python进程池multiprocessing.Pool运行错误：The freeze_support() line can be omitted if the program is not g

import multiprocessing
import time

def func(msg):
print(‘msg: ‘, msg)
time.sleep(1)
print(’----’)

pool = multiprocessing.Pool(processes=4)
for i in range(10):
msg = ‘hello world %d’ % i
pool.apply_async(func, (msg, ))

pool.close()
pool.join()
上面的代码运行将产生如下错误信息：
RuntimeError:
An attempt has been made to start a new process before the
current process has finished its .

    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.
  
    **

从错误信息可以看出进程池相关代码应该放在if name == 'main’下面，代码修改如下：

import multiprocessing
import time

def func(msg):
print(‘msg: ‘, msg)
time.sleep(1)
print(’----’)

if name == ‘main’:
pool = multiprocessing.Pool(processes=4)
for i in range(10):
msg = ‘hello world %d’ % i
pool.apply_async(func, (msg, ))

pool.close()
pool.join()