Example of running blocking code in asyncio using default executor. There are four tasks each of them sleep from 1 to 4 seconds corresponding. If it were concurrent call then they would run for 1 + 2+ 3 + 4 = 10 seconds. However, running them in executor executes each task on separate thread and the total time to execute all of them took 4 secon…

asynio_blocking_code_default_executor.py

import asyncio
from time import sleep
import logging

logging.basicConfig(
    level=logging.DEBUG, format="%(asctime)s %(thread)s %(funcName)s %(message)s"
)


def long_task(t):
    """Simulate long IO bound task."""
    logging.info("2. t: %s", t)
    sleep(t)
    logging.info("4. t: %s", t)
    return t ** 2


async def main():
    loop = asyncio.get_running_loop()
    inputs = range(1, 5)
    logging.info("1.")
    futures = [loop.run_in_executor(None, long_task, i) for i in inputs]
    logging.info("3.")
    results = await asyncio.gather(*futures)
    logging.info("5.")
    for (i, result) in zip(inputs, results):
        logging.info("6. Result: %s, %s", i, result)


if __name__ == "__main__":
    asyncio.run(main())
    
# Output
# 2020-03-18 17:13:07,523 23964 main 1.
# 2020-03-18 17:13:07,524 5008 long_task 2. t: 1
# 2020-03-18 17:13:07,525 21232 long_task 2. t: 2
# 2020-03-18 17:13:07,525 22048 long_task 2. t: 3
# 2020-03-18 17:13:07,526 25588 long_task 2. t: 4
# 2020-03-18 17:13:07,526 23964 main 3.
# 2020-03-18 17:13:08,526 5008 long_task 4. t: 1
# 2020-03-18 17:13:09,526 21232 long_task 4. t: 2
# 2020-03-18 17:13:10,527 22048 long_task 4. t: 3
# 2020-03-18 17:13:11,527 25588 long_task 4. t: 4
# 2020-03-18 17:13:11,527 23964 main 5.
# 2020-03-18 17:13:11,528 23964 main 6. Result: 1, 1
# 2020-03-18 17:13:11,528 23964 main 6. Result: 2, 4
# 2020-03-18 17:13:11,529 23964 main 6. Result: 3, 9
# 2020-03-18 17:13:11,529 23964 main 6. Result: 4, 16