8 files changed, 268 insertions, 134 deletions

diff --git a/OpenSim/Region/ClientStack/Linden/Caps/EventQueue/Tests/EventQueueTests.cs b/OpenSim/Region/ClientStack/Linden/Caps/EventQueue/Tests/EventQueueTests.cs
index 141af8a..626932f 100644
--- a/OpenSim/Region/ClientStack/Linden/Caps/EventQueue/Tests/EventQueueTests.cs
+++ b/OpenSim/Region/ClientStack/Linden/Caps/EventQueue/Tests/EventQueueTests.cs
@@ -91,7 +91,7 @@ namespace OpenSim.Region.ClientStack.Linden.Tests
         public void RemoveForClient()
         {
             TestHelpers.InMethod();
-//            log4net.Config.XmlConfigurator.Configure();
+//            TestHelpers.EnableLogging();
 
             UUID spId = TestHelpers.ParseTail(0x1);
 
diff --git a/OpenSim/Region/ClientStack/Linden/UDP/LLClientView.cs b/OpenSim/Region/ClientStack/Linden/UDP/LLClientView.cs
index 0dbce2f..f0d8181 100644
--- a/OpenSim/Region/ClientStack/Linden/UDP/LLClientView.cs
+++ b/OpenSim/Region/ClientStack/Linden/UDP/LLClientView.cs
@@ -512,7 +512,13 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                 // We still perform a force close inside the sync lock since this is intended to attempt close where
                 // there is some unidentified connection problem, not where we have issues due to deadlock
                 if (!IsActive && !force)
+                {
+                    m_log.DebugFormat(
+                        "[CLIENT]: Not attempting to close inactive client {0} in {1} since force flag is not set", 
+                        Name, m_scene.Name);
+
                     return;
+                }
 
                 IsActive = false;
                 CloseWithoutChecks();
diff --git a/OpenSim/Region/ClientStack/Linden/UDP/LLUDPServer.cs b/OpenSim/Region/ClientStack/Linden/UDP/LLUDPServer.cs
index 5c38399..de2f9d4 100644
--- a/OpenSim/Region/ClientStack/Linden/UDP/LLUDPServer.cs
+++ b/OpenSim/Region/ClientStack/Linden/UDP/LLUDPServer.cs
@@ -1799,9 +1799,9 @@ namespace OpenSim.Region.ClientStack.LindenUDP
     
                 if (!client.SceneAgent.IsChildAgent)
                      client.Kick("Simulator logged you out due to connection timeout.");
-    
-                client.CloseWithoutChecks();
             }
+
+            m_scene.IncomingCloseAgent(client.AgentId, true);
         }
 
         private void IncomingPacketHandler()
@@ -2142,7 +2142,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
             if (!client.IsLoggingOut)
             {
                 client.IsLoggingOut = true;
-                client.Close();
+                m_scene.IncomingCloseAgent(client.AgentId, false);
             }
         }
     }
diff --git a/OpenSim/Region/ClientStack/Linden/UDP/Tests/BasicCircuitTests.cs b/OpenSim/Region/ClientStack/Linden/UDP/Tests/BasicCircuitTests.cs
index b47ff54..9700224 100644
--- a/OpenSim/Region/ClientStack/Linden/UDP/Tests/BasicCircuitTests.cs
+++ b/OpenSim/Region/ClientStack/Linden/UDP/Tests/BasicCircuitTests.cs
@@ -200,7 +200,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP.Tests
         public void TestLogoutClientDueToAck()
         {
             TestHelpers.InMethod();
-//            TestHelpers.EnableLogging();
+            TestHelpers.EnableLogging();
 
             IniConfigSource ics = new IniConfigSource();
             IConfig config = ics.AddConfig("ClientStack.LindenUDP");
diff --git a/OpenSim/Region/CoreModules/Framework/EntityTransfer/EntityTransferModule.cs b/OpenSim/Region/CoreModules/Framework/EntityTransfer/EntityTransferModule.cs
index 01ef710..87f0264 100644
--- a/OpenSim/Region/CoreModules/Framework/EntityTransfer/EntityTransferModule.cs
+++ b/OpenSim/Region/CoreModules/Framework/EntityTransfer/EntityTransferModule.cs
@@ -1064,8 +1064,18 @@ namespace OpenSim.Region.CoreModules.Framework.EntityTransfer
             // Now let's make it officially a child agent
             sp.MakeChildAgent();
 
-            // Finally, let's close this previously-known-as-root agent, when the jump is outside the view zone
+            // May still need to signal neighbours whether child agents may need closing irrespective of whether this
+            // one needed closing.  Neighbour regions also contain logic to prevent a close if a subsequent move or
+            // teleport re-established the child connection.
+            // 
+            // It may be possible to also close child agents after a pause but one needs to be very careful about
+            // race conditions between different regions on rapid teleporting (e.g. from A1 to a non-neighbour B, back
+            // to a neighbour A2 then off to a non-neighbour C.  Also, closing child agents early may be more compatible
+            // with complicated scenarios where there a mixture of V1 and V2 teleports, though this is conjecture.  It's
+            // easier to close immediately and greatly reduce the scope of race conditions if possible.
+            sp.CloseChildAgents(newRegionX, newRegionY);
 
