Python multiprocessing.Pool在Windows上很奇怪

Question

我有一个超简单的python脚本，如这里定义

import multiprocessing
from multiprocessing import Pool

print "CPUs: " + str(multiprocessing.cpu_count())
convertPool = Pool(multiprocessing.cpu_count())

在Linux上，这似乎与我预期的一样，程序只是启动，然后打印出内核数量，然后退出。 但是，在Windows上，该程序将继续调用新的python命令并打印出“ CPU：4”（我有4个内核），并且永不停止运行，最终将杀死该计算机。 有人可以解释一下这是怎么回事吗？

谢谢

编辑：我现在有以下程序仍然无法正常运行

import sys
import os
import subprocess
from subprocess import Popen, PIPE
from threading import Thread
import multiprocessing
from multiprocessing import Pool, freeze_support

try:
    from Queue import Queue, Empty
except ImportError:
    from queue import Queue, Empty  # python 3.x

ON_POSIX = "posix" in sys.builtin_module_names

def myPrint(line, logWriter):
    if logWriter is None:
        # This will print without a newline, cause the process
        # has its own newlines
        sys.stdout.write(line)
    else:
        logWriter.write(line.strip())
        logWriter.write("\n")
        logWriter.flush()

# This is gotten from http://stackoverflow.com/questions/375427/non-blocking-read-on-a-subprocess-pipe-in-python
def executeCommand(cmd, logWriter):
   myPrint(cmd + "\n", logWriter)
    p = Popen(cmd, stdout=PIPE, bufsize=4096, close_fds=ON_POSIX, shell=True)
    q = Queue()
    t = Thread(target=enqueue_output, args=(p.stdout, q))
    t.daemon = True # thread dies with the program
    t.start()

    # read line without blocking
    while t.isAlive() or not q.empty():
        try:
            line = q.get_nowait() # or q.get(timeout=.1)
        except Empty:
            pass # Do nothing
        else: # If there is a line, then print it 
            if logWriter is not None:
                myPrint(line, logWriter)
        # Sleep to prevent python from using too much cpu
        time.sleep(0.05)

if __name__ == "__main__":
    freeze_support()
    convertPool = Pool(multiprocessing.cpu_count())
    # Now let's smooth and threshold all the masks
    for foo in bar:
        threshSmoothCmd = "ConvertImage.exe -i " + foo + " -o " + foo
        myPrint(threshSmoothCmd + "\n", None)
        convertPool.apply_async(executeCommand,(threshSmoothCmd, None,))

    convertPool.close()
    convertPool.join()
print "Finished processing"

ConvertImage.exe是我自己写的可执行文件foo和bar只是占位符。 在Linux上，这将启动multiprocessing.cpu_count（）个ConvertImage.exe进程的数量，然后在所有ConvertImage.exe进程完成后打印“ Finished”处理。 在Windows上，这立即启动len（bar）ConvertImage.exe进程，然后立即打印Finished处理并退出。 如何使Windows版本的行为与Linux版本类似？

Answer 1

我发现了这一点，它工作正常，由于忘记了一些导入操作，导致示例程序张贴错误，并导致了所描述的行为。 在所有导入都正确之后，此示例在Windows和Linux上运行良好。