文件句柄为父进程打开，但对每个子进程关闭

Question

我写了这个小例子：

import multiprocessing
from functools import partial
def foo(x, fp):
    print str(x) + " "+ str(fp.closed)
    return
def main():
    with open("test.txt", 'r') as file:
        pool = multiprocessing.Pool(multiprocessing.cpu_count())
        partial_foo = partial(foo, fp=file)
        print file.closed
        pool.map(partial_foo, [1,2,3,4])
        pool.close()
        pool.join()
        print file.closed
        print "done"
if __name__=='__main__':
    main()

这将打印：

False
2 True
3 True 
1 True
4 True
False
done

我的问题是为什么关闭子进程的文件句柄，以及如何使它们保持打开状态，以便每个进程都可以处理该文件？

由于在评论中被问到：

$ uname -a && python2.7 -V
Linux X220 3.17.6-1-ARCH #1 SMP PREEMPT Sun Dec 7 23:43:32 UTC 2014 x86_64 GNU/Linux
Python 2.7.9

Answer 1

它与将文件作为参数传递有关。将 fp 更改为文件

import multiprocessing
from functools import partial
def foo(x, fp):
    print str(x) + " "+ str(file.closed)
    return
if __name__=='__main__':
    with open("test.txt", 'r') as file:
        pool = multiprocessing.Pool(multiprocessing.cpu_count())
        partial_foo = partial(foo, fp=file)
        print file.closed
        pool.map(partial_foo, [1,2,3,4])
        pool.close()
        pool.join()
        print file.closed
        print "done"

输出

False
1 False
2 False
3 False
4 False
False
done