How to execute function parallel : Python

Question

I am trying to execute below code in parallel using multiprocessing but I am not getting proper output.

Iteration with 1 and iteration with 5 should happen in parallel

from multiprocessing import Pool
def func1(x):
    i = x
    while i < 10:
        print(str(i)+" fun1")
        i +=1

if __name__ == '__main__':
    pool = Pool(processes=1) 
    pool.map(func1, [1,5])

Result I got: happening more iterations

1 fun1 2 fun1 3 fun1 4 fun1 5 fun1 6 fun1 7 fun1 8 fun1 9 fun1 5 fun1 6 fun1 7 fun1 8 fun1 9 fun1

Expected output: both iterations should happen in parallel

1 fun1 5 fun1 2 fun1 6 fun1 3 fun1 7 fun1 4 fun1 8 fun1 5 fun1 9 fun1 6 fun1 7 fun1 8 fun1 9 fun1

i updated the question please have a look

LUZO
– LUZO

2018-12-15 16:31:42 +00:00
Commented Dec 15, 2018 at 16:31 — LUZO
– LUZO, Commented Dec 15, 2018 at 16:31

xer-t · Accepted Answer · 2018-12-15 17:08:20Z

1

I can't reproduce your result with your code. I'm getting the expected behavior (note the call of 'func1' before the 'if' statement):

1 fun1 2 fun1 3 fun1 4 fun1 5 fun1 6 fun1 7 fun1 8 fun1 9 fun1 1 fun1 2 fun1 3 fun1 4 fun1 5 fun1 6 fun1 7 fun1 8 fun1 9 fun1 5 fun1 6 fun1 7 fun1 8 fun1 9 fun1

For some reason, you're calling func1(1) three times.

In any case, you start 1 process only, so the execution will be serial. You need more than one process to get parallel execution.

answered Dec 15, 2018 at 17:08

xer-t

613 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

LUZO Over a year ago

i have updated the code can you please have a look...i used 2 process but still same result

xer-t Over a year ago

are you expecting an alternate printing? If so, it is very unlikely if you do not force the processes to wait the others.

acesaran · Accepted Answer · 2018-12-15 16:00:24Z

1

What you are expecting is not happening due to the Global Interpreter Lock. Give it a look: https://wiki.python.org/moin/GlobalInterpreterLock

answered Dec 15, 2018 at 16:00

acesaran

113 bronze badges

1 Comment

Yann Vernier Over a year ago

multiprocessing works around that by using multiple processes, each of which has its own lock. I'd say the processes=1 is what restricts this code, as well as the simple fact the job is so short one may finish before the other is told what to do. Thirdly, the job isn't productive; map would normally collect the return values.

Collectives™ on Stack Overflow

How to execute function parallel : Python

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related