python - How do I make processes able to write in an array of the main program?

Question

I am making a process pool and each of them need to write in different parts of a matrix that exists in the main program. There exists no fear of overwriting information as each process will work with different rows of the matrix. How can i make the matrix writable from within the processes??

The program is a matrix multiplier a professor assigned me and has to be multiprocessed. It will create a process for every core the computer has. The main program will send different parts of the matrix to the processes and they will compute them, then they will return them in a way i can identify which response corresponds to which row it was based on.

Answer 1

Have you tried using multiprocessing.Array class to establish some shared memory?

See also the example from the docs:

from multiprocessing import Process, Value, Array

def f(n, a):
    n.value = 3.1415927
    for i in range(len(a)):
        a[i] = -a[i]

if __name__ == '__main__':
    num = Value('d', 0.0)
    arr = Array('i', range(10))

    p = Process(target=f, args=(num, arr))
    p.start()
    p.join()

    print num.value
    print arr[:]

Just extend this to a matrix of size h*w with i*w+j-style indexing. Then, add multiple processes using a Process Pool.