This is a fundamental misunderstanding of how GUIs must necessarily work. There should be no possibility of race conditions if you understand the threading model.

The visual representation updating (greying out button) is a result of disabling the button, not the same thing. In virtually every GUI toolkit I've ever used there is the concept of the main UI thread, and everything that happens (input and display updates) necessarily has to go through that single thread in order to ensure correctness. (This applies to browsers, too.) That's why input goes into a queue, so you can easily do things like:

(All on the main UI thread):

  - Receive click event 1: disable button, start background process. Possibly redraw button UI *but it doesn't matter because the UI display is not the state, it's just a view*.

  - Receive click event 2: nothing happens, button is disabled

  - Background process finishes, posts update to re-enable the button

  - Receive click event 3: disable button, start background process, etc.

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