* Change Util.FireAndForget to use ThreadPool.UnsafeQueueUserWorkItem(). This avoids .NET remoting and a managed->unmanaged->managed jump. Overall, a night and day performance difference

* Initialize the LLClientView prim full update queue to the number of prims in the scene for a big performance boost
* Reordered some comparisons on hot code paths for a minor speed boost
* Removed an unnecessary call to the expensive DateTime.Now function (if you *have* to get the current time as opposed to Environment.TickCount, always use DateTime.UtcNow)
* Don't fire the queue empty callback for the Resend category
* Run the outgoing packet handler thread loop for each client synchronously. It seems like more time was being spent doing the execution asynchronously, and it made deadlocks very difficult to track down
* Rewrote some expensive math in LandObject.cs
* Optimized EntityManager to only lock on operations that need locking, and use TryGetValue() where possible
* Only update the attachment database when an object is attached or detached
* Other small misc. performance improvements

OpenSim/Region/ClientStack/LindenUDP/LLUDPClient.cs

@@ -506,8 +506,13 @@ namespace OpenSim.Region.ClientStack.LindenUDP
         /// for</param>
         private void BeginFireQueueEmpty(int throttleIndex)
         {
-            if (!m_onQueueEmptyRunning[throttleIndex])
-                Util.FireAndForget(FireQueueEmpty, throttleIndex);
+            // Unknown is -1 and Resend is 0. Make sure we are only firing the 
+            // callback for categories other than those
+            if (throttleIndex > 0)
+            {
+                if (!m_onQueueEmptyRunning[throttleIndex])
+                    Util.FireAndForget(FireQueueEmpty, throttleIndex);
+            }
         }
 
         /// <summary>