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, 32 insertions, 32 deletions

diff --git a/OpenSim/Region/ClientStack/LindenUDP/LLUDPServer.cs b/OpenSim/Region/ClientStack/LindenUDP/LLUDPServer.cs
index d08b25f..0848979 100644
--- a/OpenSim/Region/ClientStack/LindenUDP/LLUDPServer.cs
+++ b/OpenSim/Region/ClientStack/LindenUDP/LLUDPServer.cs
@@ -297,7 +297,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                         delegate(IClientAPI client)
                         {
                             if (client is LLClientView)
-                                SendPacketData(((LLClientView)client).UDPClient, data, packet.Type, category);
+                                SendPacketData(((LLClientView)client).UDPClient, data, packet.Type, category, null);
                         }
                     );
                 }
@@ -309,7 +309,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                     delegate(IClientAPI client)
                     {
                         if (client is LLClientView)
-                            SendPacketData(((LLClientView)client).UDPClient, data, packet.Type, category);
+                            SendPacketData(((LLClientView)client).UDPClient, data, packet.Type, category, null);
                     }
                 );
             }
@@ -322,7 +322,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
         /// <param name="packet"></param>
         /// <param name="category"></param>
         /// <param name="allowSplitting"></param>
-        public void SendPacket(LLUDPClient udpClient, Packet packet, ThrottleOutPacketType category, bool allowSplitting)
+        public void SendPacket(LLUDPClient udpClient, Packet packet, ThrottleOutPacketType category, bool allowSplitting, UnackedPacketMethod method)
         {
             // CoarseLocationUpdate packets cannot be split in an automated way
             if (packet.Type == PacketType.CoarseLocationUpdate && allowSplitting)
@@ -339,13 +339,13 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                 for (int i = 0; i < packetCount; i++)
                 {
                     byte[] data = datas[i];
-                    SendPacketData(udpClient, data, packet.Type, category);
+                    SendPacketData(udpClient, data, packet.Type, category, method);
                 }
             }
             else
             {
                 byte[] data = packet.ToBytes();
-                SendPacketData(udpClient, data, packet.Type, category);
+                SendPacketData(udpClient, data, packet.Type, category, method);
             }
         }
 
@@ -356,7 +356,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
         /// <param name="data"></param>
         /// <param name="type"></param>
         /// <param name="category"></param>        
-        public void SendPacketData(LLUDPClient udpClient, byte[] data, PacketType type, ThrottleOutPacketType category)
+        public void SendPacketData(LLUDPClient udpClient, byte[] data, PacketType type, ThrottleOutPacketType category, UnackedPacketMethod method)
         {
             int dataLength = data.Length;
             bool doZerocode = (data[0] & Helpers.MSG_ZEROCODED) != 0;
@@ -411,7 +411,9 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 
             #region Queue or Send
 
-            OutgoingPacket outgoingPacket = new OutgoingPacket(udpClient, buffer, category);
+            OutgoingPacket outgoingPacket = new OutgoingPacket(udpClient, buffer, category, null);
+            // If we were not provided a method for handling unacked, use the UDPServer default method
+            outgoingPacket.UnackedMethod = ((method == null) ? delegate() { ResendUnacked(outgoingPacket); } : method);
 
             // If a Linden Lab 1.23.5 client receives an update packet after a kill packet for an object, it will 
             // continue to display the deleted object until relog.  Therefore, we need to always queue a kill object
@@ -445,7 +447,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                 packet.Header.Reliable = false;
                 packet.Packets = blocks.ToArray();
 
-                SendPacket(udpClient, packet, ThrottleOutPacketType.Unknown, true);
+                SendPacket(udpClient, packet, ThrottleOutPacketType.Unknown, true, null);
             }
         }
 
@@ -458,17 +460,17 @@ namespace OpenSim.Region.ClientStack.LindenUDP
             // We *could* get OldestUnacked, but it would hurt performance and not provide any benefit
             pc.PingID.OldestUnacked = 0;
 
