Getting `BrokenProcessPool` error in a `concurrent.futures` example - python-3.x

Question

The example I am running is mentioned in this PyMOTW3 link. I am reproducing the code here:
from concurrent import futures
import os
def task(n):
return (n, os.getpid())
ex = futures.ProcessPoolExecutor(max_workers=2)
results = ex.map(task, range(5, 0, -1))
for n, pid in results:
print('ran task {} in process {}'.format(n, pid))
As per source, I am supposed to get following output:
ran task 5 in process 40854
ran task 4 in process 40854
ran task 3 in process 40854
ran task 2 in process 40854
ran task 1 in process 40854
Instead, I'm getting a long message with following concluding line -
concurrent.futures.process.BrokenProcessPool: A process in the process pool was terminated abruptly while the future was running or pending.
I am using Windows machine and running Python 9. All other examples are otherwise running fine. What is going wrong here?

Answer 1

I've finally been able to resolve the issue. The issue seems to be Windows specific. Following a related Stack Overflow post, I used if __name__=="__main__" idiom. The modified code is:
from concurrent import futures
import os
def task(n):
return (n, os.getpid())
def main():
ex = futures.ProcessPoolExecutor(max_workers=2)
results = ex.map(task, range(5, 0, -1))
for n, pid in results:
print('ran task {} in process {}'.format(n, pid))
if __name__ == '__main__':
main()
It worked, although I'm still not sure why this worked.