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在windows上运行pytorch时，稍不注意就会遇到freeze_support()的错误。解决这种错误只要把代码放到if name == “main”: 中运行就可以了。就忍不住来深究下这个问题。
这是一个关于windows上多进程实现的恩特。在windows上，子进程会自动import启动它的这个文件，而在import的时候是会自动执行这些语句的。如果不加__main__限制的化，就会无限递归创建子进程，进而报错。于是import的时候使用 name == “main” 保护起来就可以了。
出现错误：
Traceback (most recent call last):File "<string>", line 1, in <module>File "D:\opt\anaconda3\lib\multiprocessing\spawn.py", line 105, in spawn_mainexitcode = _main(fd)File "D:\opt\anaconda3\lib\multiprocessing\spawn.py", line 114, in _mainprepare(preparation_data)File "D:\opt\anaconda3\lib\multiprocessing\spawn.py", line 225, in prepare_fixup_main_from_path(data['init_main_from_path'])File "D:\opt\anaconda3\lib\multiprocessing\spawn.py", line 277, in _fixup_main_from_pathrun_name="__mp_main__")File "D:\opt\anaconda3\lib\runpy.py", line 263, in run_pathpkg_name=pkg_name, script_name=fname)File "D:\opt\anaconda3\lib\runpy.py", line 96, in _run_module_codemod_name, mod_spec, pkg_name, script_name)File "D:\opt\anaconda3\lib\runpy.py", line 85, in _run_codeexec(code, run_globals)File "D:\ML_Study\PyTorch-garbage-classify\garbage-classification-using-pytorch.py", line 59, in <module>image,label = next(iter(train_loader))File "D:\opt\anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 819, in __iter__return _DataLoaderIter(self)File "D:\opt\anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 560, in __init__w.start()File "D:\opt\anaconda3\lib\multiprocessing\process.py", line 105, in startself._popen = self._Popen(self)File "D:\opt\anaconda3\lib\multiprocessing\context.py", line 223, in _Popenreturn _default_context.get_context().Process._Popen(process_obj)File "D:\opt\anaconda3\lib\multiprocessing\context.py", line 322, in _Popenreturn Popen(process_obj)File "D:\opt\anaconda3\lib\multiprocessing\popen_spawn_win32.py", line 33, in __init__prep_data = spawn.get_preparation_data(process_obj._name)File "D:\opt\anaconda3\lib\multiprocessing\spawn.py", line 143, in get_preparation_data_check_not_importing_main()File "D:\opt\anaconda3\lib\multiprocessing\spawn.py", line 136, in _check_not_importing_mainis not going to be frozen to produce an executable.''')
RuntimeError: An attempt has been made to start a new process before thecurrent process has finished its bootstrapping phase.This probably means that you are not using fork to start yourchild processes and you have forgotten to use the proper idiomin the main module:if __name__ == '__main__':freeze_support()...The "freeze_support()" line can be omitted if the programis not going to be frozen to produce an executable.
解决方案：
if __name__ == '__main__':# 代码
通过上述方式实验完美解决，这里说下我的实验版本
In [1]: import torch
In [2]: import torchvision
In [3]: torch.version
Out[3]: ‘1.0.1’
In [4]: torchvision.version
Out[4]: ‘0.2.2’
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