Improve teleport cancellation in some circumstances, though cancelling teleports is still not recommended.

Previously, hitting the cancel button on a teleport would cancel on the client side but the request was ignored on the server side.
Cancel would still work if the teleport failed in the early stages (e.g. because the destination never replied to early CreateAgent and UpdateAgent messages).
But if the teleport still completed after a delay here or later on, the viewer would become confused (usual symptom appears to be avatar being unable to move/reteleport).
This commit makes OpenSimulator obey cancellations which are received before it sends the TeleportFinish event queue message and does proper cleanup.
But cancellations received after this (which can happen even though the cancel button is removed as this messages comes on a different thread) can still result in a frozen avatar.
This looks extremely difficult and impossible to fix.
I can replicate the same problem on the Linden Lab grid by hitting cancel immediately after a teleport starts (a teleport which would otherwise quickly succeed).

1 files changed, 97 insertions, 27 deletions

diff --git a/OpenSim/Region/CoreModules/Framework/EntityTransfer/EntityTransferStateMachine.cs b/OpenSim/Region/CoreModules/Framework/EntityTransfer/EntityTransferStateMachine.cs
index d0cab49..24d81d9 100644
--- a/OpenSim/Region/CoreModules/Framework/EntityTransfer/EntityTransferStateMachine.cs
+++ b/OpenSim/Region/CoreModules/Framework/EntityTransfer/EntityTransferStateMachine.cs
@@ -51,8 +51,9 @@ namespace OpenSim.Region.CoreModules.Framework.EntityTransfer
     /// This is a state machine.
     ///
     /// [Entry]               => Preparing
-    /// Preparing             => { Transferring || CleaningUp || [Exit] }
-    /// Transferring          => { ReceivedAtDestination || CleaningUp }
+    /// Preparing             => { Transferring || Cancelling || CleaningUp || [Exit] }
+    /// Transferring          => { ReceivedAtDestination || Cancelling || CleaningUp }
+    /// Cancelling            => CleaningUp
     /// ReceivedAtDestination => CleaningUp
     /// CleaningUp            => [Exit]
     ///
@@ -64,7 +65,8 @@ namespace OpenSim.Region.CoreModules.Framework.EntityTransfer
         Preparing,              // The agent is being prepared for transfer
         Transferring,           // The agent is in the process of being transferred to a destination
         ReceivedAtDestination,  // The destination has notified us that the agent has been successfully received
-        CleaningUp              // The agent is being changed to child/removed after a transfer
+        CleaningUp,             // The agent is being changed to child/removed after a transfer
+        Cancelling              // The user has cancelled the teleport but we have yet to act upon this.
     }
 
     /// <summary>
@@ -115,42 +117,110 @@ namespace OpenSim.Region.CoreModules.Framework.EntityTransfer
         /// <param name='newState'></param>
         /// <returns></returns>
         /// <exception cref='Exception'>Illegal transitions will throw an Exception</exception>
-        internal void UpdateInTransit(UUID id, AgentTransferState newState)
+        internal bool UpdateInTransit(UUID id, AgentTransferState newState)
         {
+            bool transitionOkay = false;
+
+            // We don't want to throw an exception on cancel since this can come it at any time.
+            bool failIfNotOkay = true;
+
+            // Should be a failure message if failure is not okay.
+            string failureMessage = null;
+
+            AgentTransferState? oldState = null;
+
             lock (m_agentsInTransit)
             {
                 // Illegal to try and update an agent that's not actually in transit.
                 if (!m_agentsInTransit.ContainsKey(id))
-                    throw new Exception(
-                        string.Format(
-                            "Agent with ID {0} is not registered as in transit in {1}",
-                            id, m_mod.Scene.RegionInfo.RegionName));
-
-                AgentTransferState oldState = m_agentsInTransit[id];
+                {
+                    if (newState != AgentTransferState.Cancelling)
+                        failureMessage = string.Format(
+                                "Agent with ID {0} is not registered as in transit in {1}",
+                                id, m_mod.Scene.RegionInfo.RegionName);
+                    else
+                        failIfNotOkay = false;
+                }
+                else
+                {
+                    oldState = m_agentsInTransit[id];
 
