Any update on this issue?
I am experiencing similar problem. Below whole error stack.

(pytorch) C:\Users\dzidu\Documents\Python Scripts\pytorch-cifar-master>python main.py
==> Preparing data..
Files already downloaded and verified
Files already downloaded and verified
==> Building model..

Epoch: 0
==> Preparing data..
Files already downloaded and verified
Files already downloaded and verified
==> Building model..

Epoch: 0
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\spawn.py", line 105, in spawn_main
    exitcode = _main(fd)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\spawn.py", line 114, in _main
    prepare(preparation_data)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\spawn.py", line 225, in prepare
    _fixup_main_from_path(data['init_main_from_path'])
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\spawn.py", line 277, in _fixup_main_from_path
    run_name="__mp_main__")
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\runpy.py", line 263, in run_path
    pkg_name=pkg_name, script_name=fname)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "C:\Users\dzidu\Documents\Python Scripts\pytorch-cifar-master\main.py", line 142, in <module>
    train(epoch)
  File "C:\Users\dzidu\Documents\Python Scripts\pytorch-cifar-master\main.py", line 90, in train
    for batch_idx, (inputs, targets) in enumerate(trainloader):
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\site-packages\torch\utils\data\dataloader.py", line 193, in __iter__
    return _DataLoaderIter(self)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\site-packages\torch\utils\data\dataloader.py", line 469, in __init__
    w.start()
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\process.py", line 105, in start
    self._popen = self._Popen(self)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\context.py", line 223, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\context.py", line 322, in _Popen
    return Popen(process_obj)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\popen_spawn_win32.py", line 33, in __init__
    prep_data = spawn.get_preparation_data(process_obj._name)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\spawn.py", line 143, in get_preparation_data
    _check_not_importing_main()
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\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 "main.py", line 142, in <module>
    train(epoch)
  File "main.py", line 90, in train
    for batch_idx, (inputs, targets) in enumerate(trainloader):
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\site-packages\torch\utils\data\dataloader.py", line 193, in __iter__
    return _DataLoaderIter(self)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\site-packages\torch\utils\data\dataloader.py", line 469, in __init__
    w.start()
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\process.py", line 105, in start
    self._popen = self._Popen(self)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\context.py", line 223, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\context.py", line 322, in _Popen
    return Popen(process_obj)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\popen_spawn_win32.py", line 65, in __init__
    reduction.dump(process_obj, to_child)
  File "C:\Users\dzidu\Anaconda3\envs\pytorch\lib\multiprocessing\reduction.py", line 60, in dump
    ForkingPickler(file, protocol).dump(obj)
BrokenPipeError: [Errno 32] Broken pipe

Thanks for any info.
system info:
Microsoft Windows [Version 10.0.17134.706]
(c) 2018 Microsoft Corporation. All rights reserved.

PyTorch:
>>> torch.cuda.is_available()
True
>>> torch.__version__
'1.1.0'

Thanks for any update on this.