buffers_;
>>>>    
>>>>    	CameraMetadata settings_;
>>>> diff --git a/src/android/camera_stream.cpp b/src/android/camera_stream.cpp
>>>> index f44a2717..04cbef8c 100644
>>>> --- a/src/android/camera_stream.cpp
>>>> +++ b/src/android/camera_stream.cpp
>>>> @@ -22,6 +22,7 @@
>>>>    #include "camera_capabilities.h"
>>>>    #include "camera_device.h"
>>>>    #include "camera_metadata.h"
>>>> +#include "post_processor.h"
>>>>    
>>>>    using namespace libcamera;
>>>>    
>>>> @@ -97,6 +98,18 @@ int CameraStream::configure()
>>>>    		int ret = postProcessor_->configure(configuration(), output);
>>>>    		if (ret)
>>>>    			return ret;
>>>> +
>>>> +		postProcessor_->processComplete.connect(
>>>> +			this, [&](Camera3RequestDescriptor *request, PostProcessor::Status status) {
>>>> +				Camera3RequestDescriptor::Status bufferStatus =
>>>> +					Camera3RequestDescriptor::Status::Error;
>>>> +
>>>> +				if (status == PostProcessor::Status::Success)
>>>> +					bufferStatus = Camera3RequestDescriptor::Status::Success;
>>> It looks weird to make Error a default (and thus special) case. Would
>>> any of the following be better ?
>>>
>>> 				Camera3RequestDescriptor::Status bufferStatus;
>>>
>>> 				if (status == PostProcessor::Status::Success)
>>> 					bufferStatus = Camera3RequestDescriptor::Status::Success;
>>> 				else
>>> 					bufferStatus = Camera3RequestDescriptor::Status::Error;
>>>
>>>
>>> 				Camera3RequestDescriptor::Status bufferStatus =
>>> 					status == PostProcessor::Status::Success ?
>>> 					Camera3RequestDescriptor::Status::Success :
>>> 					Camera3RequestDescriptor::Status::Error;
>>>
>>> I think I like the second option best.
>>>
>>>> +
>>>> +				cameraDevice_->streamProcessingComplete(this, request,
>>>> +									bufferStatus);
>>>> +			});
>>>>    	}
>>>>    
>>>>    	if (type_ == Type::Internal) {
>>>> diff --git a/src/android/jpeg/post_processor_jpeg.cpp b/src/android/jpeg/post_processor_jpeg.cpp
>>>> index 699576ef..a001fede 100644
>>>> --- a/src/android/jpeg/post_processor_jpeg.cpp
>>>> +++ b/src/android/jpeg/post_processor_jpeg.cpp
>>>> @@ -198,6 +198,7 @@ int PostProcessorJpeg::process(const FrameBuffer &source,
>>>>    					 exif.data(), quality);
>>>>    	if (jpeg_size < 0) {
>>>>    		LOG(JPEG, Error) << "Failed to encode stream image";
>>>> +		processComplete.emit(request, PostProcessor::Status::Error);
>>> I think you can write Status::Error here and below, including in
>>> post_processor_yuv.cpp (not above in camera_stream.cpp though).
