NonDaemonicSpawnProcess hangs at exit about returnn HOT 2 CLOSED

So, in _bootstrap, you see that there is an early call to _exit_function, which will terminate all daemon procs, and then join all procs (daemon + non-daemon). This call to _exit_function happens before any of our atexit handlers run. (I'm not sure why they do this early call. The atexit handlers would run in reverse order, thus our atexit handlers would run first, and do proper cleanup of our procs, and then _exit_function would run at some later point, but then it's all fine.) So this will hang, as all the procs are non-daemonic, and they will just continue to run.

from returnn.

Our solution/workaround now: The atexit handler we missed is for our own custom Process class. We just add an extra check in the overwritten join function, whether we are currently exiting (luckily multiprocessing.util.is_exiting() is exactly there for this purpose), and if so, then we directly send a SIGINT, just as our atexit handler would do.

from returnn.