BMediaEventLooper: Use enqueue_time in a different shape

* This is the only solution that allowed to use the best
of both ways to do this calculus. I've also tested it
with a modified sound player that snoozed every time
the buffer should be handled, and found that neither
of the lateness calculus I tested (including enqueue_time)
really solve all problems. That's why I've tried to find
an average solution. There's still room for improvements
eventually.

headers/os/media/TimedEventQueue.h

@@ -38,8 +38,9 @@ struct media_timed_event {
 			int32				data;
 			int64				bigdata;
 			char				user_data[64];
+			bigtime_t			enqueue_time;
 
-			uint32				_reserved_media_timed_event_[8];
+			uint32				_reserved_media_timed_event_[6];
 };
 
 

src/kits/media/MediaEventLooper.cpp

@@ -242,11 +242,24 @@ BMediaEventLooper::ControlLoop()
 				err = fRealTimeQueue.RemoveFirstEvent(&event);
 
 			if (err == B_OK) {
-				// We are going to do this calculus in real time
-				// because otherwise we could get erroneous values.
-				// This calculus allow us to detect both early and late
-				// buffers, this is the meaning of the lateness concept.
-				bigtime_t lateness = waitUntil - TimeSource()->RealTime();
+				// The general idea of lateness is to allow
+				// the client code to detect when the buffer
+				// is handled late or early. What we add is
+				// that the code log the time at which the
+				// current event is added to the queue. This
+				// allow us to detect cyclic/stagnant latency
+				// in the meantime, so that the client can
+				// notify to the producer only the portion
+				// that might be attributable.
+				bigtime_t lateness = 0;
+				if (waitUntil > 0) {
+					lateness = waitUntil - TimeSource()->RealTime();
+					if (lateness > 0) {
+						bigtime_t enqueueLatency = event.enqueue_time - waitUntil;
+						if (enqueueLatency > 0)
+							lateness += enqueueLatency;
+					}
+				}
 				DispatchEvent(&event, -lateness, hasRealtime);
 			}
 		} else if (err != B_OK)

src/kits/media/TimedEventQueuePrivate.cpp

@@ -78,6 +78,9 @@ _event_queue_imp::AddEvent(const media_timed_event &event)
 		 return B_BAD_VALUE;
 	}
 
+	const_cast<media_timed_event&>(event).enqueue_time =
+		BTimeSource::RealTime();
+
 	//create a new queue
 	if (fFirstEntry == NULL) {
 		ASSERT(fEventCount == 0);