In this case, can I modify swing GUI out of swing thread?

Question

I know the Swing single thread rule and design (Swing is not thread safe).
For time-consuming task, we are using other thread to do the task and
we use SwingUtilities.invokeAndWait() or SwingUtilities.invokeLater (or SwingWorker) to update Swing GUI.
My problem is, my time-consuming task is related to Swing GUI stuff
(like set expanded state of a huge tree, walk through entire tree... etc), not the classic DB task.
So my time-consuming Swing task must executed on Swing thread, but it will block the GUI responsivity.
I solve this problem by show up a modal waiting dialog to ask user to wait and
also allow user to cancel the task.
Then I create an other thread (no event-dispatch thread) to do my Swing time-consuming tasks.
Since the modal dialog (do nothing just allow user to cancel) is a thread spawn by
Swing event-dispatch thread and block the Swing dispatch-thread until dialog close.
So my thread can modify Swing GUI stuff safely since there are no any concurrent access problem.
In this case, I broke the Swing's suggestion, modify Swing stuff out of Swing event-dispatch thread.
But as I said, there are no concurrent access, so I am safe.
Am I right? Are you agree? Do you have other better idea?
Thanks for your help.

Answer 1

If you drag your modal dialog around in front of the background UI, then there is concurrent access: paint requests in your main window as the foreground window moves around.