Pytorch报错：“freeze_support()“ line can be omitted if the program is not going to be frozen（已解决）

报错提示：

运行 pytoch 测试代码时，出现如下报错：

model [TestModel] was created
liu yaxin 21
Traceback (most recent call last):
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "test.py", line 50, in <module>
for i, data in enumerate(dataset):
File "C:\ProgramData\Anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 291, in __iter__
File "C:\ProgramData\Anaconda3\lib\multiprocessing\spawn.py", line 105, in spawn_main
return _MultiProcessingDataLoaderIter(self)
File "C:\ProgramData\Anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 737, in __init__
exitcode = _main(fd)
File "C:\ProgramData\Anaconda3\lib\multiprocessing\spawn.py", line 114, in _main
prepare(preparation_data)w.start()

File "C:\ProgramData\Anaconda3\lib\multiprocessing\spawn.py", line 225, in prepare
File "C:\ProgramData\Anaconda3\lib\multiprocessing\process.py", line 105, in start
self._popen = self._Popen(self)_fixup_main_from_path(data['init_main_from_path'])

File "C:\ProgramData\Anaconda3\lib\multiprocessing\context.py", line 223, in _Popen
File "C:\ProgramData\Anaconda3\lib\multiprocessing\spawn.py", line 277, in _fixup_main_from_path
return _default_context.get_context().Process._Popen(process_obj)run_name="__mp_main__")

File "C:\ProgramData\Anaconda3\lib\multiprocessing\context.py", line 322, in _Popen
File "C:\ProgramData\Anaconda3\lib\runpy.py", line 263, in run_path
return Popen(process_obj)
pkg_name=pkg_name, script_name=fname) File "C:\ProgramData\Anaconda3\lib\multiprocessing\popen_spawn_win32.py", line 65, in __init__

File "C:\ProgramData\Anaconda3\lib\runpy.py", line 96, in _run_module_code
reduction.dump(process_obj, to_child)
File "C:\ProgramData\Anaconda3\lib\multiprocessing\reduction.py", line 60, in dump
mod_name, mod_spec, pkg_name, script_name)
File "C:\ProgramData\Anaconda3\lib\runpy.py", line 85, in _run_code
ForkingPickler(file, protocol).dump(obj)
BrokenPipeError : exec(code, run_globals)[Errno 32] Broken pipe

File "E:\Code\semi-dehazing-master\test.py", line 50, in <module>
for i, data in enumerate(dataset):
File "C:\ProgramData\Anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 291, in __iter__
return _MultiProcessingDataLoaderIter(self)
File "C:\ProgramData\Anaconda3\lib\site-packages\torch\utils\data\dataloader.py", line 737, in __init__
w.start()
File "C:\ProgramData\Anaconda3\lib\multiprocessing\process.py", line 105, in start
self._popen = self._Popen(self)
File "C:\ProgramData\Anaconda3\lib\multiprocessing\context.py", line 223, in _Popen
return _default_context.get_context().Process._Popen(process_obj)
File "C:\ProgramData\Anaconda3\lib\multiprocessing\context.py", line 322, in _Popen
return Popen(process_obj)
File "C:\ProgramData\Anaconda3\lib\multiprocessing\popen_spawn_win32.py", line 33, in __init__
prep_data = spawn.get_preparation_data(process_obj._name)
File "C:\ProgramData\Anaconda3\lib\multiprocessing\spawn.py", line 143, in get_preparation_data
_check_not_importing_main()
File "C:\ProgramData\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.

先看解决方案：

在代码前面加一句：

if __name__ == '__main__':
    xxxxx # Your code

我的例子如下：

if __name__ == '__main__':
    with torch.no_grad():
        for i, data in enumerate(dataset):
            if i >= opt.how_many:
                break
            counter = i
            model.set_input(data)
            model.test()
            visuals = model.get_current_visuals()
            PSNR_b = PSNR(visuals['real_A'], visuals['real_B'])
            PSNR_d = PSNR(visuals['fake_B'], visuals['real_B'])
            avgPSNR += PSNR_d
            avgPSNR_b += PSNR_b
            # .......

进一步探究：

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。【原文链接：https://blog.csdn.net/shenfuli/article/details/103969964】

Pytorch报错：“freeze_support()“ line can be omitted if the program is not going to be frozen（已解决）

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