From b3d152f3ba5cb07c005b0163c752f2c0f97c0034 Mon Sep 17 00:00:00 2001
From: "Justin Clark-Casey (justincc)" <jjustincc@googlemail.com>
Date: Fri, 10 Feb 2012 21:26:05 +0000
Subject: [PATCH] Fix an npc delete race condition with LSL sensors where an
 initial presence check could succeed but then the npc removed before the
 subequent npc check.

The resulting null would cause an exception.  We now check for null before looking at SenseAsAgent.
Hopefully fixes http://opensimulator.org/mantis/view.php?id=5872
---
 .../Implementation/Plugins/SensorRepeat.cs    | 29 +++++++++++++------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/OpenSim/Region/ScriptEngine/Shared/Api/Implementation/Plugins/SensorRepeat.cs b/OpenSim/Region/ScriptEngine/Shared/Api/Implementation/Plugins/SensorRepeat.cs
index 3e0e452ce0..850f50b13d 100644
--- a/OpenSim/Region/ScriptEngine/Shared/Api/Implementation/Plugins/SensorRepeat.cs
+++ b/OpenSim/Region/ScriptEngine/Shared/Api/Implementation/Plugins/SensorRepeat.cs
@@ -445,17 +445,28 @@ namespace OpenSim.Region.ScriptEngine.Shared.Api.Plugins
             Vector3 toRegionPos;
             double dis;
 
-            Action<ScenePresence> senseEntity = new Action<ScenePresence>(delegate(ScenePresence presence)
+            Action<ScenePresence> senseEntity = new Action<ScenePresence>(presence =>
             {
-                if ((ts.type & NPC) == 0
-                    && presence.PresenceType == PresenceType.Npc
-                    && !npcModule.GetNPC(presence.UUID, presence.Scene).SenseAsAgent)
-                    return;
+                if ((ts.type & NPC) == 0 && presence.PresenceType == PresenceType.Npc)
+                {
+                    INPC npcData = npcModule.GetNPC(presence.UUID, presence.Scene);
+                    if (npcData == null || !npcData.SenseAsAgent)
+                        return;
+                }
 
-                if ((ts.type & AGENT) == 0
-                    && (presence.PresenceType == PresenceType.User
-                        || npcModule.GetNPC(presence.UUID, presence.Scene).SenseAsAgent))
-                    return;
+                if ((ts.type & AGENT) == 0)
+                {
+                    if (presence.PresenceType == PresenceType.User)
+                    {
+                        return;
+                    }
+                    else
+                    {
+                        INPC npcData = npcModule.GetNPC(presence.UUID, presence.Scene);
+                        if (npcData != null && npcData.SenseAsAgent)
+                            return;
+                    }
+                }
 
                 if (presence.IsDeleted || presence.IsChildAgent || presence.GodLevel > 0.0)
                     return;