+            // Finally, let's close this previously-known-as-root agent, when the jump is outside the view zone
             if (NeedsClosing(sp.DrawDistance, oldRegionX, newRegionX, oldRegionY, newRegionY, reg))
             {
                 sp.DoNotCloseAfterTeleport = false;
@@ -1081,14 +1091,12 @@ namespace OpenSim.Region.CoreModules.Framework.EntityTransfer
                 if (!sp.DoNotCloseAfterTeleport)
                 {
                     // OK, it got this agent. Let's close everything
-                    m_log.DebugFormat("[ENTITY TRANSFER MODULE]: Closing in agent {0} in region {1}", sp.Name, Scene.Name);
-                    sp.CloseChildAgents(newRegionX, newRegionY);
+                    m_log.DebugFormat("[ENTITY TRANSFER MODULE]: Closing agent {0} in {1}", sp.Name, Scene.Name);
                     sp.Scene.IncomingCloseAgent(sp.UUID, false);
-
                 }
                 else
                 {
-                    m_log.DebugFormat("[ENTITY TRANSFER MODULE]: Not closing agent {0}, user is back in {0}", sp.Name, Scene.Name);
+                    m_log.DebugFormat("[ENTITY TRANSFER MODULE]: Not closing agent {0}, user is back in {1}", sp.Name, Scene.Name);
                     sp.DoNotCloseAfterTeleport = false;
                 }
             }
@@ -1863,10 +1871,10 @@ namespace OpenSim.Region.CoreModules.Framework.EntityTransfer
             List<ulong> newRegions = NewNeighbours(neighbourHandles, previousRegionNeighbourHandles);
             List<ulong> oldRegions = OldNeighbours(neighbourHandles, previousRegionNeighbourHandles);
 
-            //Dump("Current Neighbors", neighbourHandles);
-            //Dump("Previous Neighbours", previousRegionNeighbourHandles);
-            //Dump("New Neighbours", newRegions);
-            //Dump("Old Neighbours", oldRegions);
+//            Dump("Current Neighbors", neighbourHandles);
+//            Dump("Previous Neighbours", previousRegionNeighbourHandles);
+//            Dump("New Neighbours", newRegions);
+//            Dump("Old Neighbours", oldRegions);
 
             /// Update the scene presence's known regions here on this region
             sp.DropOldNeighbours(oldRegions);
@@ -1874,8 +1882,7 @@ namespace OpenSim.Region.CoreModules.Framework.EntityTransfer
             /// Collect as many seeds as possible
             Dictionary<ulong, string> seeds;
             if (sp.Scene.CapsModule != null)
-                seeds
-                    = new Dictionary<ulong, string>(sp.Scene.CapsModule.GetChildrenSeeds(sp.UUID));
+                seeds = new Dictionary<ulong, string>(sp.Scene.CapsModule.GetChildrenSeeds(sp.UUID));
             else
                 seeds = new Dictionary<ulong, string>();
 
@@ -1945,6 +1952,7 @@ namespace OpenSim.Region.CoreModules.Framework.EntityTransfer
                     newAgent = true;
                 else
                     newAgent = false;
+//                    continue;
 
                 if (neighbour.RegionHandle != sp.Scene.RegionInfo.RegionHandle)
                 {
diff --git a/OpenSim/Region/CoreModules/World/Estate/EstateManagementModule.cs b/OpenSim/Region/CoreModules/World/Estate/EstateManagementModule.cs
index 121b2aa..31547a6 100644
--- a/OpenSim/Region/CoreModules/World/Estate/EstateManagementModule.cs
+++ b/OpenSim/Region/CoreModules/World/Estate/EstateManagementModule.cs
@@ -562,7 +562,7 @@ namespace OpenSim.Region.CoreModules.World.Estate
                                 if (!Scene.TeleportClientHome(user, s.ControllingClient))
                                 {
                                     s.ControllingClient.Kick("Your access to the region was revoked and TP home failed - you have been logged out.");
-                                    s.ControllingClient.Close();
+                                    Scene.IncomingCloseAgent(s.UUID, false);
                                 }
                             }
                         }
@@ -797,7 +797,7 @@ namespace OpenSim.Region.CoreModules.World.Estate
                     if (!Scene.TeleportClientHome(prey, s.ControllingClient))
                     {
                         s.ControllingClient.Kick("You were teleported home by the region owner, but the TP failed - you have been logged out.");
-                        s.ControllingClient.Close();
+                        Scene.IncomingCloseAgent(s.UUID, false);
                     }
                 }
             }
@@ -820,7 +820,7 @@ namespace OpenSim.Region.CoreModules.World.Estate
                         if (!Scene.TeleportClientHome(p.UUID, p.ControllingClient))
                         {
                             p.ControllingClient.Kick("You were teleported home by the region owner, but the TP failed - you have been logged out.");
-                            p.ControllingClient.Close();
+                            Scene.IncomingCloseAgent(p.UUID, false);
                         }
                     }
                 }
diff --git a/OpenSim/Region/Framework/Scenes/Scene.cs b/OpenSim/Region/Framework/Scenes/Scene.cs
index b97a0f6..a3bd388 100644
--- a/OpenSim/Region/Framework/Scenes/Scene.cs
+++ b/OpenSim/Region/Framework/Scenes/Scene.cs
@@ -151,7 +151,7 @@ namespace OpenSim.Region.Framework.Scenes
         public SynchronizeSceneHandler SynchronizeScene;
 
