Using Threads to Update UI in Vaadin 14 - vaadin

Question

I created a thread (via a lambda expression) to fetch some data based on user input fields but when I try to click on dropdown menus while it is retrieving data I get the mini progress bar indicator. So is a new thread even being created? What am I doing wrong here?
Button doComputation = new Button("Get Results);
doComputation.addClickListener(event -> {
UI ui = UI.getCurrent();
new Thread(() -> {
// Do some work
ui.access(() -> layout.add(results);
}).start();
});
UPDATE: RESOLVED! Unneccesary ui.access calls were made, which locked up resources. Thank you to all that commented and helped.

Answer 1

The code looks correct to me (apart from the missing end parenthesis after ui.access). Is that the only ui.access call, and is that all you do inside it?
I made this example for reference, and the combo box stays responsive while the background task is running.
#Route
public class ThreadView extends VerticalLayout {
public ThreadView() {
Button runThreadButton = new Button("Start thread", e -> {
UI ui = UI.getCurrent();
new Thread(() -> {
try {
Thread.sleep(5000);
} catch (InterruptedException ex) {
ex.printStackTrace();
}
ui.access(() -> Notification.show("Completed"));
}).start();
});
ComboBox<String> comboBox = new ComboBox<>("Items", "One", "Two", "Three");
add(runThreadButton, comboBox);
}
}

Answer 2

So is a new thread even being created?
You can verify that by adding a System.out.println("Thread started") and checking whether that message is printed, or by running your application in debug mode and setting a breakpoint on the part that you're interested in.
What am I doing wrong here?
The code that you showed looks fine. I would guess there's a problem outside the shown code, namely that you have forgotten that you also need to add the #Push annotation. Without that annotation, the server will have no way of directly sending messages to the client.