Eu estou tentando calcular e gerar gráficos usando multiprocessamento. No Linux, o código abaixo é executado corretamente, no entanto, no Mac (ML) não, dando o erro abaixo:

import multiprocessing
import matplotlib.pyplot as plt
import numpy as np
import rpy2.robjects as robjects

def main():
    pool = multiprocessing.Pool()
    num_figs = 2
    # generate some random numbers
    input = zip(np.random.randint(10,1000,num_figs), 
                range(num_figs))

    pool.map(plot, input)

def plot(args):
    num, i = args
    fig = plt.figure()
    data = np.random.randn(num).cumsum()
    plt.plot(data)

main()

O Rpy2 é rpy2 == 2.3.1 e R é 2.13.2 (eu não pude instalar a versão mais recente do R 3.0 e rpy2 em qualquer mac sem ter uma falha de segmentação).

O erro é:

The process has forked and you cannot use this CoreFoundation functionality safely. You MUST exec().
Break on __THE_PROCESS_HAS_FORKED_AND_YOU_CANNOT_USE_THIS_COREFOUNDATION_FUNCTIONALITY___YOU_MUST_EXEC__() to debug.
The process has forked and you cannot use this CoreFoundation functionality safely. You MUST exec().

Eu tentei de tudo para entender qual é o problema sem sorte. Minha configuração é:

Danials-MacBook-Pro:~ danialt$ brew --config
HOMEBREW_VERSION: 0.9.4
ORIGIN: https://github.com/mxcl/homebrew
HEAD: 705b5e133d8334cae66710fac1c14ed8f8713d6b
HOMEBREW_PREFIX: /usr/local
HOMEBREW_CELLAR: /usr/local/Cellar
CPU: dual-core 64-bit penryn
OS X: 10.8.3-x86_64
Xcode: 4.6.2
CLT: 4.6.0.0.1.1365549073
GCC-4.2: build 5666
LLVM-GCC: build 2336
Clang: 4.2 build 425
X11: 2.7.4 => /opt/X11
System Ruby: 1.8.7-358
Perl: /usr/bin/perl
Python: /usr/local/bin/python => /usr/local/Cellar/python/2.7.4/Frameworks/Python.framework/Versions/2.7/bin/python2.7
Ruby: /usr/bin/ruby => /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby

Alguma ideia?