cam: Move request processing to main thread

The request completion handler is invoked in the camera manager thread,
which shouldn't be blocked for large amounts of time. As writing the
frames to disk can be a time-consuming process, move request processing
to the main thread by queueing an event to the event loop.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/cam/capture.cpp

@@ -157,6 +157,15 @@ void Capture::requestComplete(Request *request)
 	if (request->status() == Request::RequestCancelled)
 		return;
 
+	/*
+	 * Defer processing of the completed request to the event loop, to avoid
+	 * blocking the camera manager thread.
+	 */
+	loop_->callLater([=]() { processRequest(request); });
+}
+
+void Capture::processRequest(Request *request)
+{
 	const Request::BufferMap &buffers = request->buffers();
 
 	/*

src/cam/capture.h

@@ -33,6 +33,7 @@ private:
 	int capture(libcamera::FrameBufferAllocator *allocator);
 
 	void requestComplete(libcamera::Request *request);
+	void processRequest(libcamera::Request *request);
 
 	std::shared_ptr<libcamera::Camera> camera_;
 	libcamera::CameraConfiguration *config_;