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例如：下面的代码运行正常在Ubuntu 14.04为什么子进程在Windows上启动时导入主模块，而不在Linux上？
# some imports
import numpy as np
import glob
import sys
import multiprocessing
import os
# creating some temporary data
tmp_dir = os.path.join('tmp', 'nptest')
if not os.path.exists(tmp_dir):
os.makedirs(tmp_dir)
for i in range(10):
x = np.random.rand(100, 50)
y = np.random.rand(200, 20)
file_path = os.path.join(tmp_dir, '%05d.npz' % i)
np.savez_compressed(file_path, x=x, y=y)
def read_npz(path):
data = dict(np.load(path))
return (data['x'], data['y'])
def parallel_read(files):
pool = multiprocessing.Pool(processes=4)
data_list = pool.map(read_npz, files)
return data_list
files = glob.glob(os.path.join(tmp_dir, '*.npz'))
x = parallel_read(files)
print('done')
，但无法在Windows 7上，与沿行的错误消息：
cmd = get_command_line() + [rhandle]
pool = multiprocessing.Pool(processes=4)
File "C:\Anaconda\lib\multiprocessing\forking.py", line 358, in get_command_line
File "C:\Anaconda\lib\multiprocessing\__init__.py", line 232, in Pool
return Pool(processes, initializer, initargs, maxtasksperchild)
File "C:\Anaconda\lib\multiprocessing\pool.py", line 159, in __init__
is not going to be frozen to produce a Windows executable.''')
RuntimeError:
Attempt to start a new process before the current process
has finished its bootstrapping phase.
This probably means that you are on Windows 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 a Windows executable.
self._repopulate_pool()
File "C:\Anaconda\lib\multiprocessing\pool.py", line 223, in _repopulate_pool
w.start()
File "C:\Anaconda\lib\multiprocessing\process.py", line 130, in start
self._popen = Popen(self)
File "C:\Anaconda\lib\multiprocessing\forking.py", line 258, in __init__
cmd = get_command_line() + [rhandle]
File "C:\Anaconda\lib\multiprocessing\forking.py", line 358, in get_command_line
is not going to be frozen to produce a Windows executable.''')
RuntimeError:
Attempt to start a new process before the current process
has finished its bootstrapping phase.
This probably means that you are on Windows 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 a Windows executable.
从我的理解，从事实上，这源于子进程在Windows上启动时导入主模块，而不在Linux上。通过将x = parallel_read(files)放置在主函数中可以防止Windows上的问题。例如：
if __name__ == '__main__':
x = parallel_read(files)
print('done')
为什么子进程在Windows上启动时导入主模块而不在Linux上？
由于Linux具有'fork'以启动具有当前进程状态的副本的新进程，而Windows没有。 –