Requeue unacknowledged entity updates rather than resend then "as is".

Often, by the time the UDPServer realizes that an entity update packet
has not been acknowledged, there is a newer update for the same entity
already queued up or there is a higher priority update that should be
sent first. This patch eliminates 1:1 packet resends for unacked entity
update packets. Insteawd, unacked update packets are decomposed into the
original entity updates and those updates are placed back into the
priority queues based on their new priority but the original update
timestamp. This will generally place them at the head of the line to be
put back on the wire as a new outgoing packet but prevents the resend
queue from filling up with multiple stale updates for the same entity.
This new approach takes advantage of the UDP nature of the Linden protocol
in that the intent of a reliable update packet is that if it goes
unacknowledge, SOMETHING has to happen to get the update to the client.
We are simply making sure that we are resending current object state
rather than stale object state.

Additionally, this patch includes a generalized callback mechanism so
that any caller can specify their own method to call when a packet
expires without being acknowledged. We use this mechanism to requeue
update packets and otherwise use the UDPServer default method of just
putting expired packets in the resend queue.

1 files changed, 17 insertions, 0 deletions

diff --git a/OpenSim/Framework/Util.cs b/OpenSim/Framework/Util.cs
index 5a5046e..aaa2724 100644
--- a/OpenSim/Framework/Util.cs
+++ b/OpenSim/Framework/Util.cs
@@ -1537,6 +1537,23 @@ namespace OpenSim.Framework
             return (diff >= 0) ? diff : (diff + EnvironmentTickCountMask + 1);
         }
 
+        // Returns value of Tick Count A - TickCount B accounting for wrapping of TickCount
+        // Assumes both tcA and tcB came from previous calls to Util.EnvironmentTickCount().
+        // A positive return value indicates A occured later than B
+        public static Int32 EnvironmentTickCountCompare(Int32 tcA, Int32 tcB)
+        {
+            // A, B and TC are all between 0 and 0x3fffffff
+            int tc = EnvironmentTickCount();
+
+            if (tc - tcA >= 0)
+                tcA += EnvironmentTickCountMask + 1;
+
+            if (tc - tcB >= 0)
+                tcB += EnvironmentTickCountMask + 1;
+
+            return tcA - tcB;
+        }
+
         /// <summary>
         /// Prints the call stack at any given point. Useful for debugging.
         /// </summary>