Unhandled exceptions in threads should halt the program

[albertz]

I don't really like that we have threads crashing and that this just stays unnoticed (as it was the case in #1643). Shouldn't we stop the whole program when we get an unhandled exception? For the main thread, this is the case.

Is there an easy way to get this behavior? Also that we maybe have better_exchook installed in all threads?

Basically, we should set sys.excepthook in every thread to our custom handler, which then does:

• call better_exchook
• call _thread.interrupt_main()

There is threading.excepthook (since Python 3.8), is this what we want?

[albertz]

There is threading.excepthook (since Python 3.8), is this what we want?

It sounds like this is what we want. But we need Python 3.8. Currently RETURNN still supports Python 3.7. But I think we should increase this to Python 3.8. See #1326.