StimulusBuffer should take ref to parent; not sh_ptr to common instance

include/user/stimulusBuffer.h

@@ -18,18 +18,18 @@ class StimulusProducer;
  * StimulusBuffer manages a collection of stimulus frames and ring buffer.
  *
  * This buffer holds the actual frame storage and ring buffer for stimulus
- * data. It maintains a reference to the StimulusProducer that it owns.
+ * data. It maintains a reference to its parent StimulusProducer.
  */
 class StimulusBuffer
 {
 public:
 	explicit StimulusBuffer(
-		std::shared_ptr<StimulusProducer> &producer,
+		StimulusProducer& parent,
 		const std::shared_ptr<device::DeviceAttachmentSpec>
 			&deviceAttachmentSpec,
 		int histbuffMs,
 		const SpMcRingBuffer::InputEngineConstraints& ringBufferConstraints)
-	: producer(producer),
+	: parent(parent),
 	deviceAttachmentSpec(deviceAttachmentSpec),
 	histbuffMs(histbuffMs),
 	frames_(static_cast<size_t>(histbuffMs / CONFIG_STIMBUFF_FRAME_PERIOD_MS)),
@@ -48,7 +48,7 @@ public:
 	StimulusBuffer& operator=(StimulusBuffer&&) = default;
 
 public:
-	std::shared_ptr<StimulusProducer> producer;
+	StimulusProducer& parent;
 	std::shared_ptr<device::DeviceAttachmentSpec> deviceAttachmentSpec;
 	int histbuffMs;
 	std::vector<StimulusFrame> frames_;