>>>
>>>>    		return jpeg_size;
>>>>    	}
>>>>    
>>>> @@ -211,6 +212,7 @@ int PostProcessorJpeg::process(const FrameBuffer &source,
>>>>    
>>>>    	/* Update the JPEG result Metadata. */
>>>>    	resultMetadata->addEntry(ANDROID_JPEG_SIZE, jpeg_size);
>>>> +	processComplete.emit(request, PostProcessor::Status::Success);
>>>>    
>>>>    	return 0;
>>>>    }
>>>> diff --git a/src/android/post_processor.h b/src/android/post_processor.h
>>>> index 27eaef88..14f5e8c7 100644
>>>> --- a/src/android/post_processor.h
>>>> +++ b/src/android/post_processor.h
>>>> @@ -7,6 +7,8 @@
>>>>    #ifndef __ANDROID_POST_PROCESSOR_H__
>>>>    #define __ANDROID_POST_PROCESSOR_H__
>>>>    
>>>> +#include <libcamera/base/signal.h>
>>>> +
>>>>    #include <libcamera/framebuffer.h>
>>>>    #include <libcamera/stream.h>
>>>>    
>>>> @@ -17,6 +19,11 @@ class Camera3RequestDescriptor;
>>>>    class PostProcessor
>>>>    {
>>>>    public:
>>>> +	enum class Status {
>>>> +		Error,
>>>> +		Success
>>>> +	};
>>>> +
>>>>    	virtual ~PostProcessor() = default;
>>>>    
>>>>    	virtual int configure(const libcamera::StreamConfiguration &inCfg,
>>>> @@ -24,6 +31,8 @@ public:
>>>>    	virtual int process(const libcamera::FrameBuffer &source,
>>>>    			    CameraBuffer *destination,
>>>>    			    Camera3RequestDescriptor *request) = 0;
>>>> +
>>>> +	libcamera::Signal<Camera3RequestDescriptor *, Status> processComplete;
>>>>    };
>>>>    
>>>>    #endif /* __ANDROID_POST_PROCESSOR_H__ */
>>>> diff --git a/src/android/yuv/post_processor_yuv.cpp b/src/android/yuv/post_processor_yuv.cpp
>>>> index 8110a1f1..fd364741 100644
>>>> --- a/src/android/yuv/post_processor_yuv.cpp
>>>> +++ b/src/android/yuv/post_processor_yuv.cpp
>>>> @@ -51,14 +51,17 @@ int PostProcessorYuv::configure(const StreamConfiguration &inCfg,
>>>>    
>>>>    int PostProcessorYuv::process(const FrameBuffer &source,
>>>>    			      CameraBuffer *destination,
>>>> -			      [[maybe_unused]] Camera3RequestDescriptor *request)
>>>> +			      Camera3RequestDescriptor *request)
>>>>    {
>>>> -	if (!isValidBuffers(source, *destination))
>>>> +	if (!isValidBuffers(source, *destination)) {
>>>> +		processComplete.emit(request, PostProcessor::Status::Error);
>>>>    		return -EINVAL;
>>>> +	}
>>>>    
>>>>    	const MappedFrameBuffer sourceMapped(&source, MappedFrameBuffer::MapFlag::Read);
>>>>    	if (!sourceMapped.isValid()) {
>>>>    		LOG(YUV, Error) << "Failed to mmap camera frame buffer";
>>>> +		processComplete.emit(request, PostProcessor::Status::Error);
>>>>    		return -EINVAL;
>>>>    	}
>>>>    
>>>> @@ -76,9 +79,12 @@ int PostProcessorYuv::process(const FrameBuffer &source,
>>>>    				    libyuv::FilterMode::kFilterBilinear);
>>>>    	if (ret) {
>>>>    		LOG(YUV, Error) << "Failed NV12 scaling: " << ret;
>>>> +		processComplete.emit(request, PostProcessor::Status::Error);
>>>>    		return -EINVAL;
>>>>    	}
>>>>    
>>>> +	processComplete.emit(request, PostProcessor::Status::Success);
>>>> +
>>>>    	return 0;
>>>>    }
>>>>

Hi Umang,

On Thu, Oct 21, 2021 at 08:04:18PM +0530, Umang Jain wrote:
> On 10/21/21 7:22 PM, Laurent Pinchart wrote:
> > On Thu, Oct 21, 2021 at 11:05:44AM +0530, Umang Jain wrote:
> >> On 10/21/21 6:01 AM, Laurent Pinchart wrote:
> >>> On Wed, Oct 20, 2021 at 04:12:09PM +0530, Umang Jain wrote:
> >>>> Notify that the post processing for a request has been completed,
> >>>> via a signal. A pointer to the descriptor which is tracking the
> >>>> capture request is emitted along with the status of post processed
> >>>> buffer. The function CameraDevice::streamProcessingComplete() will
> >>>> finally set the status on the request descriptor and send capture
> >>>> results back to the framework accordingly.
> >>>>
> >>>> We also need to save a pointer to any internal buffers that might have
> >>>> been allocated by CameraStream. The buffer should be returned back to
> >>>> CameraStream just before capture results are sent.
> >>>>
> >>>> A streamProcessMutex_ has been introduced here itself, which will be
> >>> Did you mean s/itself/as well/ ?
> >>>
> >>>> applicable to guard access to descriptor->buffers_ when post-processing
> >>>> is moved to be asynchronous in subsequent commits.
