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.

OpenSim/Framework/IClientAPI.cs

@@ -572,34 +572,69 @@ namespace OpenSim.Framework
 
     public class IEntityUpdate
     {
-        public ISceneEntity Entity;
+        private ISceneEntity m_entity;
-        public uint Flags;
+        private uint m_flags;
+        private int m_updateTime;
+
+        public ISceneEntity Entity
+        {
+            get { return m_entity; }
+        }
+
+        public uint Flags
+        {
+            get { return m_flags; }
+        }
+
+        public int UpdateTime
+        {
+            get { return m_updateTime; }
+        }
 
         public virtual void Update(IEntityUpdate update)
         {
-            this.Flags |= update.Flags;
+            m_flags |= update.Flags;
+
+            // Use the older of the updates as the updateTime
+            if (Util.EnvironmentTickCountCompare(UpdateTime, update.UpdateTime) > 0)
+                m_updateTime = update.UpdateTime;
         }
 
         public IEntityUpdate(ISceneEntity entity, uint flags)
         {
-            Entity = entity;
+            m_entity = entity;
-            Flags = flags;
+            m_flags = flags;
-        }
+            m_updateTime = Util.EnvironmentTickCount();
         }
 
+        public IEntityUpdate(ISceneEntity entity, uint flags, Int32 updateTime)
+        {
+            m_entity = entity;
+            m_flags = flags;
+            m_updateTime = updateTime;
+        }
+    }
 
     public class EntityUpdate : IEntityUpdate
     {
-        // public ISceneEntity Entity;
+        private float m_timeDilation;
-        // public PrimUpdateFlags Flags;
+
-        public float TimeDilation;
+        public float TimeDilation
+        {
+            get { return m_timeDilation; }
+        }
 
         public EntityUpdate(ISceneEntity entity, PrimUpdateFlags flags, float timedilation)
-            : base(entity,(uint)flags)
+            : base(entity, (uint)flags)
         {
-            //Entity = entity;
             // Flags = flags;
-            TimeDilation = timedilation;
+            m_timeDilation = timedilation;
+        }
+
+        public EntityUpdate(ISceneEntity entity, PrimUpdateFlags flags, float timedilation, Int32 updateTime)
+            : base(entity,(uint)flags,updateTime)
+        {
+            m_timeDilation = timedilation;
         }
     }
 

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>

OpenSim/Region/ClientStack/LindenUDP/LLClientView.cs

@@ -3561,6 +3561,34 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                 m_entityUpdates.Enqueue(priority, new EntityUpdate(entity, updateFlags, m_scene.TimeDilation));
         }
 
+        /// <summary>
+        /// Requeue an EntityUpdate when it was not acknowledged by the client. 
+        /// We will update the priority and put it in the correct queue, merging update flags 
+        /// with any other updates that may be queued for the same entity. 
+        /// The original update time is used for the merged update.
+        /// </summary>
+        public void ResendPrimUpdate(EntityUpdate update)
+        {
+            // If the update exists in priority queue, it will be updated.
+            // If it does not exist then it will be added with the current (rather than its original) priority
+            uint priority = m_prioritizer.GetUpdatePriority(this, update.Entity);
+
+            lock (m_entityUpdates.SyncRoot)
+                m_entityUpdates.Enqueue(priority, update);
+        }
+
+        /// <summary>
+        /// Requeue a list of EntityUpdates when they were not acknowledged by the client. 
+        /// We will update the priority and put it in the correct queue, merging update flags 
+        /// with any other updates that may be queued for the same entity. 
+        /// The original update time is used for the merged update.
+        /// </summary>
+        void ResendPrimUpdates(List<EntityUpdate> updates)
+        {
+            foreach (EntityUpdate update in updates)
+                ResendPrimUpdate(update);
+        }
+
         private void ProcessEntityUpdates(int maxUpdates)
         {
             OpenSim.Framework.Lazy<List<ObjectUpdatePacket.ObjectDataBlock>> objectUpdateBlocks = new OpenSim.Framework.Lazy<List<ObjectUpdatePacket.ObjectDataBlock>>();
@@ -3568,6 +3596,11 @@ namespace OpenSim.Region.ClientStack.LindenUDP
             OpenSim.Framework.Lazy<List<ImprovedTerseObjectUpdatePacket.ObjectDataBlock>> terseUpdateBlocks = new OpenSim.Framework.Lazy<List<ImprovedTerseObjectUpdatePacket.ObjectDataBlock>>();
             OpenSim.Framework.Lazy<List<ImprovedTerseObjectUpdatePacket.ObjectDataBlock>> terseAgentUpdateBlocks = new OpenSim.Framework.Lazy<List<ImprovedTerseObjectUpdatePacket.ObjectDataBlock>>();
 
