Python multiprocessing with function of functions

I want to use multiprocessing python module to parallelize a customized function, which itself contains other customized functions (see the code below). Let's supose I have 100 elements and I want to compute 10 each batch, then I will use 10 processes. However I notice that the multiprocessing first calculate my_subfunction1 for the 100 elements before passing to my_subfunction2, and subsequently.

Why is this happening and is there any way to prevent this behaviour? I would like to calculate my_subfunction1, 2, and 3 for 10 elements each batch.

Thanks so much in advance for the help.

import multiprocessing as mp

with mp.get_context('spawn').Pool(processes = 10) as pool:
    try:
        res = pool.starmap(my_main_function, args)
    except Exception as e:
        pool.terminate()
        raise e 

def my_main_function(my_args):
    res1 = my_subfunction1(arg1)
    res2 = my_subfunction2(res1)
    res3 = my_subfunction3(res2)
    
    return res3

You need Python's Pool object from the multiprocessing library. The Pool object:

> offers a convenient means of parallelizing the execution of a function
> across multiple input values, distributing the input data across
> processes (data parallelism).

import multiprocessing as mp

def my_main_function(arg):
    res1 = (lambda x: x + 1)(arg)
    res2 = (lambda x: x * 2)(res1)
    res3 = (lambda x: x ** 2)(res2)
    return res3

if __name__ == '__main__':
    args = range(100)
    
    with mp.Pool(processes=10) as pool:
        res = pool.map(my_main_function, args)
        print(res)

Result:

[4, 16, 36, 64, 100, 144, 196, 256, 324, 400, 484, 576, 676, 784, 900, 1024, 1156, 1296, 1444, 1600, 1764, 1936, 2116, 2304, 2500, 2704, 2916, 3136, 3364, 3600, 3844, 4096, 4356, 4624, 4900, 5184, 5476, 5776, 6084, 6400, 6724, 7056, 7396, 7744, 8100, 8464, 8836, 9216, 9604, 10000, 10404, 10816, 11236, 11664, 12100, 12544, 12996, 13456, 13924, 14400, 14884, 15376, 15876, 16384, 16900, 17424, 17956, 18496, 19044, 19600, 20164, 20736, 21316, 21904, 22500, 23104, 23716, 24336, 24964, 25600, 26244, 26896, 27556, 28224, 28900, 29584, 30276, 30976, 31684, 32400, 33124, 33856, 34596, 35344, 36100, 36864, 37636, 38416, 39204, 40000]