[Docking] Fix a case where a widget could be parented twice

The DockItem widgets can be parented into a floating window, the DockFrame's
DockContainer, or an AutoHideDock. In the latter two cases, it's possible
that a race could cause the widget to be added to its new parent before it's
removed from its old parent.

May fix bug 1445 - MD crashes with SIGABRT occasionally when stopping debugging

4 files changed, 37 insertions, 6 deletions

diff --git a/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/AutoHideBox.cs b/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/AutoHideBox.cs
index 0670fe8f81..78bda70723 100644
--- a/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/AutoHideBox.cs
+++ b/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/AutoHideBox.cs
@@ -104,6 +104,10 @@ namespace MonoDevelop.Components.Docking
 			scrollable.ScrollMode = false;
 			scrollable.Show ();
 
+			if (item.Widget.Parent != null) {
+				((Gtk.Container)item.Widget.Parent).Remove (item.Widget);
+			}
+
 			item.Widget.Show ();
 			scrollable.Add (item.Widget);
 			fr.PackStart (scrollable, true, true, 0);
diff --git a/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/DockContainer.cs b/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/DockContainer.cs
index ca750a94fe..3eb050fcb2 100644
--- a/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/DockContainer.cs
+++ b/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/DockContainer.cs
@@ -173,6 +173,29 @@ namespace MonoDevelop.Components.Docking
 			return res;
 		}
 
+		protected override void OnAdded (Widget widget)
+		{
+			System.Diagnostics.Debug.Assert (
+				widget.Parent == null,
+				"Widget is already parented on another widget");
+			System.Diagnostics.Debug.Assert (
+				System.Linq.Enumerable.Any (items, item => item.Widget == widget),
+				"Can only add widgets to the container that are in the parent DockFrame's DockItem collection");
+
+			widget.Parent = this;
+		}
+
+		protected override void OnRemoved (Widget widget)
+		{
+			System.Diagnostics.Debug.Assert (
+				widget.Parent != this,
+				"Widget is not parented on this widget");
+			System.Diagnostics.Debug.Assert (
+				System.Linq.Enumerable.Any (items, item => item.Widget == widget),
+				"Can only remove widgets from the container that are in the parent DockFrame's DockItem collection");
+
+			widget.Unparent ();
+		}
 
 		public void RelayoutWidgets ()
 		{
diff --git a/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/DockGroup.cs b/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/DockGroup.cs
index 2dfc4ef7ca..685a6f502b 100644
--- a/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/DockGroup.cs
+++ b/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/DockGroup.cs
@@ -693,8 +693,12 @@ namespace MonoDevelop.Components.Docking
 			foreach (DockObject ob in VisibleObjects) {
 				DockGroupItem it = ob as DockGroupItem;
 				if (it != null) {
-					if (it.Item.Widget.Parent == null)
-						it.Item.Widget.Parent = Frame.Container;
+					if (it.Item.Widget.Parent != Frame.Container) {
+						if (it.Item.Widget.Parent != null) {
+							((Gtk.Container)it.Item.Widget.Parent).Remove (it.Item.Widget);
+						}
+						Frame.Container.Add (it.Item.Widget);
+					}
 					if (!it.Item.Widget.Visible && type != DockGroupType.Tabbed)
 						it.Item.Widget.Show ();
 				}
diff --git a/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/DockItem.cs b/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/DockItem.cs
index 7e9f354389..e8a356cd3c 100644
--- a/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/DockItem.cs
+++ b/main/src/core/MonoDevelop.Ide/MonoDevelop.Components.Docking/DockItem.cs
@@ -365,8 +365,7 @@ namespace MonoDevelop.Components.Docking
 		{
 			ResetBarUndockMode ();
 			if (floatingWindow == null) {
-				if (Widget.Parent is Gtk.Container) {
-					MonoDevelop.Core.LoggingService.LogError ("Unparenting {0} from {1} even though it should already be unparented", Widget, widget.Parent);
+				if (Widget.Parent != null) {
 					((Gtk.Container) Widget.Parent).Remove (Widget);
 				}
 				floatingWindow = new Window (GetWindowTitle ());
@@ -422,8 +421,9 @@ namespace MonoDevelop.Components.Docking
 			ResetMode ();
 			if (widget != null) {
 				widget.Hide (); // Avoids size allocation warning
-				if (widget.Parent is Gtk.Container)
-					widget.Unparent ();
+				if (widget.Parent != null) {
+					((Gtk.Container)widget.Parent).Remove (widget);
+				}
 			}
 			dockBarItem = frame.BarDock (pos, this, size);
 			if (widget != null)