+            OpenSim.Framework.Lazy<List<EntityUpdate>> objectUpdates = new OpenSim.Framework.Lazy<List<EntityUpdate>>();
+            OpenSim.Framework.Lazy<List<EntityUpdate>> compressedUpdates = new OpenSim.Framework.Lazy<List<EntityUpdate>>();
+            OpenSim.Framework.Lazy<List<EntityUpdate>> terseUpdates = new OpenSim.Framework.Lazy<List<EntityUpdate>>();
+            OpenSim.Framework.Lazy<List<EntityUpdate>> terseAgentUpdates = new OpenSim.Framework.Lazy<List<EntityUpdate>>();
+
             // Check to see if this is a flush
             if (maxUpdates <= 0)
             {
@@ -3688,24 +3721,33 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                         if (update.Entity is ScenePresence)
                         {
                             objectUpdateBlocks.Value.Add(CreateAvatarUpdateBlock((ScenePresence)update.Entity));
+                            objectUpdates.Value.Add(update);
                         }
                         else
                         {
                             objectUpdateBlocks.Value.Add(CreatePrimUpdateBlock((SceneObjectPart)update.Entity, this.m_agentId));
+                            objectUpdates.Value.Add(update);
                         }
                     }
                     else if (!canUseImproved)
                     {
                         compressedUpdateBlocks.Value.Add(CreateCompressedUpdateBlock((SceneObjectPart)update.Entity, updateFlags));
+                        compressedUpdates.Value.Add(update);
                     }
                     else
                     {
                         if (update.Entity is ScenePresence && ((ScenePresence)update.Entity).UUID == AgentId)
+                        {
                             // Self updates go into a special list
                             terseAgentUpdateBlocks.Value.Add(CreateImprovedTerseBlock(update.Entity, updateFlags.HasFlag(PrimUpdateFlags.Textures)));
+                            terseAgentUpdates.Value.Add(update);
+                        }
                         else
+                        {
                             // Everything else goes here
                             terseUpdateBlocks.Value.Add(CreateImprovedTerseBlock(update.Entity, updateFlags.HasFlag(PrimUpdateFlags.Textures)));
+                            terseUpdates.Value.Add(update);
+                        }
                     }
     
                     #endregion Block Construction
@@ -3713,10 +3755,6 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                 
     
                 #region Packet Sending
-        
-                //const float TIME_DILATION = 1.0f;
-
-
                 ushort timeDilation = Utils.FloatToUInt16(avgTimeDilation, 0.0f, 1.0f);
 
                 if (terseAgentUpdateBlocks.IsValueCreated)
@@ -3730,9 +3768,8 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 
                     for (int i = 0; i < blocks.Count; i++)
                         packet.ObjectData[i] = blocks[i];
-
+                    // If any of the packets created from this call go unacknowledged, all of the updates will be resent
-                    
+                    OutPacket(packet, ThrottleOutPacketType.Unknown, true, delegate() { ResendPrimUpdates(terseAgentUpdates.Value); });
-                    OutPacket(packet, ThrottleOutPacketType.Unknown, true);
                 }
 
                 if (objectUpdateBlocks.IsValueCreated)
@@ -3746,8 +3783,8 @@ namespace OpenSim.Region.ClientStack.LindenUDP
         
                     for (int i = 0; i < blocks.Count; i++)
                         packet.ObjectData[i] = blocks[i];
-        
+                    // If any of the packets created from this call go unacknowledged, all of the updates will be resent
-                    OutPacket(packet, ThrottleOutPacketType.Task, true);
+                    OutPacket(packet, ThrottleOutPacketType.Task, true, delegate() { ResendPrimUpdates(objectUpdates.Value); });
                 }
         
                 if (compressedUpdateBlocks.IsValueCreated)
@@ -3761,8 +3798,8 @@ namespace OpenSim.Region.ClientStack.LindenUDP
         
                     for (int i = 0; i < blocks.Count; i++)
                         packet.ObjectData[i] = blocks[i];
-        
+                    // If any of the packets created from this call go unacknowledged, all of the updates will be resent
-                    OutPacket(packet, ThrottleOutPacketType.Task, true);
+                    OutPacket(packet, ThrottleOutPacketType.Task, true, delegate() { ResendPrimUpdates(compressedUpdates.Value); });
                 }
 
                 if (terseUpdateBlocks.IsValueCreated)
@@ -3776,8 +3813,8 @@ namespace OpenSim.Region.ClientStack.LindenUDP
         
                     for (int i = 0; i < blocks.Count; i++)
                         packet.ObjectData[i] = blocks[i];
-        
+                    // If any of the packets created from this call go unacknowledged, all of the updates will be resent
-                    OutPacket(packet, ThrottleOutPacketType.Task, true);
+                    OutPacket(packet, ThrottleOutPacketType.Task, true, delegate() { ResendPrimUpdates(terseUpdates.Value); });
                 }
             }
 
