Show threadpool processes only max_workers tasks at the same time and behaves like a queue

threadpool_queue.py

# Show threadpool processes only max_workers tasks at the same time and behaves
# like a queue
import itertools
from concurrent import futures
from io import StringIO
from time import sleep


def print_sleep_print(p, out):
    print("(", file=out, end="")
    sleep(0.01)
    print(")", file=out, end="")


def run_in_threadpool(max_workers):
    out = StringIO()
    with futures.ThreadPoolExecutor(max_workers=max_workers) as pool:
        pool.map(print_sleep_print, range(20), itertools.repeat(out))

    out.seek(0)
    return out.read()

for i in range(2, 5):
    print(i, run_in_threadpool(i))

# prints:
# 2 (()()()()()()()()()()()()()()()()()()())
# 3 ((()()()()()()()()()()()()()()()()()()))
# 4 (((()()()()()()()()()()()()()()()()())))