UnackedPacketCollection.cs

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using System;
using System.Collections.Generic;
using System.Net;
using System.Threading;
using OpenMetaverse;

//using System.Reflection;
//using log4net;

namespace OpenSim.Region.ClientStack.LindenUDP
{
    public sealed class UnackedPacketCollection
    {
        private struct PendingAck
        {
            public uint SequenceNumber;
            public int RemoveTime;
            public bool FromResend;

            public PendingAck(uint sequenceNumber, int currentTime, bool fromResend)
            {
                SequenceNumber = sequenceNumber;
                RemoveTime = currentTime;
                FromResend = fromResend;
            }
        }

        //private static readonly ILog m_log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);

        private Dictionary<uint, OutgoingPacket> m_packets = new Dictionary<uint, OutgoingPacket>();
        private LocklessQueue<OutgoingPacket> m_pendingAdds = new LocklessQueue<OutgoingPacket>();
        private LocklessQueue<PendingAck> m_pendingAcknowledgements = new LocklessQueue<PendingAck>();
        private LocklessQueue<uint> m_pendingRemoves = new LocklessQueue<uint>();

        public void Add(OutgoingPacket packet)
        {
            m_pendingAdds.Enqueue(packet);
            Interlocked.Add(ref packet.Client.UnackedBytes, packet.Buffer.DataLength);            
        }

        public void Acknowledge(uint sequenceNumber, int currentTime, bool fromResend)
        {
            m_pendingAcknowledgements.Enqueue(new PendingAck(sequenceNumber, currentTime, fromResend));
        }

        public void Remove(uint sequenceNumber)
        {
            m_pendingRemoves.Enqueue(sequenceNumber);
        }

        public List<OutgoingPacket> GetExpiredPackets(int timeoutMS)
        {
            ProcessQueues();

            List<OutgoingPacket> expiredPackets = null;

            if (m_packets.Count > 0)
            {
                int now = Environment.TickCount & Int32.MaxValue;

                foreach (OutgoingPacket packet in m_packets.Values)
                {
                    // TickCount of zero means a packet is in the resend queue 
                    // but hasn't actually been sent over the wire yet
                    if (packet.TickCount == 0)
                        continue;

                    if (now - packet.TickCount >= timeoutMS)
                    {
                        if (expiredPackets == null)
                            expiredPackets = new List<OutgoingPacket>();

                        // The TickCount will be set to the current time when the packet
                        // is actually sent out again
                        packet.TickCount = 0;

                        // As with other network applications, assume that an expired packet is
                        // an indication of some network problem, slow transmission
                        packet.Client.FlowThrottle.ExpirePackets(1);
                        
                        expiredPackets.Add(packet);
                    }
                }
            }

            // if (expiredPackets != null)
            //     m_log.DebugFormat("[UNACKED PACKET COLLECTION]: Found {0} expired packets on timeout of {1}", expiredPackets.Count, timeoutMS);

            return expiredPackets;
        }

        private void ProcessQueues()
        {
            // Process all the pending adds
            OutgoingPacket pendingAdd;
            while (m_pendingAdds.TryDequeue(out pendingAdd))
                if (pendingAdd != null)
                    m_packets[pendingAdd.SequenceNumber] = pendingAdd;
            
            // Process all the pending removes, including updating statistics and round-trip times
            PendingAck pendingAcknowledgement;
            while (m_pendingAcknowledgements.TryDequeue(out pendingAcknowledgement))
            {
                //m_log.DebugFormat("[UNACKED PACKET COLLECTION]: Processing ack {0}", pendingAcknowledgement.SequenceNumber);
                OutgoingPacket ackedPacket;
                if (m_packets.TryGetValue(pendingAcknowledgement.SequenceNumber, out ackedPacket))
                {
                    if (ackedPacket != null)
                    {
                        m_packets.Remove(pendingAcknowledgement.SequenceNumber);

                        // As with other network applications, assume that an acknowledged packet is an
                        // indication that the network can handle a little more load, speed up the transmission
                        ackedPacket.Client.FlowThrottle.AcknowledgePackets(1);

                        // Update stats
                        Interlocked.Add(ref ackedPacket.Client.UnackedBytes, -ackedPacket.Buffer.DataLength);

                        if (!pendingAcknowledgement.FromResend)
                        {
                            // Calculate the round-trip time for this packet and its ACK
                            int rtt = pendingAcknowledgement.RemoveTime - ackedPacket.TickCount;
                            if (rtt > 0)
                                ackedPacket.Client.UpdateRoundTrip(rtt);
                        }
                    }
                    else
                    {
                        // m_log.WarnFormat("[UNACKED PACKET COLLECTION]: found null packet for sequence number {0} to ack",
                        //                  pendingAcknowledgement.SequenceNumber);
                    }
                }
                else
                {
                    // m_log.WarnFormat("[UNACKED PACKET COLLECTION]: Could not find packet with sequence number {0} to ack",
                    //                  pendingAcknowledgement.SequenceNumber);                    
                }
            }

            uint pendingRemove;
            while(m_pendingRemoves.TryDequeue(out pendingRemove))
            {
                OutgoingPacket removedPacket;
                if (m_packets.TryGetValue(pendingRemove, out removedPacket))
                {
                    if (removedPacket != null)
                    {
                        m_packets.Remove(pendingRemove);

                        // Update stats
                        Interlocked.Add(ref removedPacket.Client.UnackedBytes, -removedPacket.Buffer.DataLength);
                    }
                }
            }
        }
    }
}