Use numpy array in shared memory for multiprocessing

Question

I would like to use a numpy array in shared memory for use with the multiprocessing module. The difficulty is using it like a numpy array, and not just as a ctypes array.

Answer 1

You can use the sharedmem module: https://bitbucket.org/cleemesser/numpy-sharedmem

Here's your original code then, this time using shared memory that behaves like a NumPy array (note the additional last statement calling a NumPy sum() function):

from multiprocessing import Process
import sharedmem
import scipy

def f(a):
    a[0] = -a[0]

if __name__ == '__main__':
    # Create the array
    N = int(10)
    unshared_arr = scipy.rand(N)
    arr = sharedmem.empty(N)
    arr[:] = unshared_arr.copy()
    print "Originally, the first two elements of arr = %s"%(arr[:2])

    # Create, start, and finish the child process
    p = Process(target=f, args=(arr,))
    p.start()
    p.join()

    # Print out the changed values
    print "Now, the first two elements of arr = %s"%arr[:2]

    # Perform some NumPy operation
    print arr.sum()