-                bool transitionOkay = false;
+                    if (newState == AgentTransferState.CleaningUp && oldState != AgentTransferState.CleaningUp)
+                    {
+                        transitionOkay = true;
+                    }
+                    else if (newState == AgentTransferState.Transferring && oldState == AgentTransferState.Preparing)
+                    {
+                        transitionOkay = true;
+                    }
+                    else if (newState == AgentTransferState.ReceivedAtDestination && oldState == AgentTransferState.Transferring)
+                    {
+                        transitionOkay = true;
+                    }
+                    else
+                    {
+                        if (newState == AgentTransferState.Cancelling 
+                            && (oldState == AgentTransferState.Preparing || oldState == AgentTransferState.Transferring))
+                        {
+                            transitionOkay = true;
+                        }
+                        else
+                        {
+                            failIfNotOkay = false;
+                        }
+                    }
 
-                if (newState == AgentTransferState.CleaningUp && oldState != AgentTransferState.CleaningUp)
-                    transitionOkay = true;
-                else if (newState == AgentTransferState.Transferring && oldState == AgentTransferState.Preparing)
-                    transitionOkay = true;
-                else if (newState == AgentTransferState.ReceivedAtDestination && oldState == AgentTransferState.Transferring)
-                    transitionOkay = true;
+                    if (!transitionOkay)
+                        failureMessage 
+                            = string.Format(
+                                "Agent with ID {0} is not allowed to move from old transit state {1} to new state {2} in {3}",
+                                id, oldState, newState, m_mod.Scene.RegionInfo.RegionName);
+                }
 
                 if (transitionOkay)
+                {
                     m_agentsInTransit[id] = newState;
-                else
-                    throw new Exception(
-                        string.Format(
-                            "Agent with ID {0} is not allowed to move from old transit state {1} to new state {2} in {3}",
-                            id, oldState, newState, m_mod.Scene.RegionInfo.RegionName));
+
+//                    m_log.DebugFormat(
+//                        "[ENTITY TRANSFER STATE MACHINE]: Changed agent with id {0} from state {1} to {2} in {3}", 
+//                        id, oldState, newState, m_mod.Scene.Name);
+                }
+                else if (failIfNotOkay)
+                {
+                    throw new Exception(failureMessage);
+                }
+//                else
+//                {
+//                    if (oldState != null)
+//                        m_log.DebugFormat(
+//                            "[ENTITY TRANSFER STATE MACHINE]: Ignored change of agent with id {0} from state {1} to {2} in {3}", 
+//                            id, oldState, newState, m_mod.Scene.Name);
+//                    else
+//                        m_log.DebugFormat(
+//                            "[ENTITY TRANSFER STATE MACHINE]: Ignored change of agent with id {0} to state {1} in {2} since agent not in transit", 
+//                            id, newState, m_mod.Scene.Name);
+//                }
             }
+
+            return transitionOkay;
         }
 
-        internal bool IsInTransit(UUID id)
+        /// <summary>
+        /// Gets the current agent transfer state.
+        /// </summary>
+        /// <returns>Null if the agent is not in transit</returns>
+        /// <param name='id'>
+        /// Identifier.
+        /// </param>
+        internal AgentTransferState? GetAgentTransferState(UUID id)
         {
             lock (m_agentsInTransit)
-                return m_agentsInTransit.ContainsKey(id);
+            {
+                if (!m_agentsInTransit.ContainsKey(id))
+                    return null;
+                else
+                    return m_agentsInTransit[id];
+            }
         }
 
         /// <summary>
@@ -203,14 +273,14 @@ namespace OpenSim.Region.CoreModules.Framework.EntityTransfer
             
             lock (m_agentsInTransit)
             {
-                if (!IsInTransit(id))
+                AgentTransferState? currentState = GetAgentTransferState(id);
+
+                if (currentState == null)
                     throw new Exception(
                         string.Format(
                             "Asked to wait for destination callback for agent with ID {0} in {1} but agent is not in transit",
                             id, m_mod.Scene.RegionInfo.RegionName));
 
-                AgentTransferState currentState = m_agentsInTransit[id];
-
                 if (currentState != AgentTransferState.Transferring && currentState != AgentTransferState.ReceivedAtDestination)
                     throw new Exception(
                         string.Format(