It's quite weird, the documentation says set_start_method "should not be used more than once in the program" twice.

The source code also contains the following line

```
# Type of default context -- underlying context can be set at most once
```

I'm not too familiar with the multiprocessing library but with the force parameter set to True, I don't understand why that can't happen. If there's a specific reason, maybe that should be documented too.