         /// <summary>
-        /// Used to prevent simultaneous calls to RemoveClient() for the same agent from interfering with each other.
+        /// Used to prevent simultaneous calls to code that adds and removes agents.
         /// </summary>
         private object m_removeClientLock = new object();
 
@@ -1312,7 +1312,7 @@ namespace OpenSim.Region.Framework.Scenes
             Thread.Sleep(500);
 
             // Stop all client threads.
-            ForEachScenePresence(delegate(ScenePresence avatar) { avatar.ControllingClient.Close(); });
+            ForEachScenePresence(delegate(ScenePresence avatar) { IncomingCloseAgent(avatar.UUID, false); });
 
             m_log.Debug("[SCENE]: Persisting changed objects");
             EventManager.TriggerSceneShuttingDown(this);
@@ -2972,7 +2972,7 @@ namespace OpenSim.Region.Framework.Scenes
                         {
                             PresenceService.LogoutAgent(sp.ControllingClient.SessionId);
 
-                            sp.ControllingClient.Close();
+                            IncomingCloseAgent(sp.UUID, false);
                         }
                         else
                         {
@@ -3384,47 +3384,48 @@ namespace OpenSim.Region.Framework.Scenes
 
         public override void RemoveClient(UUID agentID, bool closeChildAgents)
         {
-//            CheckHeartbeat();
-            bool isChildAgent = false;
-            AgentCircuitData acd;
+            AgentCircuitData acd = m_authenticateHandler.GetAgentCircuitData(agentID);
 
-            lock (m_removeClientLock)
+            // Shouldn't be necessary since RemoveClient() is currently only called by IClientAPI.Close() which 
+            // in turn is only called by Scene.IncomingCloseAgent() which checks whether the presence exists or not
+            // However, will keep for now just in case.
+            if (acd == null)
             {
-                acd = m_authenticateHandler.GetAgentCircuitData(agentID);
+                m_log.ErrorFormat(
+                    "[SCENE]: No agent circuit found for {0} in {1}, aborting Scene.RemoveClient", agentID, Name);
 
-                if (acd == null)
-                {
-                    m_log.ErrorFormat("[SCENE]: No agent circuit found for {0}, aborting Scene.RemoveClient", agentID);
-                    return;
-                }
-                else
-                {
-                    // We remove the acd up here to avoid later race conditions if two RemoveClient() calls occurred
-                    // simultaneously.
-                    // We also need to remove by agent ID since NPCs will have no circuit code.
-                    m_authenticateHandler.RemoveCircuit(agentID);
-                }
+                return;
+            }
+            else
+            {
+                m_authenticateHandler.RemoveCircuit(agentID);
             }
 
+            // TODO: Can we now remove this lock?
             lock (acd)
-            {
+            {    
+                bool isChildAgent = false;
+
                 ScenePresence avatar = GetScenePresence(agentID);
-    
+ 
+                // Shouldn't be necessary since RemoveClient() is currently only called by IClientAPI.Close() which 
+                // in turn is only called by Scene.IncomingCloseAgent() which checks whether the presence exists or not
+                // However, will keep for now just in case.
                 if (avatar == null)
                 {
-                    m_log.WarnFormat(
+                    m_log.ErrorFormat(
                         "[SCENE]: Called RemoveClient() with agent ID {0} but no such presence is in the scene.", agentID);
     
                     return;
                 }
-    
+
                 try
                 {
                     isChildAgent = avatar.IsChildAgent;
 
                     m_log.DebugFormat(
                         "[SCENE]: Removing {0} agent {1} {2} from {3}",
-                        (isChildAgent ? "child" : "root"), avatar.Name, agentID, RegionInfo.RegionName);
+                        isChildAgent ? "child" : "root", avatar.Name, agentID, Name);
     