> >>>>
> >>>> Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
> >>>> ---
> >>>>    src/android/camera_device.cpp            | 92 +++++++++++++++++++++---
> >>>>    src/android/camera_device.h              |  7 ++
> >>>>    src/android/camera_request.h             |  4 ++
> >>>>    src/android/camera_stream.cpp            | 13 ++++
> >>>>    src/android/jpeg/post_processor_jpeg.cpp |  2 +
> >>>>    src/android/post_processor.h             |  9 +++
> >>>>    src/android/yuv/post_processor_yuv.cpp   | 10 ++-
> >>>>    7 files changed, 125 insertions(+), 12 deletions(-)
> >>>>
> >>>> diff --git a/src/android/camera_device.cpp b/src/android/camera_device.cpp
> >>>> index 806b4090..541c2c81 100644
> >>>> --- a/src/android/camera_device.cpp
> >>>> +++ b/src/android/camera_device.cpp
> >>>> @@ -1117,6 +1117,15 @@ void CameraDevice::requestComplete(Request *request)
> >>>>    	}
> >>>>    
> >>>>    	/* Handle post-processing. */
> >>>> +	bool needsPostProcessing = false;
> >>>> +	Camera3RequestDescriptor::Status processingStatus =
> >>>> +		Camera3RequestDescriptor::Status::Pending;
> >>>> +	/*
> >>>> +	 * \todo Apply streamsProcessMutex_ when post-processing is adapted to run
> >>>> +	 * asynchronously. If we introduce the streamsProcessMutex_ right away, the
> >>>> +	 * lock will be held forever since it is synchronous at this point
> >>>> +	 * (see streamProcessingComplete).
> >>>> +	 */
> >>>>    	for (auto &buffer : descriptor->buffers_) {
> >>>>    		CameraStream *stream = buffer.stream;
> >>>>    
> >>>> @@ -1132,22 +1141,27 @@ void CameraDevice::requestComplete(Request *request)
> >>>>    			continue;
> >>>>    		}
> >>>>    
> >>>> -		int ret = stream->process(*src, buffer, descriptor);
> >>>> -
> >>>> -		/*
> >>>> -		 * Return the FrameBuffer to the CameraStream now that we're
> >>>> -		 * done processing it.
> >>>> -		 */
> >>>>    		if (stream->type() == CameraStream::Type::Internal)
> >>>> -			stream->putBuffer(src);
> >>>> +			buffer.internalBuffer = src;
> >>>
> >>> Let's make the field name more self-explanatory. A possible candidate is
> >>> sourceBuffer instead of internalBuffer.
> >>>
> >>> Could we do this in CameraDevice::processCaptureRequest(), just after
> >>> calling cameraStream->getBuffer() ? I'll feel less worried about a leak
> >>> if we store the buffer for later release right after acquiring it.
> >>
> >> Ack.
> >>
> >>>>    
> >>>> +		needsPostProcessing = true;
> >>>> +		int ret = stream->process(*src, buffer, descriptor);
> >>>>    		if (ret) {
> >>>> -			buffer.status = Camera3RequestDescriptor::Status::Error;
> >>>> -			notifyError(descriptor->frameNumber_, stream->camera3Stream(),
> >>>> -				    CAMERA3_MSG_ERROR_BUFFER);
> >>>> +			setBufferStatus(stream, buffer, descriptor,
> >>>> +					Camera3RequestDescriptor::Status::Error);
> >>>> +			processingStatus = Camera3RequestDescriptor::Status::Error;
> >>>>    		}
> >>>
> >>> I think we need to improve error handling a little bit, in order to
> >>> support multiple streams being post-processed. We need to complete the
> >>> request in CameraDevice::streamProcessingComplete() when the last
> >>> processing stream completes, so the number of post-processed streams
> >>> need to be somehow recorded in the Camera3RequestDescriptor. It could be
> >>> tempted to have a counter, but a
> >>
> >> I have implemented a counter based solution, it still didn't address all
> >> the corner cases. Since we have two  path of error handling (synchronous
> >> error and asynchronous error), a counter based implementation was
> >> probably too verbose with much of code duplication to handle various
> >> scenarios.
