Hello everyone,
I am trying to train an Unet model using DDP, the dataset is a map-style dataset & is stored in pickle files. If I set the number of data loader workers to more than 0 it fails with the below error, even if I use a single GPU. Is there is anything that I should take into account while working with pickle files under DDP?
-- Process 0 terminated with the following error:
Traceback (most recent call last):
File "/home/user1/.local/lib/python3.8/site-packages/torch/multiprocessing/spawn.py", line 59, in _wrap
fn(i, *args)
File "/home/user1/training_functions.py", line 469, in train_net_ddp
eval_net(model=model, classes=classes, criterion=focal_criterion, val_loader=val_dataloader, cuda=cuda, device=index, writer=None,
File "/home/user1/.local/lib/python3.8/site-packages/torch/autograd/grad_mode.py", line 28, in decorate_context
return func(*args, **kwargs)
File "/home/user1/training_functions.py", line 146, in eval_net
for idx, data in enumerate(val_loader):
File "/home/user1/.local/lib/python3.8/site-packages/torch/utils/data/dataloader.py", line 359, in __iter__
return self._get_iterator()
File "/home/user1/.local/lib/python3.8/site-packages/torch/utils/data/dataloader.py", line 305, in _get_iterator
return _MultiProcessingDataLoaderIter(self)
File "/home/user1/.local/lib/python3.8/site-packages/torch/utils/data/dataloader.py", line 918, in __init__
w.start()
File "/home/user1/anaconda3/envs/bttenv/lib/python3.8/multiprocessing/process.py", line 121, in start
self._popen = self._Popen(self)
File "/home/user1/anaconda3/envs/bttenv/lib/python3.8/multiprocessing/context.py", line 224, in _Popen
return _default_context.get_context().Process._Popen(process_obj)
File "/home/user1/anaconda3/envs/bttenv/lib/python3.8/multiprocessing/context.py", line 284, in _Popen
return Popen(process_obj)
File "/home/user1/anaconda3/envs/bttenv/lib/python3.8/multiprocessing/popen_spawn_posix.py", line 32, in __init__
super().__init__(process_obj)
File "/home/user1/anaconda3/envs/bttenv/lib/python3.8/multiprocessing/popen_fork.py", line 19, in __init__
self._launch(process_obj)
File "/home/user1/anaconda3/envs/bttenv/lib/python3.8/multiprocessing/popen_spawn_posix.py", line 47, in _launch
reduction.dump(process_obj, fp)
File "/home/user1/anaconda3/envs/bttenv/lib/python3.8/multiprocessing/reduction.py", line 60, in dump
ForkingPickler(file, protocol).dump(obj)
AttributeError: Can't pickle local object 'get_dataloaders_generated_data.<locals>.dataset'