具有多处理功能的 Python 代码在 Windows 上不起作用

Question

以下纯初学者代码在 Ubuntu 14.04(Python 2.7.6)和 Cygwin(Python 2.7.8)上 100% 运行良好，但它在 Windows 64 位(Python 2.7.8)上挂起。我在使用 multiprocessing 包的另一个片段中观察到了同样的情况。

from multiprocessing import Process, Queue
from time import time

def WallisPi(N,out):    # Pi by the (slowly convergent) Wallis method.
    prod = 1.0
    for i in xrange(2,N,2):
        prod = prod*(i**2)/((i+1)**2)
    prod = 2.0e0*prod*(i+1)
    out.put(prod)
    return 0

if __name__ == '__main__':
    
    T = [15000000, 25000000, 30000000, 40000000]
    
    ti = time()
    
    q1 = Queue()
    p1 = Process(target=WallisPi, args=(T[0],q1))
    p1.start()
    
    q2 = Queue()
    p2 = Process(target=WallisPi, args=(T[1],q2))
    p2.start()

    q3 = Queue()
    p3 = Process(target=WallisPi, args=(T[2],q3))
    p3.start()

    q4 = Queue()
    p4 = Process(target=WallisPi, args=(T[3],q4))
    p4.start()
    
    p = [p1, p2, p3, p4]
    
    for item in p:
        item.join()

    q = [q1, q2, q3, q4]
    
    print "\n"
    
    Num = len(q)
    
    for i in range(0,Num):
        print "Pi at ",T[i], "terms = ", q[i].get()

    tf = time()
    print "\nElapsed time: ", round((tf-ti),2), " secs."

我想知道这段代码有什么问题吗？

非常感谢您的帮助。

福斯托

Answer 1

根据您运行 Python 的方式，您可能需要使用 freeze_support在 Windows 上:

One needs to call this function straight after the if __name__ == '__main__' line of the main module. For example:

from multiprocessing import Process, freeze_support

def f():
    print 'hello world!'

if __name__ == '__main__':
    freeze_support()
    Process(target=f).start()

另见 programming guidelines on Windows .