> >>
> >>> 	std::map<CameraStream *, StreamBuffer *> pendingPostProcess_;
> >>>
> >>> could be better, as it will also remove the need for loops in
> >>> streamProcessingComplete() to lookup the buffer from the stream and to
> >>> check if the request has been fully processed. Accessing the map has to
> >>> be done with the mutex held to avoid race conditions, but it's a bit
> >>> more tricky than that. If we just add elements to the map here, we could
> >>
> >> Good, so you do understand so many looping lookups in
> >> streamProcessingComplete.
> >>
> >> I broadly feel okay with std::map<CameraStream *, StreamBuffer *>
> >> pendingPostProcess_; as long as it resides inside the descriptor. For
> >> me, it avoids lookups, and can address the \todo in 3/4.
> >>
> >> Having said that, I feel a bit wary of introducing more data structures
> >> for management. We already have a queue of post-processing (convert to
> >> std:deque if we want to access the queued requests for post-processing)
> >> and now we will have another map to tracking the requests. I wonder if
> >> we can get away with a PostProcessorWorker's std::deque, with the
> >> benefits of the map. But again, we have to take care of exposure / mutex
> >> with main thread, which can lead to subtle bugs and unwanted waiting on
> >> each thread
> >>
> >> Now I think about it, the pendingPostProcess_ map is about Stream's
> >> pending processing _per descriptor_, whereas the PostProcessorWorker's
> >> queue is replacement for Thread's message queue. Hmm.
> >
> > That's right, those two data structures are independent from each other.
> >
> >>> race with streamProcessingComplete() as it could be called for the first
> >>> post-processed stream before we have a chance to add the second one
> >>> here. streamProcessingComplete() would then incorrectly think it has
> >>> completed the last stream, and proceed to complete the request.
> >>>
> >>> This race could be solved by holding the lock for the whole duration of
> >>> the loop here, covering all calls to stream->process(), but it may be
> >>
> >> Yes,  I am considering this in current implementation too. The way it
> >> will look like, is first queue up all the post-processing requests to
> >> PostProcessorWoe, only then, allow any of the
> >> slot(streamProcessingComplete) to get executed. A simple mutex hold can
> >> do that
> >
> > I usually try to minimize the amount of code covered by locks, and focus
> > on data access only if possible instead of keeping the lock held over
> > the callbacks. Let's see if that's possible. There's a tricky part
> > though, as sendCaptureResults() is called from two different threads
> > (synchronously with request queuing in error paths and asynchronously in
> > the completion path), we currently have a race condition.
> >
> > Thread A							Thread B
> > -----------------------------------------------------------------------------------------------------------
> >
> > MutexLocker lock(descriptorsMutex_);
> > while (!descriptors_.empty() &&
> >         !descriptors_.front()->isPending()) {
> >          auto descriptor = std::move(descriptors_.front());
> >          descriptors_.pop();
> >
> >          lock.unlock();
> > 								MutexLocker lock(descriptorsMutex_);
> > 								while (!descriptors_.empty() &&
> > 								       !descriptors_.front()->isPending()) {
> > 									auto descriptor = std::move(descriptors_.front());
> > 									descriptors_.pop();
> >
> > 									lock.unlock();
> >
> > 									...
> >
> > 									callbacks_->process_capture_result(callbacks_,
> > 													   &captureResult);
> >
> > 									lock.lock();
> > 								}
> > 	...
> >
> >          callbacks_->process_capture_result(callbacks_,
> > 					   &captureResult);
> >
> >          lock.lock();
> > }
> >
> > Thread A gets the request at the top of the queue, thread B gets the
> > next one, and signals its completion before thread A.
> >
> > It's likely possible to implement something clever here, to minimize the
> > locked sections and still be correct, but that may be unnecessary
> > optimization. We could start by holding the lock for the whole duration
> > of the function. In that case, I would remove the lock from
> > sendCaptureResults() completely, and call the function with the lock
> > held in completeDescriptor().
> 
> Yes, provided sendCaptureResults() is only called completeDescriptor().

I think that's the direction we're taking (we could even consider
merging the two functions together, but I'm not sure that would be a
good idea).

> I don't want to get a implementation which uses completeDescriptor() and 
> sendCaptureResults() both for process_capture_result() callback.
