Demonstrates the use of futures in python 3

futures.py

from concurrent.futures import ThreadPoolExecutor
from time import sleep

executor = ThreadPoolExecutor(max_workers=10)
MAX_RUN_TIME = 4.5
SLEEP_BETWEEN_WAITS = 0.1


def return_slept(sleep_time):
    sleep(sleep_time)
    return sleep_time


def main():
    futures = [executor.submit(return_slept, 1.3), executor.submit(return_slept, 2.1)]

    results = []
    futures_running = []
    time_slept = 0.0
    while time_slept < MAX_RUN_TIME:
        futures_running.clear()
        for future in futures:
            if future.done():
                # Future is done, append the result.
                results.append(future.result())
            else:
                # The future is still running, so wait in the next loop
                futures_running.append(future)

        # If there are no more futures, stop the loop.
        if len(futures_running) == 0:
            break
        # Otherwise, overwrite the futures list with the list of running futures
        futures = futures_running.copy()
        # And sleep for the maximum amount of time.
        sleep(SLEEP_BETWEEN_WAITS)
        time_slept += SLEEP_BETWEEN_WAITS

    print("Completed after <= {0} seconds".format(time_slept))

    # Cancel the remaining futures.
    for future in futures_running:
        print("Cancelling future " + str(future))
        future.cancel()

    print(str(results))

if __name__ == '__main__':
    main()