I’m using torch version 1.8.1+cu102
It will raise “RuntimeError: DataLoader worker exited unexpectedly” when num_workers in DataLoader is not 0.
This is the minimum code that produced error:
from torch.utils.data import DataLoader
trainloader = DataLoader((1,2,3,4,5),num_workers=1)
for data in trainloader:
print(data)
if I change num_workers to 0, this code prints tensor(1), tensor(2),…, tensor(5) as expected, but when I set it to nonzero, it results this error:
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "C:\Users\Sam\anaconda3\lib\multiprocessing\spawn.py", line 105, in spawn_main
exitcode = _main(fd)
File "C:\Users\Sam\anaconda3\lib\multiprocessing\spawn.py", line 114, in _main
prepare(preparation_data)
File "C:\Users\Sam\anaconda3\lib\multiprocessing\spawn.py", line 225, in prepare
_fixup_main_from_path(data['init_main_from_path'])
File "C:\Users\Sam\anaconda3\lib\multiprocessing\spawn.py", line 277, in _fixup_main_from_path
run_name="__mp_main__")
File "C:\Users\Sam\anaconda3\lib\runpy.py", line 263, in run_path
pkg_name=pkg_name, script_name=fname)
File "C:\Users\Sam\anaconda3\lib\runpy.py", line 96, in _run_module_code
mod_name, mod_spec, pkg_name, script_name)
File "C:\Users\Sam\anaconda3\lib\runpy.py", line 85, in _run_code
exec(code, run_globals)
File "C:\Users\Sam\Desktop\PyTortto\examples\CNN_tiny.py", line 5, in <module>
for data in trainloader:
File "C:\Users\Sam\anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 355, in __iter__
return self._get_iterator()
File "C:\Users\Sam\anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 301, in _get_iterator
return _MultiProcessingDataLoaderIter(self)
File "C:\Users\Sam\anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 914, in __init__
w.start()
File "C:\Users\Sam\anaconda3\lib\multiprocessing\process.py", line 112, in start
self._popen = self._Popen(self)
File "C:\Users\Sam\anaconda3\lib\multiprocessing\context.py", line 223, in _Popen
return _default_context.get_context().Process._Popen(process_obj)
File "C:\Users\Sam\anaconda3\lib\multiprocessing\context.py", line 322, in _Popen
return Popen(process_obj)
File "C:\Users\Sam\anaconda3\lib\multiprocessing\popen_spawn_win32.py", line 46, in __init__
prep_data = spawn.get_preparation_data(process_obj._name)
File "C:\Users\Sam\anaconda3\lib\multiprocessing\spawn.py", line 143, in get_preparation_data
_check_not_importing_main()
File "C:\Users\Sam\anaconda3\lib\multiprocessing\spawn.py", line 136, in _check_not_importing_main
is not going to be frozen to produce an executable.''')
RuntimeError:
An attempt has been made to start a new process before the
current process has finished its bootstrapping phase.
This probably means that you are not using fork to start your
child processes and you have forgotten to use the proper idiom
in the main module:
if __name__ == '__main__':
freeze_support()
...
The "freeze_support()" line can be omitted if the program
is not going to be frozen to produce an executable.
Traceback (most recent call last):
File "C:\Users\Sam\anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 986, in _try_get_data
data = self._data_queue.get(timeout=timeout)
File "C:\Users\Sam\anaconda3\lib\multiprocessing\queues.py", line 105, in get
raise Empty
_queue.Empty
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "C:/Users/Sam/Desktop/PyTortto/examples/CNN_tiny.py", line 5, in <module>
for data in trainloader:
File "C:\Users\Sam\anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 517, in __next__
data = self._next_data()
File "C:\Users\Sam\anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 1182, in _next_data
idx, data = self._get_data()
File "C:\Users\Sam\anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 1148, in _get_data
success, data = self._try_get_data()
File "C:\Users\Sam\anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 999, in _try_get_data
raise RuntimeError('DataLoader worker (pid(s) {}) exited unexpectedly'.format(pids_str)) from e
RuntimeError: DataLoader worker (pid(s) 9980) exited unexpectedly
Process finished with exit code 1
Thanks for any advice!