Python Multiprocessing or Thread

Question

My code

import time
from multiprocessing.pool import ThreadPool
from concurrent.futures import ThreadPoolExecutor
def print_function(tests):
    while True:
        print tests
        time.sleep(2)


executor = ThreadPoolExecutor(max_workers=2)

for i in range(5):
    a = executor.submit(print_function(i))

output 0 0 0 0 0 0 0 0...

but I want out 012345, 012345, 012345...

How can I do this ?

Answer 1

In the line

a = executor.submit(print_function(i))
                    ^^^^^^^^^^^^^^^^^

you are calling the function already. Since it has a while True, it will never finish and thus submit() will never be reached.

The solution is to pass the function as a reference and the argument separately:

a = executor.submit(print_function, i)

However, notice that you will not get the output you like (012345), since a) the range will stop at 4 and b) you kick off only 2 workers and c) the operating system will choose which process to run, so that will be seemingly random (more like 310254).