                     // Don't do this to root agents, it's not nice for the viewer
                     if (closeChildAgents && isChildAgent)
@@ -3587,13 +3588,13 @@ namespace OpenSim.Region.Framework.Scenes
         /// is activated later when the viewer sends the initial UseCircuitCodePacket UDP packet (in the case of
         /// the LLUDP stack).
         /// </remarks>
-        /// <param name="agent">CircuitData of the agent who is connecting</param>
+        /// <param name="acd">CircuitData of the agent who is connecting</param>
         /// <param name="reason">Outputs the reason for the false response on this string</param>
         /// <param name="requirePresenceLookup">True for normal presence. False for NPC
         /// or other applications where a full grid/Hypergrid presence may not be required.</param>
         /// <returns>True if the region accepts this agent.  False if it does not.  False will 
         /// also return a reason.</returns>
-        public bool NewUserConnection(AgentCircuitData agent, uint teleportFlags, out string reason, bool requirePresenceLookup)
+        public bool NewUserConnection(AgentCircuitData acd, uint teleportFlags, out string reason, bool requirePresenceLookup)
         {
             bool vialogin = ((teleportFlags & (uint)TPFlags.ViaLogin) != 0 ||
                 (teleportFlags & (uint)TPFlags.ViaHGLogin) != 0);
@@ -3613,15 +3614,15 @@ namespace OpenSim.Region.Framework.Scenes
             m_log.DebugFormat(
                 "[SCENE]: Region {0} told of incoming {1} agent {2} {3} {4} (circuit code {5}, IP {6}, viewer {7}, teleportflags ({8}), position {9})",
                 RegionInfo.RegionName,
-                (agent.child ? "child" : "root"),
-                agent.firstname,
-                agent.lastname,
-                agent.AgentID,
-                agent.circuitcode,
-                agent.IPAddress,
-                agent.Viewer,
+                (acd.child ? "child" : "root"),
+                acd.firstname,
+                acd.lastname,
+                acd.AgentID,
+                acd.circuitcode,
+                acd.IPAddress,
+                acd.Viewer,
                 ((TPFlags)teleportFlags).ToString(),
-                agent.startpos
+                acd.startpos
             );
 
             if (!LoginsEnabled)
@@ -3639,7 +3640,7 @@ namespace OpenSim.Region.Framework.Scenes
             {
                 foreach (string viewer in m_AllowedViewers)
                 {
-                    if (viewer == agent.Viewer.Substring(0, viewer.Length).Trim().ToLower())
+                    if (viewer == acd.Viewer.Substring(0, viewer.Length).Trim().ToLower())
                     {
                         ViewerDenied = false;
                         break;
@@ -3656,7 +3657,7 @@ namespace OpenSim.Region.Framework.Scenes
             {
                 foreach (string viewer in m_BannedViewers)
                 {
-                    if (viewer == agent.Viewer.Substring(0, viewer.Length).Trim().ToLower())
+                    if (viewer == acd.Viewer.Substring(0, viewer.Length).Trim().ToLower())
                     {
                         ViewerDenied = true;
                         break;
@@ -3668,61 +3669,112 @@ namespace OpenSim.Region.Framework.Scenes
             {
                 m_log.DebugFormat(
                     "[SCENE]: Access denied for {0} {1} using {2}",
-                    agent.firstname, agent.lastname, agent.Viewer);
+                    acd.firstname, acd.lastname, acd.Viewer);
                 reason = "Access denied, your viewer is banned by the region owner";
                 return false;
             }
 
             ILandObject land;
+            ScenePresence sp;
 
-            lock (agent)
+            lock (m_removeClientLock)
             {
-                ScenePresence sp = GetScenePresence(agent.AgentID);
-    
-                if (sp != null)
+                sp = GetScenePresence(acd.AgentID);
+
+                // We need to ensure that we are not already removing the scene presence before we ask it not to be 
+                // closed.
+                if (sp != null && sp.IsChildAgent && sp.LifecycleState == ScenePresenceState.Running)
                 {
-                    if (!sp.IsChildAgent)
-                    {
-                        // We have a root agent. Is it in transit?
-                        if (!EntityTransferModule.IsInTransit(sp.UUID))
-                        {
-                            // We have a zombie from a crashed session. 
-                            // Or the same user is trying to be root twice here, won't work.
-                            // Kill it.
-                            m_log.WarnFormat(
-                                "[SCENE]: Existing root scene presence detected for {0} {1} in {2} when connecting.  Removing existing presence.",
-                                sp.Name, sp.UUID, RegionInfo.RegionName);
+                    m_log.DebugFormat(
+                        "[SCENE]: Reusing existing child scene presence for {0} in {1}", sp.Name, Name);
 
-                            if (sp.ControllingClient != null)
-                                sp.ControllingClient.Close(true);
+                    // In the case where, for example, an A B C D region layout, an avatar may
+                    // teleport from A -> D, but then -> C before A has asked B to close its old child agent.  When C
+                    // renews the lease on the child agent at B, we must make sure that the close from A does not succeed.
+                    if (!acd.ChildrenCapSeeds.ContainsKey(RegionInfo.RegionHandle))
+                    {
+                        m_log.DebugFormat(
+                            "[SCENE]: Setting DoNotCloseAfterTeleport for child scene presence {0} in {1} because source will attempt close.", 
+                            sp.Name, Name);
 
