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Avoid a deadlock where a script can attempt to take a ScriptInstance.m_Scripts lock then a lock on SP.m_attachments whilst SP.MakeRootAgent() attempts to take in the opposite order. 

This is because scripts (at least on XEngine) start unsuspended - deceptively the ResumeScripts() calls in various places in the code are actually completely redundant (and useless).
The solution chosen here is to use a copy of the SP attachments and not have the list locked whilst creating the scripts when an avatar enters the region.
This looks to address http://opensimulator.org/mantis/view.php?id=6557
cpu-performance
Justin Clark-Casey (justincc) 2013-06-05 22:20:48 +01:00
parent b5d0ac4c42
commit f41fc4eb25
1 changed files with 22 additions and 12 deletions
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20
OpenSim/Region/Framework/Scenes/ScenePresence.cs
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@ -121,6 +121,8 @@ namespace OpenSim.Region.Framework.Scenes
/// <remarks>
/// TODO: For some reason, we effectively have a list both here and in Appearance. Need to work out if this is
/// necessary.
/// NOTE: To avoid deadlocks, do not lock m_attachments and then perform other tasks under that lock. Take a copy
/// of the list and act on that instead.
/// </remarks>
private List<SceneObjectGroup> m_attachments = new List<SceneObjectGroup>();
@ -971,22 +973,30 @@ 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)
{
if (HasAttachments())
//
// 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.
List<SceneObjectGroup> attachments = GetAttachments();
if (attachments.Count > 0)
{
m_log.DebugFormat(
"[SCENE PRESENCE]: Restarting scripts in attachments for {0} in {1}", Name, Scene.Name);
// Resume scripts
foreach (SceneObjectGroup sog in m_attachments)
foreach (SceneObjectGroup sog in attachments)
{
sog.RootPart.ParentGroup.CreateScriptInstances(0, false, m_scene.DefaultScriptEngine, GetStateSource());
sog.ResumeScripts();
}
}
}
}
// send the animations of the other presences to me
m_scene.ForEachRootScenePresence(delegate(ScenePresence presence)