Background thread, async and GUI (dlangui)

[Bagomot]

On Friday, 8 July 2022 at 08:04:45 UTC, Bagomot wrote:
> On Thursday, 7 July 2022 at 18:26:15 UTC, Ali Çehreli wrote:
>
> Summing up your help and GrimMaple, I understood how to make 
> the file download progress bar beautifully. Thank you!
>
> I only have a question with how I can work with the GUI from 
> other threads. For example, in my application I have a button 
> (GUI) that starts a long running job. As I understand it, it 
> should run it in a separate thread so as not to block the GUI.
>
> I did it through Thread, but now I realized that there are more 
> convenient ways through Task.
>
> But I do not understand how I can manage the GUI from that 
> separate task. For example, I start the task with the button 
> and block the button press (without blocking the entire GUI), 
> it does its job and unblocks the button.
>
> This is where help is needed. How is it fundamentally correct 
> to do this in D, and how to do it in general with dlangui?

Let's even look at the example of downloading a file.

Here in my application I have a button and its click event. I can 
set it to work on click. But I do not know how to do it so that 
the GUI does not block for the duration of the work. I do as in 
Ali's example, but the GUI is still blocked:
```d
auto btn = new Button("Run"d);
btn.click = delegate(Widget src) {
     auto request = Request("dlang.org");
     auto downloadTask = task!download(&request);
     downloadTask.executeInNewThread;
     return true;
};
```
How to do it right? Not only for downloading, but for any 
background work in dlangui? Maybe someone knows?