-                            sp = null;
-                        }
-                        //else
-                        //    m_log.WarnFormat("[SCENE]: Existing root scene presence for {0} {1} in {2}, but agent is in trasit", sp.Name, sp.UUID, RegionInfo.RegionName);
+                        sp.DoNotCloseAfterTeleport = true;
                     }
-                    else
+                    else if (EntityTransferModule.IsInTransit(sp.UUID))
                     {
-                        // We have a child agent here
+                        m_log.DebugFormat(
+                            "[SCENE]: Setting DoNotCloseAfterTeleport for child scene presence {0} in {1} because this region will attempt previous end-of-teleport close.", 
+                            sp.Name, Name);
+
                         sp.DoNotCloseAfterTeleport = true;
-                        //m_log.WarnFormat("[SCENE]: Existing child scene presence for {0} {1} in {2}", sp.Name, sp.UUID, RegionInfo.RegionName);
                     }
                 }
+            }
+
+            // Need to poll here in case we are currently deleting an sp.  Letting threads run over each other will
+            // allow unpredictable things to happen.
+            if (sp != null)
+            {
+                const int polls = 10;
+                const int pollInterval = 1000;
+                int pollsLeft = polls;
+
+                while (sp.LifecycleState == ScenePresenceState.Removing && pollsLeft-- > 0)
+                    Thread.Sleep(pollInterval);
+
+                if (sp.LifecycleState == ScenePresenceState.Removing)
+                {
+                    m_log.WarnFormat(
+                        "[SCENE]: Agent {0} in {1} was still being removed after {2}s.  Aborting NewUserConnection.", 
+                        sp.Name, Name, polls * pollInterval / 1000);
+
+                    return false;
+                }
+                else if (polls != pollsLeft)
+                {
+                    m_log.DebugFormat(
+                        "[SCENE]: NewUserConnection for agent {0} in {1} had to wait {2}s for in-progress removal to complete on an old presence.",
+                        sp.Name, Name, polls * pollInterval / 1000);
+                }
+            }
+
+            // TODO: can we remove this lock?
+            lock (acd)
+            {
+                if (sp != null && !sp.IsChildAgent)
+                {
+                    // We have a root agent. Is it in transit?
+                    if (!EntityTransferModule.IsInTransit(sp.UUID))
+                    {
+                        // We have a zombie from a crashed session. 
+                        // Or the same user is trying to be root twice here, won't work.
+                        // Kill it.
+                        m_log.WarnFormat(
+                            "[SCENE]: Existing root scene presence detected for {0} {1} in {2} when connecting.  Removing existing presence.",
+                            sp.Name, sp.UUID, RegionInfo.RegionName);
+
+                        if (sp.ControllingClient != null)
+                            IncomingCloseAgent(sp.UUID, true);
+
+                        sp = null;
+                    }
+                    //else
+                    //    m_log.WarnFormat("[SCENE]: Existing root scene presence for {0} {1} in {2}, but agent is in trasit", sp.Name, sp.UUID, RegionInfo.RegionName);
+                }
 
                 // Optimistic: add or update the circuit data with the new agent circuit data and teleport flags.
                 // We need the circuit data here for some of the subsequent checks. (groups, for example)
                 // If the checks fail, we remove the circuit.
-                agent.teleportFlags = teleportFlags;
-                m_authenticateHandler.AddNewCircuit(agent.circuitcode, agent);
+                acd.teleportFlags = teleportFlags;
+                m_authenticateHandler.AddNewCircuit(acd.circuitcode, acd);
 
-                land = LandChannel.GetLandObject(agent.startpos.X, agent.startpos.Y);
+                land = LandChannel.GetLandObject(acd.startpos.X, acd.startpos.Y);
     
                 // On login test land permisions
                 if (vialogin)
                 {
-                    if (land != null && !TestLandRestrictions(agent.AgentID, out reason, ref agent.startpos.X, ref agent.startpos.Y))
+                    if (land != null && !TestLandRestrictions(acd.AgentID, out reason, ref acd.startpos.X, ref acd.startpos.Y))
                     {
-                        m_authenticateHandler.RemoveCircuit(agent.circuitcode);
+                        m_authenticateHandler.RemoveCircuit(acd.circuitcode);
                         return false;
                     }
                 }
@@ -3733,9 +3785,9 @@ namespace OpenSim.Region.Framework.Scenes
                     {
                         try
                         {
-                            if (!VerifyUserPresence(agent, out reason))
+                            if (!VerifyUserPresence(acd, out reason))
                             {
-                                m_authenticateHandler.RemoveCircuit(agent.circuitcode);
+                                m_authenticateHandler.RemoveCircuit(acd.circuitcode);
                                 return false;
                             }
                         }
@@ -3744,16 +3796,16 @@ namespace OpenSim.Region.Framework.Scenes
                             m_log.ErrorFormat(
                                 "[SCENE]: Exception verifying presence {0}{1}", e.Message, e.StackTrace);
 