> 
> >>> possible to do better. We could add entries to the map in
> >>> processCaptureRequest() instead. We would need, here, to remove entries
> >>
> >> I am not so sure about this, We could add entries in
> >> processCaptureRequest() but it feels too early. Let me try to address
> >> other comments, and I can iterate on this on top.
> >>
> >>> from the map if stream->process() fails, and complete the request if we
> >>> remove the last entry (as otherwise, streamProcessingComplete() could
> >>> complete all streams, then the last stream->process() call could fail,
> >>> and nobody would complete the request).
> >>
> >> This is still a bit tricky to handle. What's the de-facto criteria to
> >> remove entries from the map (not just the error path) ?
> >>
> >> Assuming we hold the lock for entire duration of
> >>
> >>       Locker.lock();
> >>
> >>       for {
> >>           ...
> >>           int ret = stream->process(...);
> >>           if (ret) {
> >>               descriptor.pendingPostProcess_.erase(stream);
> >>               setBufferStatus(stream, error);
> >>
> >>               if (descriptor.pendingPostProcess_.size() == 0)
> >>                   completeDescriptor (error);
> >>
> >>           }
> >>
> >>       }
> >>       locker.unlock();
> >>
> >> ....
> >>
> >> streamProcessingComplete(..., bufferStatus)
> >>
> >> {
> >>
> >>       Locker.lock();
> >>
> >> descriptor.pendingPostProcess_.erase(stream);
> >>       setBufferStatus(stream, bufferStatus);
> >>
> >>       if (descriptor.pendingPostProcess_.size() == 0)
> >>           completeDescriptor (?);
> >>
> >> }
> >>
> >> the ? indicates with what status I should complete the descriptor? I
> >> would probably need to iterate over all the descriptor's buffer status
> >> to see if any of the (previous)buffer has failed to set error status on
> >> the descriptor overall? I think so, we would still need a look up loop
> >> here, I can't see deciphering this from the map.
> >
> > Can we record a post-processing status in the descriptor, setting it to
> > success when constructor, and setting it to error when a post-processing
> > fails ? Then you can inspect that state only when completing the
> > request. A boolean flag (hasPostProcessingErrors for instance) could be
> > enough.
> 
> I would take the boolean flag approach for now.
> 
> > Or we could reuse the status_ member variable for that. It's currently
> > used both to tell if a descriptor is complete (when !pending) and what
> > its status is. We could split that into a status flag that would only
> > have success and error values, and a pending (or complete) boolean. This
> > may be a better design, as it would allow us to update the request
> > status as soon as an error is detected, and set the completion flag
> > separately only when all processing has completed.
> 
> This is sane, which in interest of not increasing further scope of the 
> series, I am tempted to address this on top. I can record it with a \todo

I'm OK with that if you think it would be too disruptive to make this
change at the bottom of the series, but I wonder if the rest wouldn't be
cleaner and clearer if implemented on top of this (hopefully) simple
change.

> >> Are we getting too complicated with this? I have started to feel so ...
> >>
> >>> Other designs may be possible.
> >>>
> >>>>    	}
> >>>>    
> >>>> +	if (needsPostProcessing) {
> >>>> +		if (processingStatus == Camera3RequestDescriptor::Status::Error) {
> >>>> +			descriptor->status_ = processingStatus;
> >>>> +			sendCaptureResults();
> >>>> +		}
> >>>> +
> >>>> +		return;
> >>>> +	}
> >>>> +
> >>>>    	descriptor->status_ = Camera3RequestDescriptor::Status::Success;
> >>>>    	sendCaptureResults();
> >>>>    }
> >>>> @@ -1206,6 +1220,64 @@ void CameraDevice::sendCaptureResults()
> >>>>    	}
> >>>>    }
> >>>>    
> >>>> +void CameraDevice::setBufferStatus(CameraStream *cameraStream,
> >>>> +				   Camera3RequestDescriptor::StreamBuffer &buffer,
> >>>> +				   Camera3RequestDescriptor *request,
> >>>> +				   Camera3RequestDescriptor::Status status)
> >>>> +{
> >>>> +	/*
> >>>> +	 * Return the FrameBuffer to the CameraStream now that we're
> >>>> +	 * done processing it.
