On Windows 10, ValueError: cannot find context for 'fork'

[witignite]

When I tried to run visualise_data.ipynb on Windows, I received the following error:

D:\l5kit\l5kit\l5kit\dataset\select_agents.py in <module>
     20 from l5kit.geometry import angular_distance
     21 
---> 22 multiprocessing.set_start_method("fork", force=True)  # this fix loop in python 3.8 on MacOS
     23 os.environ["BLOSC_NOLOCK"] = "1"  # this is required for multiprocessing
     24 

~\Anaconda3\envs\py37\lib\multiprocessing\context.py in set_start_method(self, method, force)
    244             self._actual_context = None
    245             return
--> 246         self._actual_context = self.get_context(method)
    247 
    248     def get_start_method(self, allow_none=False):

~\Anaconda3\envs\py37\lib\multiprocessing\context.py in get_context(self, method)
    236             return self._actual_context
    237         else:
--> 238             return super().get_context(method)
    239 
    240     def set_start_method(self, method, force=False):

~\Anaconda3\envs\py37\lib\multiprocessing\context.py in get_context(self, method)
    190             ctx = _concrete_contexts[method]
    191         except KeyError:
--> 192             raise ValueError('cannot find context for %r' % method) from None
    193         ctx._check_available()
    194         return ctx

ValueError: cannot find context for 'fork'

[HiddenBeginner]

I temporarily fixed the problem by modifying the script

multiprocessing.set_start_method("fork", force=True)

in l5kit.dataset.select_agents.py to

multiprocessing.set_start_method("spawn", force=True)

Please note that it may not be the right solution.

[lucabergamini]

Hey, we are aware of the issue. I've started #124 to ensure fork is only used on macOS (it was causing a deadlock there on python 3.8)

[lucabergamini]

#124 has been merged and should fix this. I'm closing this for now but feel free to reopen it