错误：

Traceback (most recent call last):

File "", line 1, in File "C:\Program Files\Anaconda3\lib\multiprocessing\spawn.py", line 106, in spawn_main

exitcode = _main(fd)

File "C:\Program Files\Anaconda3\lib\multiprocessing\spawn.py", line 115, in _main

prepare(preparation_data)

File "C:\Program Files\Anaconda3\lib\multiprocessing\spawn.py", line 226, in prepare

_fixup_main_from_path(data['init_main_from_path'])

File "C:\Program Files\Anaconda3\lib\multiprocessing\spawn.py", line 278, in _fixup_main_from_path

run_name="__mp_main__")

File "C:\Program Files\Anaconda3\lib\runpy.py", line 254, in run_path

pkg_name=pkg_name, script_name=fname)

File "C:\Program Files\Anaconda3\lib\runpy.py", line 96, in _run_module_code

mod_name, mod_spec, pkg_name, script_name)

File "C:\Program Files\Anaconda3\lib\runpy.py", line 85, in _run_code

exec(code, run_globals)

File "D:\pycharm\python_accelerate\pkg_acc.py", line 121, in pool = multiprocessing.Pool(processes=3)

File "C:\Program Files\Anaconda3\lib\multiprocessing\context.py", line 118, in Pool

context=self.get_context())

File "C:\Program Files\Anaconda3\lib\multiprocessing\pool.py", line 168, in __init__

self._repopulate_pool()

File "C:\Program Files\Anaconda3\lib\multiprocessing\pool.py", line 233, in _repopulate_pool

w.start()

File "C:\Program Files\Anaconda3\lib\multiprocessing\process.py", line 105, in start

self._popen = self._Popen(self)

File "C:\Program Files\Anaconda3\lib\multiprocessing\context.py", line 313, in _Popen

return Popen(process_obj)

File "C:\Program Files\Anaconda3\lib\multiprocessing\popen_spawn_win32.py", line 34, in __init__

prep_data = spawn.get_preparation_data(process_obj._name)

File "C:\Program Files\Anaconda3\lib\multiprocessing\spawn.py", line 144, in get_preparation_data

_check_not_importing_main()

File "C:\Program Files\Anaconda3\lib\multiprocessing\spawn.py", line 137, 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.

代码：

def muchjob(x):

time.sleep(2)

return x**2

tic = time.time()

import time

ans = [muchjob(i) for i in range(4)]

print('ans', ans)

toc = time.time()

print('used {:.10}s'.format(toc - tic))

print('*' * 20)

tic = time.time()

import multiprocessing

pool = multiprocessing.Pool(processes=3)

res = []

for i in range(4):

res.append(pool.apply_async(muchjob, (i,)))

pool.close()

pool.join()

ans = [r.get() for r in res]

print('ans', ans)

toc = time.time()

print('used {:.10}s'.format(toc-tic))

这是由于mutiprocessing要写在main下，修改如下：

def muchjob(x):

time.sleep(2)

return x**2

if __name__ == '__main__':

tic = time.time()

import time

ans = [muchjob(i) for i in range(4)]

print('ans', ans)

toc = time.time()

print('used {:.10}s'.format(toc - tic))

print('*' * 20)

tic = time.time()

import multiprocessing

pool = multiprocessing.Pool(processes=3)

res = []

for i in range(4):

res.append(pool.apply_async(muchjob, (i,)))

pool.close()

pool.join()

ans = [r.get() for r in res]

print('ans', ans)

toc = time.time()

print('used {:.10}s'.format(toc-tic))

reference：

https://blog.csdn.net/jacke121/article/details/79826420

https://stackoverflow.com/questions/29690091/python2-7-exception-the-freeze-support-line-can-be-omitted-if-the-program