> >>>> +	 */
> >>>> +	if (cameraStream->type() == CameraStream::Type::Internal)
> >>>> +		cameraStream->putBuffer(buffer.internalBuffer);
> >>>> +
> >>>> +	buffer.status = status;
> >>>> +	if (status != Camera3RequestDescriptor::Status::Success)
> >>>> +		notifyError(request->frameNumber_, buffer.stream->camera3Stream(),
> >>>>    +			    CAMERA3_MSG_ERROR_BUFFER);
> >>>> +}
> >>>> +
> >>>> +void CameraDevice::streamProcessingComplete(CameraStream *cameraStream,
> >>>> +					    Camera3RequestDescriptor *request,
> >>>> +					    Camera3RequestDescriptor::Status status)
> >>>> +{
> >>>> +	MutexLocker locker(request->streamsProcessMutex_);
> >>>> +	for (auto &buffer : request->buffers_) {
> >>>> +		if (buffer.stream != cameraStream)
> >>>> +			continue;
> >>>> +
> >>>> +		setBufferStatus(cameraStream, buffer, request, status);
> >>>> +	}
> >>>> +
> >>>> +	bool hasPostProcessingErrors = false;
> >>>> +	for (auto &buffer : request->buffers_) {
> >>>> +		if (cameraStream->type() == CameraStream::Type::Direct)
> >>>> +			continue;
> >>>> +
> >>>> +		/*
> >>>> +		 * Other eligible buffers might be waiting to get post-processed.
> >>>> +		 * So wait for their turn before sendCaptureResults() for the
> >>>> +		 * descriptor.
> >>>> +		 */
> >>>> +		if (buffer.status == Camera3RequestDescriptor::Status::Pending)
> >>>> +			return;
> >>>> +
> >>>> +		if (!hasPostProcessingErrors &&
> >>>> +		    buffer.status == Camera3RequestDescriptor::Status::Error)
> >>>> +			hasPostProcessingErrors = true;
> >>>> +	}
> >>>> +
> >>>> +	if (hasPostProcessingErrors)
> >>>> +		request->status_ = Camera3RequestDescriptor::Status::Error;
> >>>> +	else
> >>>> +		request->status_ = Camera3RequestDescriptor::Status::Success;
> >>>> +
> >>>> +	locker.unlock();
> >>>> +
> >>>> +	sendCaptureResults();
> >>>> +}
> >>>> +
> >>>>    std::string CameraDevice::logPrefix() const
> >>>>    {
> >>>>    	return "'" + camera_->id() + "'";
> >>>> diff --git a/src/android/camera_device.h b/src/android/camera_device.h
> >>>> index 863cf414..1ef933da 100644
> >>>> --- a/src/android/camera_device.h
> >>>> +++ b/src/android/camera_device.h
> >>>> @@ -66,6 +66,9 @@ public:
> >>>>    	int configureStreams(camera3_stream_configuration_t *stream_list);
> >>>>    	int processCaptureRequest(camera3_capture_request_t *request);
> >>>>    	void requestComplete(libcamera::Request *request);
> >>>> +	void streamProcessingComplete(CameraStream *cameraStream,
> >>>> +				      Camera3RequestDescriptor *request,
> >>>> +				      Camera3RequestDescriptor::Status status);
> >>>>    
> >>>>    protected:
> >>>>    	std::string logPrefix() const override;
> >>>> @@ -94,6 +97,10 @@ private:
> >>>>    			 camera3_error_msg_code code) const;
> >>>>    	int processControls(Camera3RequestDescriptor *descriptor);
> >>>>    	void sendCaptureResults();
> >>>> +	void setBufferStatus(CameraStream *cameraStream,
> >>>> +			     Camera3RequestDescriptor::StreamBuffer &buffer,
> >>>> +			     Camera3RequestDescriptor *request,
> >>>> +			     Camera3RequestDescriptor::Status status);
> >>>>    	std::unique_ptr<CameraMetadata> getResultMetadata(
> >>>>    		const Camera3RequestDescriptor &descriptor) const;
> >>>>    
> >>>> diff --git a/src/android/camera_request.h b/src/android/camera_request.h
> >>>> index 05dabf89..3a2774e0 100644
> >>>> --- a/src/android/camera_request.h
> >>>> +++ b/src/android/camera_request.h
