1. Create a JSF KickStart project.
2.Open inputUserName.jsp
3. Copy 1000 times line

<h1><h:outputText value="#{Message.header}"/></h1>

4. Select these 1000 lines.
5. Delete and Save.
6. Undo by Ctrl+Z.

Editor freezes for several minutes. Debugger shows that most time is spent for method SelectionBar.updateNodes() called by SelectionBar.notifyChanged.

The problem is that when 1000 lines are removed, XML model sends thousands of deferred events about each removed XML node, so that instead of one call to SelectionBar.updateNodes(), there are thousands of them.

I suggest creating UIJob at the first call to SelectionBar.notifyChanged, and ignoring subsequent calls until the job is not done.