多处理:如何在类中定义的函数上使用 Pool.map?

Multiprocessing: How to use Pool.map on a function defined in a class?(多处理:如何在类中定义的函数上使用 Pool.map?)

问题描述

当我运行类似的东西时:

When I run something like:

from multiprocessing import Pool

p = Pool(5)
def f(x):
     return x*x

p.map(f, [1,2,3])

它工作正常.然而，把它作为一个类的函数:

it works fine. However, putting this as a function of a class:

class calculate(object):
    def run(self):
        def f(x):
            return x*x

        p = Pool()
        return p.map(f, [1,2,3])

cl = calculate()
print cl.run()

给我以下错误:

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/sw/lib/python2.6/threading.py", line 532, in __bootstrap_inner
    self.run()
  File "/sw/lib/python2.6/threading.py", line 484, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/sw/lib/python2.6/multiprocessing/pool.py", line 225, in _handle_tasks
    put(task)
PicklingError: Can't pickle <type 'function'>: attribute lookup __builtin__.function failed

我看过 Alex Martelli 的一篇帖子处理了同样的问题，但不够明确.

I've seen a post from Alex Martelli dealing with the same kind of problem, but it wasn't explicit enough.

推荐答案

我也对 pool.map 可以接受的函数类型的限制感到恼火.我写了以下内容来规避这一点.它似乎可以工作，即使是对 parmap 的递归使用.

I also was annoyed by restrictions on what sort of functions pool.map could accept. I wrote the following to circumvent this. It appears to work, even for recursive use of parmap.

from multiprocessing import Process, Pipe
from itertools import izip

def spawn(f):
    def fun(pipe, x):
        pipe.send(f(x))
        pipe.close()
    return fun

def parmap(f, X):
    pipe = [Pipe() for x in X]
    proc = [Process(target=spawn(f), args=(c, x)) for x, (p, c) in izip(X, pipe)]
    [p.start() for p in proc]
    [p.join() for p in proc]
    return [p.recv() for (p, c) in pipe]

if __name__ == '__main__':
    print parmap(lambda x: x**x, range(1, 5))

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