> >>>> @@ -8,6 +8,7 @@
> >>>>    #define __ANDROID_CAMERA_REQUEST_H__
> >>>>    
> >>>>    #include <memory>
> >>>> +#include <mutex>
> >>>>    #include <vector>
> >>>>    
> >>>>    #include <libcamera/base/class.h>
> >>>> @@ -37,6 +38,7 @@ public:
> >>>>    		std::unique_ptr<libcamera::FrameBuffer> frameBuffer;
> >>>>    		int fence;
> >>>>    		Status status;
> >>>> +		libcamera::FrameBuffer *internalBuffer = nullptr;
> >>>>    	};
> >>>>    
> >>>>    	Camera3RequestDescriptor(libcamera::Camera *camera,
> >>>> @@ -47,6 +49,8 @@ public:
> >>>>    
> >>>>    	uint32_t frameNumber_ = 0;
> >>>>    
> >>>> +	/* Protects buffers_ for post-processing streams. */
> >>>> +	std::mutex streamsProcessMutex_;
> >>>>    	std::vector<StreamBuffer> buffers_;
> >>>>    
> >>>>    	CameraMetadata settings_;
> >>>> diff --git a/src/android/camera_stream.cpp b/src/android/camera_stream.cpp
> >>>> index f44a2717..04cbef8c 100644
> >>>> --- a/src/android/camera_stream.cpp
> >>>> +++ b/src/android/camera_stream.cpp
> >>>> @@ -22,6 +22,7 @@
> >>>>    #include "camera_capabilities.h"
> >>>>    #include "camera_device.h"
> >>>>    #include "camera_metadata.h"
> >>>> +#include "post_processor.h"
> >>>>    
> >>>>    using namespace libcamera;
> >>>>    
> >>>> @@ -97,6 +98,18 @@ int CameraStream::configure()
> >>>>    		int ret = postProcessor_->configure(configuration(), output);
> >>>>    		if (ret)
> >>>>    			return ret;
> >>>> +
> >>>> +		postProcessor_->processComplete.connect(
> >>>> +			this, [&](Camera3RequestDescriptor *request, PostProcessor::Status status) {
> >>>> +				Camera3RequestDescriptor::Status bufferStatus =
> >>>> +					Camera3RequestDescriptor::Status::Error;
> >>>> +
> >>>> +				if (status == PostProcessor::Status::Success)
> >>>> +					bufferStatus = Camera3RequestDescriptor::Status::Success;
> >>>
> >>> It looks weird to make Error a default (and thus special) case. Would
> >>> any of the following be better ?
> >>>
> >>> 				Camera3RequestDescriptor::Status bufferStatus;
> >>>
> >>> 				if (status == PostProcessor::Status::Success)
> >>> 					bufferStatus = Camera3RequestDescriptor::Status::Success;
> >>> 				else
> >>> 					bufferStatus = Camera3RequestDescriptor::Status::Error;
> >>>
> >>>
> >>> 				Camera3RequestDescriptor::Status bufferStatus =
> >>> 					status == PostProcessor::Status::Success ?
> >>> 					Camera3RequestDescriptor::Status::Success :
> >>> 					Camera3RequestDescriptor::Status::Error;
> >>>
> >>> I think I like the second option best.
> >>>
> >>>> +
> >>>> +				cameraDevice_->streamProcessingComplete(this, request,
> >>>> +									bufferStatus);
> >>>> +			});
> >>>>    	}
> >>>>    
> >>>>    	if (type_ == Type::Internal) {
> >>>> diff --git a/src/android/jpeg/post_processor_jpeg.cpp b/src/android/jpeg/post_processor_jpeg.cpp
> >>>> index 699576ef..a001fede 100644
> >>>> --- a/src/android/jpeg/post_processor_jpeg.cpp
> >>>> +++ b/src/android/jpeg/post_processor_jpeg.cpp
> >>>> @@ -198,6 +198,7 @@ int PostProcessorJpeg::process(const FrameBuffer &source,
> >>>>    					 exif.data(), quality);
> >>>>    	if (jpeg_size < 0) {
> >>>>    		LOG(JPEG, Error) << "Failed to encode stream image";
> >>>> +		processComplete.emit(request, PostProcessor::Status::Error);
> >>>
> >>> I think you can write Status::Error here and below, including in
> >>> post_processor_yuv.cpp (not above in camera_stream.cpp though).
