Enforce existing 5 action hardcoded undo limit.

This was present in the code but not enforced, which led to a memory leak over time as part properties were changed, whether by viewer, script or another source.
This commit enforces that limit, which will soon become configurable.
Regression test for undo limit added
Should help with http://opensimulator.org/mantis/view.php?id=6279

OpenSim/Region/Framework/Scenes/Scene.cs

@@ -151,7 +151,8 @@ namespace OpenSim.Region.Framework.Scenes
         // TODO: need to figure out how allow client agents but deny
         // root agents when ACL denies access to root agent
         public bool m_strictAccessControl = true;
-        public int MaxUndoCount = 5;
+
+        public int MaxUndoCount { get; set; }
 
         // Using this for RegionReady module to prevent LoginsDisabled from changing under our feet;
         public bool LoginLock = false;
@@ -931,6 +932,9 @@ namespace OpenSim.Region.Framework.Scenes
             WestBorders.Add(westBorder);
             BordersLocked = false;
 
+            // TODO: At some point this should be made configurable.
+            MaxUndoCount = 5;
+
             m_eventManager = new EventManager();
 
             m_permissions = new ScenePermissions(this);

OpenSim/Region/Framework/Scenes/SceneObjectPart.cs

@@ -266,8 +266,8 @@ namespace OpenSim.Region.Framework.Scenes
         private string m_sitAnimation = "SIT";
         private string m_text = String.Empty;
         private string m_touchName = String.Empty;
-        private readonly Stack<UndoState> m_undo = new Stack<UndoState>(5);
+        private readonly List<UndoState> m_undo = new List<UndoState>(5);
-        private readonly Stack<UndoState> m_redo = new Stack<UndoState>(5);
+        private readonly List<UndoState> m_redo = new List<UndoState>(5);
 
         private bool m_passTouches = false;
         private bool m_passCollisions = false;
@@ -3176,7 +3176,7 @@ namespace OpenSim.Region.Framework.Scenes
                         {
                             if (m_undo.Count > 0)
                             {
-                                UndoState last = m_undo.Peek();
+                                UndoState last = m_undo[m_undo.Count - 1];
                                 if (last != null)
                                 {
                                     // TODO: May need to fix for group comparison
@@ -3199,7 +3199,10 @@ namespace OpenSim.Region.Framework.Scenes
                             {
                                 UndoState nUndo = new UndoState(this, forGroup);
     
-                                m_undo.Push(nUndo);
+                                m_undo.Add(nUndo);
+
+                                if (m_undo.Count > ParentGroup.GetSceneMaxUndo())
+                                    m_undo.RemoveAt(0);
     
                                 if (m_redo.Count > 0)
                                     m_redo.Clear();
@@ -3245,10 +3248,9 @@ namespace OpenSim.Region.Framework.Scenes
 
                 if (m_undo.Count > 0)
                 {
-                    UndoState goback = m_undo.Pop();
+                    UndoState goback = m_undo[m_undo.Count - 1];
+                    m_undo.RemoveAt(m_undo.Count - 1);
 
-                    if (goback != null)
-                    {
                     UndoState nUndo = null;
     
                     if (ParentGroup.GetSceneMaxUndo() > 0)
@@ -3259,7 +3261,11 @@ namespace OpenSim.Region.Framework.Scenes
                     goback.PlaybackState(this);
 
                     if (nUndo != null)
-                            m_redo.Push(nUndo);
+                    {
+                        m_redo.Add(nUndo);
+
+                        if (m_redo.Count > ParentGroup.GetSceneMaxUndo())
+                            m_redo.RemoveAt(0);
                     }
                 }
 
@@ -3279,19 +3285,20 @@ namespace OpenSim.Region.Framework.Scenes
 
                 if (m_redo.Count > 0)
                 {
-                    UndoState gofwd = m_redo.Pop();
+                    UndoState gofwd = m_redo[m_redo.Count - 1];
+                    m_redo.RemoveAt(m_redo.Count - 1);
 
-                    if (gofwd != null)
-                    {
                     if (ParentGroup.GetSceneMaxUndo() > 0)
                     {
                         UndoState nUndo = new UndoState(this, gofwd.ForGroup);
 
-                            m_undo.Push(nUndo);
+                        m_undo.Add(nUndo);
+
+                        if (m_undo.Count > ParentGroup.GetSceneMaxUndo())
+                            m_undo.RemoveAt(0);
                     }
 
                     gofwd.PlayfwdState(this);
-                    }
 
 //                m_log.DebugFormat(
 //                    "[SCENE OBJECT PART]: Handled redo request for {0} {1}, stack size now {2}",

OpenSim/Region/Framework/Scenes/Tests/SceneObjectUndoRedoTests.cs

@@ -75,6 +75,33 @@ namespace OpenSim.Region.Framework.Scenes.Tests
             Assert.That(g1.GroupScale, Is.EqualTo(secondSize));
         }
 
+        [Test]
+        public void TestUndoLimit()
+        {
+            TestHelpers.InMethod();
+
+            Vector3 firstSize = new Vector3(2, 3, 4);
+            Vector3 secondSize = new Vector3(5, 6, 7);
+            Vector3 thirdSize = new Vector3(8, 9, 10);
+            Vector3 fourthSize = new Vector3(11, 12, 13);
+
+            Scene scene = new SceneHelpers().SetupScene();
+            scene.MaxUndoCount = 2;
+            SceneObjectGroup g1 = SceneHelpers.AddSceneObject(scene);
+
+            g1.GroupResize(firstSize);
+            g1.GroupResize(secondSize);
+            g1.GroupResize(thirdSize);
+            g1.GroupResize(fourthSize);
+
+            g1.RootPart.Undo();
+            g1.RootPart.Undo();
+            g1.RootPart.Undo();
+
+            Assert.That(g1.RootPart.UndoCount, Is.EqualTo(0));
+            Assert.That(g1.GroupScale, Is.EqualTo(secondSize));
+        }
+
         [Test]
         public void TestUndoBeyondAvailable()
         {