Multiprocessing code to calculate pi never finishes

Question

I want to calculate pi. The procedure is simple:

1. Make a 1x1 square and draw a circle in the square. Then divide by 4.
2. Take two random values (x, y).
3. If x² + y² ≤ 1 than the point is in the circle.
4. Repeat the above N times.
5. Count the inner points (I'll call it K) and divide by all number of executions and multiply by four. (4 * K / N == Pi)

The more iterations, the more accurate the calculation.

For doing fast, I use multiprocessing library. But the multiprocessing code never finishes. What's the problem?

import timeit
start = timeit.default_timer()

import random
from multiprocessing import Pool

N = 1000000
process_num = 4

def make_pi(end):
    count_inbound = 0
    for x in range(end):
        the_x = random.random()
        the_y = random.random()
        if((the_x**2 + the_y**2) <= 1):
            count_inbound += 1
    return count_inbound

# Multiprocessing.
p = Pool(processes = process_num)
count_in = p.map(make_pi, [N/process_num for x in range(process_num)])
print(4*sum(count_in)/N)

# Normal.
##print(4*make_pi(N)/N)

stop = timeit.default_timer()
print(stop - start)

Answer 1

Self answer.

the problem is process need to be closed.

so i add just one line.

if __name__ == "__main__":

than my code do work!

import timeit
start = timeit.default_timer()

import random
from multiprocessing import Pool

N = 1000000
process_num = 4

def make_pi(end):
    count_inbound = 0
    for x in range(end):
        the_x = random.random()
        the_y = random.random()
        if((the_x**2 + the_y**2) <= 1):
            count_inbound += 1
    return count_inbound

if __name__ == "__main__":
    #multiprocessing code
    p = Pool(processes = process_num)
    count_in = p.map(make_pi, [int(N/process_num) for x in range(process_num)])
    print(4*sum(count_in)/N)

    #normal code
    #print(4*make_pi(N)/N)

    stop = timeit.default_timer()
    print(stop - start)