I'm not sure that it's not implemented yet, I hope that it is. But I know that in .Net programmers should manually run time-consuming task in the background thread.

So every time we handle some UI event and we understand that this will take some time we also understand that this will hang UI thread and our application. And then we make all this Background work things and handle callbacks or whatever.

So my question is:

Is there in some language/platform a mechanism that will automatically run time-consuming tasks in the background and will do all related work itself? So we just write the code for handling specific UI event and this code will be somehow detected as time-consuming and will be executed in background.

And if there isn't, then why?