沒有“if __name__ =='__ main__'的python3.x多處理循環：”

Question

我有這個文件（它沒有任何有用的工作，它只用於學習）：

import multiprocessing,sys
def parent(numproc=2):
    print ('at start')
    childs=[]
    print ('bfore Pipe')
    (parentEnd,childEnd)=multiprocessing.Pipe()
    i=0
    print ('printing i:',i)
    child=multiprocessing.Process(target=child_proc, args=(childEnd,i))
    print ('created child')
    child.start()
    print ('started child')
    print ('joining child')
    child.join()
    print ('joined child')
    print ('exeted from for i in childs')
    mins=[1,2]
    print ('task ended. result: ',min(mins))
def child_proc(pipe,name):
    pass
if __name__ == '__main__':
    parent()

以這種形式運行完美：

at start
bfore Pipe
printing i: 0
created child
started child
joining child
joined child
exeted from for i in childs
task ended. result:  1

但如果我放入文件的末尾而不是

if __name__ == '__main__':
    parent()

只要

parent()

它落在周期......

at start
bfore Pipe
printing i: 0
created child
started child
joining child
at start
bfore Pipe
printing i: 0
created child
started child
joining child
at start
bfore Pipe
printing i: 0
created child
started child
joining child
Traceback (most recent call last):

為什么？！ 這個if條款有什么不同？

Answer 1

這是MS Windows上的multiprocessing問題：主模塊由子任務導入，因此任何代碼都不受if __name__ . . .保護if __name__ . . . if __name__ . . . 子句再次運行，導致無限循環。

Answer 2

子進程具有以下__name__ ： __parents_main__而不是__main__了。 這就是為什么在__name__變量時，您的進程不會循環。

有關這方面的更多信息，請參閱安全導入主模塊一章