From a4017ee1eb30af8af4ac08c8003a796fcdd6f4a8 Mon Sep 17 00:00:00 2001
From: Justin Clark-Casey (justincc)
Date: Mon, 27 Jan 2014 23:47:43 +0000
Subject: Reinsert attachments list taking code in SP.MakeRootAgent()

Locking attachments then launching script instances on a separate thread will not work, attachments will simply be unlocked and vulnerable to race conditions.
---
 OpenSim/Region/Framework/Scenes/ScenePresence.cs | 44 ++++++++++++++++--------
 1 file changed, 30 insertions(+), 14 deletions(-)

(limited to 'OpenSim/Region/Framework/Scenes/ScenePresence.cs')

diff --git a/OpenSim/Region/Framework/Scenes/ScenePresence.cs b/OpenSim/Region/Framework/Scenes/ScenePresence.cs
index 0cc00ed..84201cc 100644
--- a/OpenSim/Region/Framework/Scenes/ScenePresence.cs
+++ b/OpenSim/Region/Framework/Scenes/ScenePresence.cs
@@ -1190,22 +1190,36 @@ namespace OpenSim.Region.Framework.Scenes
                 // and CHANGED_REGION) when the attachments have been rezzed in the new region.  This cannot currently
                 // be done in AttachmentsModule.CopyAttachments(AgentData ad, IScenePresence sp) itself since we are
                 // not transporting the required data.
-                lock (m_attachments)
+                //
+                // We need to restart scripts here so that they receive the correct changed events (CHANGED_TELEPORT
+                // and CHANGED_REGION) when the attachments have been rezzed in the new region.  This cannot currently
+                // be done in AttachmentsModule.CopyAttachments(AgentData ad, IScenePresence sp) itself since we are
+                // not transporting the required data.
+                //
+                // We must take a copy of the attachments list here (rather than locking) to avoid a deadlock where a script in one of 
+                // the attachments may start processing an event (which locks ScriptInstance.m_Script) that then calls a method here
+                // which needs to lock m_attachments.  ResumeScripts() needs to take a ScriptInstance.m_Script lock to try to unset the Suspend status.
+                //
+                // FIXME: In theory, this deadlock should not arise since scripts should not be processing events until ResumeScripts().
+                // But XEngine starts all scripts unsuspended.  Starting them suspended will not currently work because script rezzing
+                // is placed in an asynchronous queue in XEngine and so the ResumeScripts() call will almost certainly execute before the 
+                // script is rezzed.  This means the ResumeScripts() does absolutely nothing when using XEngine.
+                //
+                // One cannot simply iterate over attachments in a fire and forget thread because this would no longer
+                // be locked, allowing race conditions if other code changes the attachments list.
+                List<SceneObjectGroup> attachments = GetAttachments();
+
+                if (attachments.Count > 0)
                 {
-                    if (HasAttachments())
-                    {
-                        m_log.DebugFormat(
-                            "[SCENE PRESENCE]: Restarting scripts in attachments for {0} in {1}", Name, Scene.Name);
+                    m_log.DebugFormat(
+                        "[SCENE PRESENCE]: Restarting scripts in attachments for {0} in {1}", Name, Scene.Name);
 
-                        // Resume scripts
-                        Util.FireAndForget(delegate(object x) {
-                            foreach (SceneObjectGroup sog in m_attachments)
-                            {
-                                sog.ScheduleGroupForFullUpdate();
-                                sog.RootPart.ParentGroup.CreateScriptInstances(0, false, m_scene.DefaultScriptEngine, GetStateSource());
-                                sog.ResumeScripts();
-                            }
-                        });
+                    // Resume scripts
+                    foreach (SceneObjectGroup sog in attachments)
+                    {
+                        sog.ScheduleGroupForFullUpdate();
+                        sog.RootPart.ParentGroup.CreateScriptInstances(0, false, m_scene.DefaultScriptEngine, GetStateSource());
+                        sog.ResumeScripts();
                     }
                 }
             }
@@ -3227,6 +3241,8 @@ namespace OpenSim.Region.Framework.Scenes
             // again here... this comes after the cached appearance check because the avatars
             // appearance goes into the avatar update packet
             SendAvatarDataToAllAgents();
+
+            // This invocation always shows up in the viewer logs as an error.  Is it needed?
             SendAppearanceToAgent(this);
 
             // If we are using the the cached appearance then send it out to everyone
-- 
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