@@ -3969,7 +4006,8 @@ namespace OpenSim.Region.ClientStack.LindenUDP
             {
                 SendFamilyProps = SendFamilyProps || update.SendFamilyProps;
                 SendObjectProps = SendObjectProps || update.SendObjectProps;
-                Flags |= update.Flags;
+                // other properties may need to be updated by base class
+                base.Update(update);
             }
         }
         
@@ -11362,6 +11400,22 @@ namespace OpenSim.Region.ClientStack.LindenUDP
         /// packets (the default), or false to disable splitting if the calling code
         /// handles splitting manually</param>
         protected void OutPacket(Packet packet, ThrottleOutPacketType throttlePacketType, bool doAutomaticSplitting)
+        {
+            OutPacket(packet, throttlePacketType, doAutomaticSplitting, null);
+        }
+
+        /// <summary>
+        /// This is the starting point for sending a simulator packet out to the client
+        /// </summary>
+        /// <param name="packet">Packet to send</param>
+        /// <param name="throttlePacketType">Throttling category for the packet</param>
+        /// <param name="doAutomaticSplitting">True to automatically split oversized
+        /// packets (the default), or false to disable splitting if the calling code
+        /// handles splitting manually</param>
+        /// <param name="method">The method to be called in the event this packet is reliable
+        /// and unacknowledged. The server will provide normal resend capability if you do not
+        /// provide your own method.</param>
+        protected void OutPacket(Packet packet, ThrottleOutPacketType throttlePacketType, bool doAutomaticSplitting, UnackedPacketMethod method)
         {
             if (m_debugPacketLevel > 0)
             {
@@ -11388,7 +11442,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                     m_log.DebugFormat("[CLIENT]: Packet OUT {0}", packet.Type);
             }
             
-            m_udpServer.SendPacket(m_udpClient, packet, throttlePacketType, doAutomaticSplitting);
+            m_udpServer.SendPacket(m_udpClient, packet, throttlePacketType, doAutomaticSplitting, method);
         }
 
         public bool AddMoney(int debit)

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;
@@ -488,16 +490,16 @@ 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
+        public void ResendUnacked(OutgoingPacket outgoingPacket)
-                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);
 
@@ -512,8 +514,6 @@ namespace OpenSim.Region.ClientStack.LindenUDP
             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);

OpenSim/Region/ClientStack/LindenUDP/OutgoingPacket.cs

@@ -31,6 +31,7 @@ using OpenMetaverse;
 
 namespace OpenSim.Region.ClientStack.LindenUDP
 {
+    public delegate void UnackedPacketMethod();
     /// <summary>
     /// Holds a reference to the <seealso cref="LLUDPClient"/> this packet is
     /// destined for, along with the serialized packet data, sequence number
@@ -52,6 +53,8 @@ namespace OpenSim.Region.ClientStack.LindenUDP
         public int TickCount;
         /// <summary>Category this packet belongs to</summary>
         public ThrottleOutPacketType Category;
+        /// <summary>The delegate to be called if this packet is determined to be unacknowledged</summary>
+        public UnackedPacketMethod UnackedMethod;
 
         /// <summary>
         /// Default constructor
@@ -60,11 +63,12 @@ namespace OpenSim.Region.ClientStack.LindenUDP
         /// <param name="buffer">Serialized packet data. If the flags or sequence number
         /// need to be updated, they will be injected directly into this binary buffer</param>
         /// <param name="category">Throttling category for this packet</param>
-        public OutgoingPacket(LLUDPClient client, UDPPacketBuffer buffer, ThrottleOutPacketType category)
+        public OutgoingPacket(LLUDPClient client, UDPPacketBuffer buffer, ThrottleOutPacketType category, UnackedPacketMethod method)
         {
             Client = client;
             Buffer = buffer;
             Category = category;
+            UnackedMethod = method;
         }
     }
 }