Pickle limitations for class based decorators.

failure.py

from concurrent.futures import ProcessPoolExecutor


class CheckOnlyIntegers:
    def __init__(self, fn):
        self.fn = fn

    def __call__(self, *args):
        if not all([type(arg) == int for arg in args]):
            raise ValueError("Invalid param is not an integer")
        return self.fn(*args)


@CheckOnlyIntegers  # this will change in the fixed version
def add(x, y):
    return x + y


with ProcessPoolExecutor(max_workers=3) as ex:
    futures = [
        ex.submit(add, *(2, 3)),
        ex.submit(add, *(9, 8)),
    ]
    for future in futures:
        print(future.result(timeout=3))

fixed.py

from concurrent.futures import ProcessPoolExecutor


class CheckOnlyIntegers:
    def __init__(self, fn):
        self.fn = fn

    def __call__(self, *args):
        if not all([type(arg) == int for arg in args]):
            raise ValueError("Invalid param is not an integer")
        return self.fn(*args)


def add(x, y):
    return x + y

alternate_add = CheckOnlyIntegers(add)  # Used instead of decorator

with ProcessPoolExecutor(max_workers=3) as ex:
    futures = [
        ex.submit(alternate_add, *(2, 3)),
        ex.submit(alternate_add, *(9, 8)),
    ]
    for future in futures:
        print(future.result(timeout=3))