concurrent-future-callback.py

from concurrent.futures import ThreadPoolExecutor
import time

def wait_function(x, y):
    print('Task(', x,'multiply', y, ') started')
    time.sleep(2)
    print('Task(', x,'multiply', y, ') completed')
    return x * y

def callback_function(future):
    print('Callback with the following result', future.result())

with ThreadPoolExecutor(max_workers=1) as executor: #change max_workers to 2 and see the results
    future = executor.submit(wait_function, 3, 4)
    future.add_done_callback(callback_function)
    future2 = executor.submit(wait_function, 8, 8)
    while True:
        if(future.running()):
            print("Task 1 running")
        if(future2.running()):
            print("Task 2 running")

        if(future.done() and future2.done()):
            print(future.result(), future2.result())
            break