-                            m_authenticateHandler.RemoveCircuit(agent.circuitcode);
+                            m_authenticateHandler.RemoveCircuit(acd.circuitcode);
                             return false;
                         }
                     }
     
                     try
                     {
-                        if (!AuthorizeUser(agent, SeeIntoRegion, out reason))
+                        if (!AuthorizeUser(acd, SeeIntoRegion, out reason))
                         {
-                            m_authenticateHandler.RemoveCircuit(agent.circuitcode);
+                            m_authenticateHandler.RemoveCircuit(acd.circuitcode);
                             return false;
                         }
                     }
@@ -3762,19 +3814,19 @@ namespace OpenSim.Region.Framework.Scenes
                         m_log.ErrorFormat(
                             "[SCENE]: Exception authorizing user {0}{1}", e.Message, e.StackTrace);
 
-                        m_authenticateHandler.RemoveCircuit(agent.circuitcode);
+                        m_authenticateHandler.RemoveCircuit(acd.circuitcode);
                         return false;
                     }
     
                     m_log.InfoFormat(
                         "[SCENE]: Region {0} authenticated and authorized incoming {1} agent {2} {3} {4} (circuit code {5})",
-                        RegionInfo.RegionName, (agent.child ? "child" : "root"), agent.firstname, agent.lastname,
-                        agent.AgentID, agent.circuitcode);
+                        Name, (acd.child ? "child" : "root"), acd.firstname, acd.lastname,
+                        acd.AgentID, acd.circuitcode);
     
                     if (CapsModule != null)
                     {
-                        CapsModule.SetAgentCapsSeeds(agent);
-                        CapsModule.CreateCaps(agent.AgentID);
+                        CapsModule.SetAgentCapsSeeds(acd);
+                        CapsModule.CreateCaps(acd.AgentID);
                     }
                 }
                 else
@@ -3787,14 +3839,14 @@ namespace OpenSim.Region.Framework.Scenes
                     {
                         m_log.DebugFormat(
                             "[SCENE]: Adjusting known seeds for existing agent {0} in {1}",
-                            agent.AgentID, RegionInfo.RegionName);
+                            acd.AgentID, RegionInfo.RegionName);
     
                         sp.AdjustKnownSeeds();
 
                         if (CapsModule != null)
                         {
-                            CapsModule.SetAgentCapsSeeds(agent);
-                            CapsModule.CreateCaps(agent.AgentID);
+                            CapsModule.SetAgentCapsSeeds(acd);
+                            CapsModule.CreateCaps(acd.AgentID);
                         }
                     }
                 }
@@ -3802,23 +3854,23 @@ namespace OpenSim.Region.Framework.Scenes
                 // Try caching an incoming user name much earlier on to see if this helps with an issue
                 // where HG users are occasionally seen by others as "Unknown User" because their UUIDName
                 // request for the HG avatar appears to trigger before the user name is cached.
-                CacheUserName(null, agent);
+                CacheUserName(null, acd);
             }
 
             if (vialogin)
             {
 //                CleanDroppedAttachments();
 
-                if (TestBorderCross(agent.startpos, Cardinals.E))
+                if (TestBorderCross(acd.startpos, Cardinals.E))
                 {
-                    Border crossedBorder = GetCrossedBorder(agent.startpos, Cardinals.E);
-                    agent.startpos.X = crossedBorder.BorderLine.Z - 1;
+                    Border crossedBorder = GetCrossedBorder(acd.startpos, Cardinals.E);
+                    acd.startpos.X = crossedBorder.BorderLine.Z - 1;
                 }
 
-                if (TestBorderCross(agent.startpos, Cardinals.N))
+                if (TestBorderCross(acd.startpos, Cardinals.N))
                 {
-                    Border crossedBorder = GetCrossedBorder(agent.startpos, Cardinals.N);
-                    agent.startpos.Y = crossedBorder.BorderLine.Z - 1;
+                    Border crossedBorder = GetCrossedBorder(acd.startpos, Cardinals.N);
+                    acd.startpos.Y = crossedBorder.BorderLine.Z - 1;
                 }
 
