IoUringAssmEngn: add assembleFrameReq

Invoke it instimFrameProductionTimesliceInd.

Also, we discovered:
* stream_descriptor::release() doesn't fully release all metadata
  from the fd it was assigned. This suggests that we should go
  through the codebase and do: release()=>reset() whenever we
  wish to release().
* We've confirmed that spinlocks can be used to prevent race
  conditions between stop() and handler methods.

stimBuffApis/livoxGen1/ioUringAssemblyEngine.h

@@ -14,6 +14,10 @@
 #include <boost/asio/deadline_timer.hpp>
 #include <boost/asio/posix/stream_descriptor.hpp>
 #include <livoxProto1/device.h>
+#include <asynchronousContinuation.h>
+#include <asynchronousLoop.h>
+#include <callback.h>
+#include <spinLock.h>
 #include "frameAssemblyDesc.h"
 
 namespace smo {
@@ -29,9 +33,13 @@ public:
 
 	bool setup();
 	void finalize();
-	void resetAndAssembleFrame(
-		std::function<void(void*)> onCqeReady);
-	void stop();
+
+	typedef std::function<void(void*, int)> resetAndAssembleFrameCbFn;
+	void resetAndAssembleFrame(resetAndAssembleFrameCbFn onCqeReady);
+	void stop(bool doAcquireLock = true);
+
+	typedef std::function<void(bool, AsynchronousLoop)> assembleFrameReqCbFn;
+	void assembleFrameReq(Callback<assembleFrameReqCbFn> cb);
 
 	// Telemetry helpers
 	static size_t computePointsPerDgram(int returnMode);
@@ -57,12 +65,19 @@ private:
 
 	// Stall detection timer
 	boost::asio::deadline_timer stallTimer;
-	// Callback for CQE notifications (called with user_data from each CQE)
-	std::function<void(void*)> onCqeReadyCallback;
+	// Callback for CQE ntfns (called with user_data+result from each CQE)
+	resetAndAssembleFrameCbFn onCqeReadyCallback;
+	// Flag to indicate assembly is in progress (cleared by stop())
+	// Protected by isAssemblingLock
+	SpinLock isAssemblingLock;
+	bool isAssembling;
 
 	void cancelIncompleteAndFillDummies();
 	void onEventfdRead(
 		const boost::system::error_code& error, std::size_t bytes_transferred);
+
+	class AssembleFrameReq;
+	friend class AssembleFrameReq;
 };
 
 } // namespace stim_buff