Class variables and Multiprocessing(or concurrent.futures.ProcessPoolExecutor)

[Tomli]

Hello everyone!

The last code that I was working on was very taxing and slow, so I decided to optimize it by using multiprocessing. When I did this, I discovered that somehow class variables that have been changed in code before calling ProcessPoolExecutor aren't taken into account when instantiating the processes. As an example, I prepared the following code:

import concurrent.futures

class test():
    class_variable = None

    def test_method(self,iter):
        print(test.class_variable)
    
if __name__=='__main__':
    test.class_variable = 1
    inst = test()
    print(f"Class variable before pool: {test.class_variable=}")
    with concurrent.futures.ProcessPoolExecutor() as executor:
        executor.map(inst.test_method,[x for x in range(5)])

If you run this code, the results are:
Class variable before pool: test.class_variable=1
test.class_variable=None
test.class_variable=None
test.class_variable=None
test.class_variable=None
test.class_variable=None

As I said at the start, even if we change the class variable before using multiprocessing they will be ignored and the code will use the original value (None in this case).

I wanted to know if someone knows a way to make the processes take into account the change in class variables.