executor_test_1.py

"""
This one "Doesn't" work. Seems like `map` doesn't play well with
`as_completed`.
"""
import time
import random
from concurrent.futures import ThreadPoolExecutor, as_completed


def my_sleep(n=1000):
    ident = random.randint(0, 1000)
    print("Starting %s" % ident)
    time.sleep(n)
    print("Finished: %s" % ident)
    return ident


ex = ThreadPoolExecutor(max_workers=4)
res = ex.map(my_sleep, [1000, 3, 2, 1000])

for t in as_completed(res):
    print('##### Done: %s' % t)

executor_test_2.py

"""
This one works fine. `ex.submit` and `as_completed` play nicely together
"""
import time
import random
from concurrent.futures import ThreadPoolExecutor, as_completed


def my_sleep(n=1000):
    ident = random.randint(0, 1000)
    print("Starting %s" % ident)
    time.sleep(n)
    print("Finished: %s" % ident)
    return ident


ex = ThreadPoolExecutor(max_workers=4)

res = [
    ex.submit(my_sleep, n) for n in [100, 3, 2, 100]
]

for t in as_completed(res):
    print('##### Done: %s' % t)

output_1.txt

❯ python executor_test.py
Starting 633
Starting 340
Starting 194
Starting 307
Finished: 340  # Already Finished. Wasn't reported in line 22.
Finished: 194  # Already Finished. Wasn't reported in line 22.