Aggiunto un lock.

diff --git a/Dizzy/FileTreeView.cs b/Dizzy/FileTreeView.cs
index fd40fc1..409fd56 100644
--- a/Dizzy/FileTreeView.cs
+++ b/Dizzy/FileTreeView.cs
@@ -45,17 +45,19 @@ namespace Dizzy

 		protected void CellSetup()
 		{
-			// Filename
-			Gtk.CellRendererText filenameRenderer = new Gtk.CellRendererText ();
-			filenameColumn.Resizable = true;
-			filenameColumn.PackStart (filenameRenderer, true);
-			filenameColumn.AddAttribute (filenameRenderer, "text", 0);
-
-			// Utente
-			Gtk.CellRendererText userRenderer = new Gtk.CellRendererText ();
-			userColumn.Resizable = true;
-			userColumn.PackStart (userRenderer, true);
-			userColumn.AddAttribute (userRenderer, "text", 1);
+			lock (this) {
+				// Filename
+				Gtk.CellRendererText filenameRenderer = new Gtk.CellRendererText ();
+				filenameColumn.Resizable = true;
+				filenameColumn.PackStart (filenameRenderer, true);
+				filenameColumn.AddAttribute (filenameRenderer, "text", 0);
+
+				// Utente
+				Gtk.CellRendererText userRenderer = new Gtk.CellRendererText ();
+				userColumn.Resizable = true;
+				userColumn.PackStart (userRenderer, true);
+				userColumn.AddAttribute (userRenderer, "text", 1);
+			}
 		}

 		public void AddFile(Dizzy.File file)