android: post_processor: Make post processing async

Introduce a dedicated worker class derived from libcamera::Thread.
The worker class maintains a queue for post-processing requests
and waits for a post-processing request to become available.
It will process them as per FIFO before de-queuing it from the
queue.

The entire post-processing handling iteration is locked under
streamsProcessMutex_ which helps us to queue all the post-processing
request at once, before any of the post-processing completion slot
(streamProcessingComplete()) is allowed to run for post-processing
requests completing in parallel. This helps us to manage both
synchronous and asynchronous errors encountered during the entire
post processing operation. Since a post-processing operation can
even complete after CameraDevice::requestComplete() has returned,
we need to check and complete the descriptor from
streamProcessingComplete() running in the PostProcessorWorker's
thread.

This patch also implements a flush() for the PostProcessorWorker
class which is responsible to purge post-processing requests
queued up while a camera is stopping/flushing. It is hooked with
CameraStream::flush(), which isn't used currently but will be
used when we handle flush/stop scenarios in greater detail
subsequently (in a different patchset).

The libcamera request completion handler CameraDevice::requestComplete()
assumes that the request that has just completed is at the front of the
queue. Now that the post-processor runs asynchronously, this isn't true
anymore, a request being post-processed will stay in the queue and a new
libcamera request may complete. Remove that assumption, and use the
request cookie to obtain the Camera3RequestDescriptor.

Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/android/camera_stream.cpp

@@ -99,6 +99,7 @@ int CameraStream::configure()
 		if (ret)
 			return ret;
 
+		worker_ = std::make_unique<PostProcessorWorker>(postProcessor_.get());
 		postProcessor_->processComplete.connect(
 			this, [&](Camera3RequestDescriptor::StreamBuffer *streamBuffer,
 				  PostProcessor::Status status) {
@@ -112,6 +113,8 @@ int CameraStream::configure()
 				cameraDevice_->streamProcessingComplete(streamBuffer,
 									bufferStatus);
 			});
+
+		worker_->start();
 	}
 
 	if (type_ == Type::Internal) {
@@ -178,10 +181,6 @@ int CameraStream::process(Camera3RequestDescriptor::StreamBuffer *streamBuffer)
 		streamBuffer->fence = -1;
 	}
 
-	/*
-	 * \todo Buffer mapping and processing should be moved to a
-	 * separate thread.
-	 */
 	const StreamConfiguration &output = configuration();
 	streamBuffer->dstBuffer = std::make_unique<CameraBuffer>(
 		*streamBuffer->camera3Buffer, output.pixelFormat, output.size,
@@ -191,11 +190,19 @@ int CameraStream::process(Camera3RequestDescriptor::StreamBuffer *streamBuffer)
 		return -EINVAL;
 	}
 
-	postProcessor_->process(streamBuffer);
+	worker_->queueRequest(streamBuffer);
 
 	return 0;
 }
 
+void CameraStream::flush()
+{
+	if (!postProcessor_)
+		return;
+
+	worker_->flush();
+}
+
 FrameBuffer *CameraStream::getBuffer()
 {
 	if (!allocator_)
@@ -223,3 +230,87 @@ void CameraStream::putBuffer(FrameBuffer *buffer)
 
 	buffers_.push_back(buffer);
 }
+
+CameraStream::PostProcessorWorker::PostProcessorWorker(PostProcessor *postProcessor)
+	: postProcessor_(postProcessor)
+{
+}
+
+CameraStream::PostProcessorWorker::~PostProcessorWorker()
+{
+	{
+		libcamera::MutexLocker lock(mutex_);
+		state_ = State::Stopped;
+	}
+
+	cv_.notify_one();
+	wait();
+}
+
+void CameraStream::PostProcessorWorker::start()
+{
+	{
+		libcamera::MutexLocker lock(mutex_);
+		ASSERT(state_ != State::Running);
+		state_ = State::Running;
+	}
+
+	Thread::start();
+}
+
+void CameraStream::PostProcessorWorker::queueRequest(Camera3RequestDescriptor::StreamBuffer *dest)
+{
+	{
+		MutexLocker lock(mutex_);
+		ASSERT(state_ == State::Running);
+		requests_.push(dest);
+	}
+
+	cv_.notify_one();
+}
+
+void CameraStream::PostProcessorWorker::run()
+{
+	MutexLocker locker(mutex_);
+
+	while (1) {
+		cv_.wait(locker, [&] {
+			return state_ != State::Running || !requests_.empty();
+		});
+
+		if (state_ != State::Running)
+			break;
+
+		Camera3RequestDescriptor::StreamBuffer *streamBuffer = requests_.front();
+		requests_.pop();
+		locker.unlock();
+
+		postProcessor_->process(streamBuffer);
+
+		locker.lock();
+	}
+
+	if (state_ == State::Flushing) {
+		std::queue<Camera3RequestDescriptor::StreamBuffer *> requests =
+			std::move(requests_);
+		locker.unlock();
+
+		while (!requests.empty()) {
+			postProcessor_->processComplete.emit(
+				requests.front(), PostProcessor::Status::Error);
+			requests.pop();
+		}
+
+		locker.lock();
+		state_ = State::Stopped;
+	}
+}
+
+void CameraStream::PostProcessorWorker::flush()
+{
+	libcamera::MutexLocker lock(mutex_);
+	state_ = State::Flushing;
+	lock.unlock();
+
+	cv_.notify_one();
+}