I’m running Distributed Data Parallel example 3 in jupyter labs, and getting an error:
process 1 terminated with exit code 1

How can I fix it? Where should I look at? I tried using “nccl” or “mpi” in dist.init_process_group, no effect. Replacing the entire body of example() with pass: no effect.
Full stack trace:
---------------------------------------------------------------------------
Exception                                 Traceback (most recent call last)
<ipython-input-29-703537cd0120> in <module>
     33         join=True)
     34 
---> 35 main()

<ipython-input-29-703537cd0120> in main()
     28 def main():
     29     world_size = 2
---> 30     mp.spawn(example,
     31         args=(world_size,),
     32         nprocs=world_size,

/usr/local/lib/python3.8/site-packages/torch/multiprocessing/spawn.py in spawn(fn, args, nprocs, join, daemon, start_method)
    197                ' torch.multiprocessing.start_process(...)' % start_method)
    198         warnings.warn(msg)
--> 199     return start_processes(fn, args, nprocs, join, daemon, start_method='spawn')

/usr/local/lib/python3.8/site-packages/torch/multiprocessing/spawn.py in start_processes(fn, args, nprocs, join, daemon, start_method)
    155 
    156     # Loop on join until it returns True or raises an exception.
--> 157     while not context.join():
    158         pass
    159 

/usr/local/lib/python3.8/site-packages/torch/multiprocessing/spawn.py in join(self, timeout)
    108                 )
    109             else:
--> 110                 raise Exception(
    111                     "process %d terminated with exit code %d" %
    112                     (error_index, exitcode)

Exception: process 1 terminated with exit code 1