Show the error when broadcast_object_list() was passed list with different length

test_broadcast_object_list.py

# !/usr/bin/env python3

import torch
from torch import distributed as dist

dist.init_process_group(backend="nccl")
torch.cuda.set_device(f"cuda:{dist.get_rank()}")

if dist.get_rank() == 0:
    print("I am rank 0")
    a = torch.LongTensor(data=[864]).to("cuda")
    b = ["From Rank 0"]
else:
    print("I am rank 1")
    a = torch.LongTensor(data=[0]).to("cuda")
    b = []

print(f"before BR Rank{dist.get_rank()}: {b=}")
dist.broadcast_object_list(b, src=0)
print(f"after BR Rank{dist.get_rank()}: {b=}")

print(f"before BR Rank{dist.get_rank()}: {a=}")
dist.broadcast(a, src=0)
print(f"after BR Rank{dist.get_rank()}: {a=}")


## Output
## torchrun --nproc_per_node=2 --master_port=33400 t2.py

# I am rank 1
# I am rank 0
# before BR Rank0: b=['From Rank 0']
# before BR Rank1: b=[]
# after BR Rank0: b=['From Rank 0']
# before BR Rank0: a=tensor([864], device='cuda:0')
# after BR Rank0: a=tensor([864], device='cuda:0')
# after BR Rank1: b=[]
# before BR Rank1: a=tensor([0], device='cuda:1')
# after BR Rank1: a=tensor([26], device='cuda:1')