                 //Mitigate http://opensimulator.org/mantis/view.php?id=3522
@@ -3828,39 +3880,39 @@ namespace OpenSim.Region.Framework.Scenes
                 {
                     lock (EastBorders)
                     {
-                        if (agent.startpos.X > EastBorders[0].BorderLine.Z)
+                        if (acd.startpos.X > EastBorders[0].BorderLine.Z)
                         {
                             m_log.Warn("FIX AGENT POSITION");
-                            agent.startpos.X = EastBorders[0].BorderLine.Z * 0.5f;
-                            if (agent.startpos.Z > 720)
-                                agent.startpos.Z = 720;
+                            acd.startpos.X = EastBorders[0].BorderLine.Z * 0.5f;
+                            if (acd.startpos.Z > 720)
+                                acd.startpos.Z = 720;
                         }
                     }
                     lock (NorthBorders)
                     {
-                        if (agent.startpos.Y > NorthBorders[0].BorderLine.Z)
+                        if (acd.startpos.Y > NorthBorders[0].BorderLine.Z)
                         {
                             m_log.Warn("FIX Agent POSITION");
-                            agent.startpos.Y = NorthBorders[0].BorderLine.Z * 0.5f;
-                            if (agent.startpos.Z > 720)
-                                agent.startpos.Z = 720;
+                            acd.startpos.Y = NorthBorders[0].BorderLine.Z * 0.5f;
+                            if (acd.startpos.Z > 720)
+                                acd.startpos.Z = 720;
                         }
                     }
                 } else
                 {
-                    if (agent.startpos.X > EastBorders[0].BorderLine.Z)
+                    if (acd.startpos.X > EastBorders[0].BorderLine.Z)
                     {
                         m_log.Warn("FIX AGENT POSITION");
-                        agent.startpos.X = EastBorders[0].BorderLine.Z * 0.5f;
-                        if (agent.startpos.Z > 720)
-                            agent.startpos.Z = 720;
+                        acd.startpos.X = EastBorders[0].BorderLine.Z * 0.5f;
+                        if (acd.startpos.Z > 720)
+                            acd.startpos.Z = 720;
                     }
-                    if (agent.startpos.Y > NorthBorders[0].BorderLine.Z)
+                    if (acd.startpos.Y > NorthBorders[0].BorderLine.Z)
                     {
                         m_log.Warn("FIX Agent POSITION");
-                        agent.startpos.Y = NorthBorders[0].BorderLine.Z * 0.5f;
-                        if (agent.startpos.Z > 720)
-                            agent.startpos.Z = 720;
+                        acd.startpos.Y = NorthBorders[0].BorderLine.Z * 0.5f;
+                        if (acd.startpos.Z > 720)
+                            acd.startpos.Z = 720;
                     }
                 }
 
@@ -3876,12 +3928,12 @@ namespace OpenSim.Region.Framework.Scenes
                     {
                         // We have multiple SpawnPoints, Route the agent to a random or sequential one
                         if (SpawnPointRouting == "random")
-                            agent.startpos = spawnpoints[Util.RandomClass.Next(spawnpoints.Count) - 1].GetLocation(
+                            acd.startpos = spawnpoints[Util.RandomClass.Next(spawnpoints.Count) - 1].GetLocation(
                                 telehub.AbsolutePosition,
                                 telehub.GroupRotation
                             );
                         else
-                            agent.startpos = spawnpoints[SpawnPoint()].GetLocation(
+                            acd.startpos = spawnpoints[SpawnPoint()].GetLocation(
                                 telehub.AbsolutePosition,
                                 telehub.GroupRotation
                             );
@@ -3889,7 +3941,7 @@ namespace OpenSim.Region.Framework.Scenes
                     else
                     {
                         // We have a single SpawnPoint and will route the agent to it
-                        agent.startpos = spawnpoints[0].GetLocation(telehub.AbsolutePosition, telehub.GroupRotation);
+                        acd.startpos = spawnpoints[0].GetLocation(telehub.AbsolutePosition, telehub.GroupRotation);
                     }
 
                     return true;
@@ -3900,7 +3952,7 @@ namespace OpenSim.Region.Framework.Scenes
                 {
                     if (land.LandData.LandingType == (byte)1 && land.LandData.UserLocation != Vector3.Zero)
                     {
-                        agent.startpos = land.LandData.UserLocation;
+                        acd.startpos = land.LandData.UserLocation;
                     }
                 }
             }
@@ -4360,11 +4412,51 @@ namespace OpenSim.Region.Framework.Scenes
         /// </param>
         public bool IncomingCloseAgent(UUID agentID, bool force)
         {
-            //m_log.DebugFormat("[SCENE]: Processing incoming close agent for {0}", agentID);
-            ScenePresence presence = m_sceneGraph.GetScenePresence(agentID);
-            if (presence != null)
+            ScenePresence sp;
+
+            lock (m_removeClientLock)
+            {
+                sp = GetScenePresence(agentID);
+    
+                if (sp == null)
+                {
+                    m_log.DebugFormat(
+                        "[SCENE]: Called RemoveClient() with agent ID {0} but no such presence is in {1}", 
+                        agentID, Name);
+    
+                    return false;
+                }
+
+                if (sp.LifecycleState != ScenePresenceState.Running)
+                {
+                    m_log.DebugFormat(
+                        "[SCENE]: Called RemoveClient() for {0} in {1} but presence is already in state {2}",
+                        sp.Name, Name, sp.LifecycleState);
+
+                    return false;
+                }
+
+                // We need to avoid a race condition where in, for example, an A B C D region layout, an avatar may
+                // teleport from A -> D, but then -> C before A has asked B to close its old child agent.  We do not
+                // want to obey this close since C may have renewed the child agent lease on B.
+                if (sp.DoNotCloseAfterTeleport)
+                {
+                    m_log.DebugFormat(
+                        "[SCENE]: Not closing {0} agent {1} in {2} since another simulator has re-established the child connection",
+                        sp.IsChildAgent ? "child" : "root", sp.Name, Name);
+
+                    // Need to reset the flag so that a subsequent close after another teleport can succeed.
+                    sp.DoNotCloseAfterTeleport = false;
+
+                    return false;
+                }
+
+                sp.LifecycleState = ScenePresenceState.Removing;
+            }
+
+            if (sp != null)
             {
-                presence.ControllingClient.Close(force);
+                sp.ControllingClient.Close(force);
                 return true;
             }
 