-            SendPacket(udpClient, pc, ThrottleOutPacketType.Unknown, false);
+            SendPacket(udpClient, pc, ThrottleOutPacketType.Unknown, false, null);
         }
 
         public void CompletePing(LLUDPClient udpClient, byte pingID)
         {
             CompletePingCheckPacket completePing = new CompletePingCheckPacket();
             completePing.PingID.PingID = pingID;
-            SendPacket(udpClient, completePing, ThrottleOutPacketType.Unknown, false);
+            SendPacket(udpClient, completePing, ThrottleOutPacketType.Unknown, false, null);
         }
 
-        public void ResendUnacked(LLUDPClient udpClient)
+        public void HandleUnacked(LLUDPClient udpClient)
         {
             if (!udpClient.IsConnected)
                 return;
@@ -488,31 +490,29 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 
             if (expiredPackets != null)
             {
-                //m_log.Debug("[LLUDPSERVER]: Resending " + expiredPackets.Count + " packets to " + udpClient.AgentID + ", RTO=" + udpClient.RTO);
-
+                //m_log.Debug("[LLUDPSERVER]: Handling " + expiredPackets.Count + " packets to " + udpClient.AgentID + ", RTO=" + udpClient.RTO);
                 // Exponential backoff of the retransmission timeout
                 udpClient.BackoffRTO();
+                for (int i = 0; i < expiredPackets.Count; ++i)
+                    expiredPackets[i].UnackedMethod();
+            }
+        }
 
-                // Resend packets
-                for (int i = 0; i < expiredPackets.Count; i++)
-                {
-                    OutgoingPacket outgoingPacket = expiredPackets[i];
-
-                    //m_log.DebugFormat("[LLUDPSERVER]: Resending packet #{0} (attempt {1}), {2}ms have passed",
-                    //    outgoingPacket.SequenceNumber, outgoingPacket.ResendCount, Environment.TickCount - outgoingPacket.TickCount);
+        public void ResendUnacked(OutgoingPacket outgoingPacket)
+        {
+            //m_log.DebugFormat("[LLUDPSERVER]: Resending packet #{0} (attempt {1}), {2}ms have passed",
+            //    outgoingPacket.SequenceNumber, outgoingPacket.ResendCount, Environment.TickCount - outgoingPacket.TickCount);
 
-                    // Set the resent flag
-                    outgoingPacket.Buffer.Data[0] = (byte)(outgoingPacket.Buffer.Data[0] | Helpers.MSG_RESENT);
-                    outgoingPacket.Category = ThrottleOutPacketType.Resend;
+            // Set the resent flag
+            outgoingPacket.Buffer.Data[0] = (byte)(outgoingPacket.Buffer.Data[0] | Helpers.MSG_RESENT);
+            outgoingPacket.Category = ThrottleOutPacketType.Resend;
 
-                    // Bump up the resend count on this packet
-                    Interlocked.Increment(ref outgoingPacket.ResendCount);
+            // Bump up the resend count on this packet
+            Interlocked.Increment(ref outgoingPacket.ResendCount);
 
-                    // Requeue or resend the packet
-                    if (!outgoingPacket.Client.EnqueueOutgoing(outgoingPacket, false))
-                        SendPacketFinal(outgoingPacket);
-                }
-            }
+            // Requeue or resend the packet
+            if (!outgoingPacket.Client.EnqueueOutgoing(outgoingPacket, false))
+                SendPacketFinal(outgoingPacket);
         }
 
         public void Flush(LLUDPClient udpClient)
@@ -1096,7 +1096,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                     if (udpClient.IsConnected)
                     {
                         if (m_resendUnacked)
-                            ResendUnacked(udpClient);
+                            HandleUnacked(udpClient);
 
                         if (m_sendAcks)
                             SendAcks(udpClient);
@@ -1152,7 +1152,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                             nticksUnack++;
                             watch2.Start();
 
-                            ResendUnacked(udpClient);
+                            HandleUnacked(udpClient);
 
                             watch2.Stop();
                             avgResendUnackedTicks = (nticksUnack - 1)/(float)nticksUnack * avgResendUnackedTicks + (watch2.ElapsedTicks / (float)nticksUnack);