with ProcessPoolExecutor() as executor:
    future1 = executor.submit(function1, arg1, arg2)
    future2 = executor.submit(function2, arg1)
    future3 = executor.submit(function3, arg1)

    for future in as_completed([future1, future2, future3]):
        if future == future1:
            res1 = future.result()
        elif future == future2:
            res2 = future.result()
        elif future == future3:
            res3 = future.result()