diff --git a/OpenSim/Region/Framework/Scenes/ScenePresence.cs b/OpenSim/Region/Framework/Scenes/ScenePresence.cs
index 1b8c276..aac80f7 100644
--- a/OpenSim/Region/Framework/Scenes/ScenePresence.cs
+++ b/OpenSim/Region/Framework/Scenes/ScenePresence.cs
@@ -74,6 +74,8 @@ namespace OpenSim.Region.Framework.Scenes
 
     public class ScenePresence : EntityBase, IScenePresence
     {
+        private static readonly ILog m_log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
+
 //        ~ScenePresence()
 //        {
 //            m_log.DebugFormat("[SCENE PRESENCE]: Destructor called on {0}", Name);
@@ -85,10 +87,27 @@ namespace OpenSim.Region.Framework.Scenes
                 m_scene.EventManager.TriggerScenePresenceUpdated(this);
         }
 
-        private static readonly ILog m_log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
-
         public PresenceType PresenceType { get; private set; }
 
+        private ScenePresenceStateMachine m_stateMachine;
+
+        /// <summary>
+        /// The current state of this presence.  Governs only the existence lifecycle.  See ScenePresenceStateMachine
+        /// for more details.
+        /// </summary>
+        public ScenePresenceState LifecycleState 
+        { 
+            get
+            {
+                return m_stateMachine.GetState();
+            }
+
+            set
+            {
+                m_stateMachine.SetState(value);
+            }
+        }
+
 //        private static readonly byte[] DEFAULT_TEXTURE = AvatarAppearance.GetDefaultTexture().GetBytes();
         private static readonly Array DIR_CONTROL_FLAGS = Enum.GetValues(typeof(Dir_ControlFlags));
         private static readonly Vector3 HEAD_ADJUSTMENT = new Vector3(0f, 0f, 0.3f);
@@ -766,7 +785,7 @@ namespace OpenSim.Region.Framework.Scenes
 
         public ScenePresence(
             IClientAPI client, Scene world, AvatarAppearance appearance, PresenceType type)
-        {
+        {            
             AttachmentsSyncLock = new Object();
             AllowMovement = true;
             IsChildAgent = true;
@@ -811,6 +830,8 @@ namespace OpenSim.Region.Framework.Scenes
             SetDirectionVectors();
 
             Appearance = appearance;
+
+            m_stateMachine = new ScenePresenceStateMachine(this);
         }
 
         public void RegisterToEvents()
@@ -879,7 +900,7 @@ namespace OpenSim.Region.Framework.Scenes
         /// </summary>
         public void MakeRootAgent(Vector3 pos, bool isFlying)
         {
-            m_log.DebugFormat(
+            m_log.InfoFormat(
                 "[SCENE]: Upgrading child to root agent for {0} in {1}",
                 Name, m_scene.RegionInfo.RegionName);
 
@@ -887,6 +908,11 @@ namespace OpenSim.Region.Framework.Scenes
 
             IsChildAgent = false;
 
+            // Must reset this here so that a teleport to a region next to an existing region does not keep the flag
+            // set and prevent the close of the connection on a subsequent re-teleport.
+            // Should not be needed if we are not trying to tell this region to close
+//            DoNotCloseAfterTeleport = false;
+
             IGroupsModule gm = m_scene.RequestModuleInterface<IGroupsModule>();
             if (gm != null)
                 Grouptitle = gm.GetGroupTitle(m_uuid);
@@ -3738,6 +3764,8 @@ namespace OpenSim.Region.Framework.Scenes
             // m_reprioritizationTimer.Dispose(); 
 
             RemoveFromPhysicalScene();
+
+            LifecycleState = ScenePresenceState.Removed;
         }
 
         public void AddAttachment(SceneObjectGroup gobj)