libcamera: camera: Assert pipelines complete all requests

When the camera manager calls stop on a pipeline, it is expected that
the pipeline handler guarantees all requests are returned back to the
application before the camera has stopped.

Ensure that this guarantee is met by providing an accessor on the
pipeline handler to validate that all pending requests are removed.

Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/internal/pipeline_handler.h

@@ -80,6 +80,7 @@ public:
 
 	virtual int start(Camera *camera, const ControlList *controls) = 0;
 	virtual void stop(Camera *camera) = 0;
+	bool hasPendingRequests(const Camera *camera) const;
 
 	void queueRequest(Request *request);
 

src/libcamera/camera.cpp

@@ -1084,6 +1084,8 @@ int Camera::stop()
 	d->pipe_->invokeMethod(&PipelineHandler::stop, ConnectionTypeBlocking,
 			       this);
 
+	ASSERT(!d->pipe_->hasPendingRequests(this));
+
 	d->setState(Private::CameraConfigured);
 
 	return 0;

src/libcamera/pipeline_handler.cpp

@@ -368,6 +368,21 @@ const ControlList &PipelineHandler::properties(const Camera *camera) const
  * \context This function is called from the CameraManager thread.
  */
 
+/**
+ * \brief Determine if the camera has any requests pending
+ * \param[in] camera The camera to check
+ *
+ * This method determines if there are any requests queued to the pipeline
+ * awaiting processing.
+ *
+ * \return True if there are pending requests, or false otherwise
+ */
+bool PipelineHandler::hasPendingRequests(const Camera *camera) const
+{
+	const CameraData *data = cameraData(camera);
+	return !data->queuedRequests_.empty();
+}
+
 /**
  * \fn PipelineHandler::queueRequest()
  * \brief Queue a request