* Handle UseCircuitCode packets asynchronously. Adding an agent to a scene can take several seconds, and was blocking up packet handling in the meantime

* Clamp retransmission timeout values between three and 10 seconds
* Log outgoing time for a packet right after it is sent instead of well before
* Loop through the entire UnackedPacketCollection when looking for expired packets

OpenSim/Region/ClientStack/LindenUDP/LLUDPClient.cs

@@ -505,8 +505,11 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                 SRTT = (1.0f - ALPHA) * SRTT + ALPHA * r;
             }
 
-            // Always round retransmission timeout up to two seconds
+            RTO = (int)(SRTT + Math.Max(m_udpServer.TickCountResolution, K * RTTVAR));
-            RTO = Math.Max(2000, (int)(SRTT + Math.Max(m_udpServer.TickCountResolution, K * RTTVAR)));
+
+            // Clamp the retransmission timeout to manageable values
+            RTO = Utils.Clamp(RTO, 3000, 10000);
+
             //m_log.Debug("[LLUDPCLIENT]: Setting agent " + this.Agent.FullName + "'s RTO to " + RTO + "ms with an RTTVAR of " +
             //    RTTVAR + " based on new RTT of " + r + "ms");
         }

OpenSim/Region/ClientStack/LindenUDP/LLUDPServer.cs

@@ -381,7 +381,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 
             // Disconnect an agent if no packets are received for some time
             //FIXME: Make 60 an .ini setting
-            if (Environment.TickCount - udpClient.TickLastPacketReceived > 1000 * 60)
+            if ((Environment.TickCount & Int32.MaxValue) - udpClient.TickLastPacketReceived > 1000 * 60)
             {
                 m_log.Warn("[LLUDPSERVER]: Ack timeout, disconnecting " + udpClient.AgentID);
 
@@ -439,9 +439,6 @@ namespace OpenSim.Region.ClientStack.LindenUDP
             if (!udpClient.IsConnected)
                 return;
 
-            // Keep track of when this packet was sent out (right now)
-            outgoingPacket.TickCount = Environment.TickCount;
-
             #region ACK Appending
 
             int dataLength = buffer.DataLength;
@@ -494,6 +491,9 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 
             // Put the UDP payload on the wire
             AsyncBeginSend(buffer);
+
+            // Keep track of when this packet was sent out (right now)
+            outgoingPacket.TickCount = Environment.TickCount & Int32.MaxValue;
         }
 
         protected override void PacketReceived(UDPPacketBuffer buffer)
@@ -536,7 +536,19 @@ namespace OpenSim.Region.ClientStack.LindenUDP
             // UseCircuitCode handling
             if (packet.Type == PacketType.UseCircuitCode)
             {
-                AddNewClient((UseCircuitCodePacket)packet, (IPEndPoint)buffer.RemoteEndPoint);
+                Util.FireAndForget(
+                    delegate(object o)
+                    {
+                        IPEndPoint remoteEndPoint = (IPEndPoint)buffer.RemoteEndPoint;
+
+                        // Begin the process of adding the client to the simulator
+                        AddNewClient((UseCircuitCodePacket)packet, remoteEndPoint);
+
+                        // Acknowledge the UseCircuitCode packet
+                        SendAckImmediate(remoteEndPoint, packet.Header.Sequence);
+                    }
+                );
+                return;
             }
 
             // Determine which agent this packet came from
@@ -558,11 +570,11 @@ namespace OpenSim.Region.ClientStack.LindenUDP
             // Stats tracking
             Interlocked.Increment(ref udpClient.PacketsReceived);
 
-            #region ACK Receiving
+            int now = Environment.TickCount & Int32.MaxValue;
-
-            int now = Environment.TickCount;
             udpClient.TickLastPacketReceived = now;
 
+            #region ACK Receiving
+
             // Handle appended ACKs
             if (packet.Header.AppendedAcks && packet.Header.AckList != null)
             {
@@ -650,6 +662,25 @@ namespace OpenSim.Region.ClientStack.LindenUDP
         {
         }
 
+        private void SendAckImmediate(IPEndPoint remoteEndpoint, uint sequenceNumber)
+        {
+            PacketAckPacket ack = new PacketAckPacket();
+            ack.Header.Reliable = false;
+            ack.Packets = new PacketAckPacket.PacketsBlock[1];
+            ack.Packets[0] = new PacketAckPacket.PacketsBlock();
+            ack.Packets[0].ID = sequenceNumber;
+
+            byte[] packetData = ack.ToBytes();
+            int length = packetData.Length;
+
+            UDPPacketBuffer buffer = new UDPPacketBuffer(remoteEndpoint, length);
+            buffer.DataLength = length;
+
+            Buffer.BlockCopy(packetData, 0, buffer.Data, 0, length);
+
+            AsyncBeginSend(buffer);
+        }
+
         private bool IsClientAuthorized(UseCircuitCodePacket useCircuitCode, out AuthenticateResponse sessionInfo)
         {
             UUID agentID = useCircuitCode.CircuitCode.ID;

OpenSim/Region/ClientStack/LindenUDP/UnackedPacketCollection.cs

@@ -85,6 +85,8 @@ namespace OpenSim.Region.ClientStack.LindenUDP
         /// <param name="sequenceNumber">Sequence number of the packet to
         /// acknowledge</param>
         /// <param name="currentTime">Current value of Environment.TickCount</param>
+        /// <remarks>This does not immediately acknowledge the packet, it only
+        /// queues the ack so it can be handled in a thread-safe way later</remarks>
         public void Remove(uint sequenceNumber, int currentTime, bool fromResend)
         {
             m_pendingRemoves.Enqueue(new PendingAck(sequenceNumber, currentTime, fromResend));
@@ -108,7 +110,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 
             if (m_packets.Count > 0)
             {
-                int now = Environment.TickCount;
+                int now = Environment.TickCount & Int32.MaxValue;
 
                 foreach (OutgoingPacket packet in m_packets.Values)
                 {
@@ -123,10 +125,10 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                             expiredPackets = new List<OutgoingPacket>();
                         expiredPackets.Add(packet);
                     }
-                    else
+                    /*else
                     {
                         break;
-                    }
+                    }*/
                 }
             }