> >>>
> >>>>    		return jpeg_size;
> >>>>    	}
> >>>>    
> >>>> @@ -211,6 +212,7 @@ int PostProcessorJpeg::process(const FrameBuffer &source,
> >>>>    
> >>>>    	/* Update the JPEG result Metadata. */
> >>>>    	resultMetadata->addEntry(ANDROID_JPEG_SIZE, jpeg_size);
> >>>> +	processComplete.emit(request, PostProcessor::Status::Success);
> >>>>    
> >>>>    	return 0;
> >>>>    }
> >>>> diff --git a/src/android/post_processor.h b/src/android/post_processor.h
> >>>> index 27eaef88..14f5e8c7 100644
> >>>> --- a/src/android/post_processor.h
> >>>> +++ b/src/android/post_processor.h
> >>>> @@ -7,6 +7,8 @@
> >>>>    #ifndef __ANDROID_POST_PROCESSOR_H__
> >>>>    #define __ANDROID_POST_PROCESSOR_H__
> >>>>    
> >>>> +#include <libcamera/base/signal.h>
> >>>> +
> >>>>    #include <libcamera/framebuffer.h>
> >>>>    #include <libcamera/stream.h>
> >>>>    
> >>>> @@ -17,6 +19,11 @@ class Camera3RequestDescriptor;
> >>>>    class PostProcessor
> >>>>    {
> >>>>    public:
> >>>> +	enum class Status {
> >>>> +		Error,
> >>>> +		Success
> >>>> +	};
> >>>> +
> >>>>    	virtual ~PostProcessor() = default;
> >>>>    
> >>>>    	virtual int configure(const libcamera::StreamConfiguration &inCfg,
> >>>> @@ -24,6 +31,8 @@ public:
> >>>>    	virtual int process(const libcamera::FrameBuffer &source,
> >>>>    			    CameraBuffer *destination,
> >>>>    			    Camera3RequestDescriptor *request) = 0;
> >>>> +
> >>>> +	libcamera::Signal<Camera3RequestDescriptor *, Status> processComplete;
> >>>>    };
> >>>>    
> >>>>    #endif /* __ANDROID_POST_PROCESSOR_H__ */
> >>>> diff --git a/src/android/yuv/post_processor_yuv.cpp b/src/android/yuv/post_processor_yuv.cpp
> >>>> index 8110a1f1..fd364741 100644
> >>>> --- a/src/android/yuv/post_processor_yuv.cpp
> >>>> +++ b/src/android/yuv/post_processor_yuv.cpp
> >>>> @@ -51,14 +51,17 @@ int PostProcessorYuv::configure(const StreamConfiguration &inCfg,
> >>>>    
> >>>>    int PostProcessorYuv::process(const FrameBuffer &source,
> >>>>    			      CameraBuffer *destination,
> >>>> -			      [[maybe_unused]] Camera3RequestDescriptor *request)
> >>>> +			      Camera3RequestDescriptor *request)
> >>>>    {
> >>>> -	if (!isValidBuffers(source, *destination))
> >>>> +	if (!isValidBuffers(source, *destination)) {
> >>>> +		processComplete.emit(request, PostProcessor::Status::Error);
> >>>>    		return -EINVAL;
> >>>> +	}
> >>>>    
> >>>>    	const MappedFrameBuffer sourceMapped(&source, MappedFrameBuffer::MapFlag::Read);
> >>>>    	if (!sourceMapped.isValid()) {
> >>>>    		LOG(YUV, Error) << "Failed to mmap camera frame buffer";
> >>>> +		processComplete.emit(request, PostProcessor::Status::Error);
> >>>>    		return -EINVAL;
> >>>>    	}
> >>>>    
> >>>> @@ -76,9 +79,12 @@ int PostProcessorYuv::process(const FrameBuffer &source,
> >>>>    				    libyuv::FilterMode::kFilterBilinear);
> >>>>    	if (ret) {
> >>>>    		LOG(YUV, Error) << "Failed NV12 scaling: " << ret;
> >>>> +		processComplete.emit(request, PostProcessor::Status::Error);
> >>>>    		return -EINVAL;
> >>>>    	}
> >>>>    
> >>>> +	processComplete.emit(request, PostProcessor::Status::Success);
> >>>> +
> >>>>    	return 0;
> >>>>    }
> >>>>