A proof of concept: atomics over shared memory

_testatomic.pyx

#!/usr/bin/env cython

# SPDX-FileCopyrightText: 2026 Ilya Egorov <0x42005e1f@gmail.com>
# SPDX-License-Identifier: 0BSD

# cython: freethreading_compatible = True
# cython: subinterpreters_compatible = own_gil
# distutils: extra_compile_args = -DCYTHON_USE_MODULE_STATE=1


cdef extern from "stdatomic.h" nogil:
    cdef enum memory_order:
        memory_order_relaxed

    char atomic_fetch_add_explicit(char *obj, char arg, memory_order order)


cpdef char fetch_inc(char[:] mem) nogil:
    return atomic_fetch_add_explicit(&mem[0], 1, memory_order_relaxed)

testatomic.py

#!/usr/bin/env python3

# SPDX-FileCopyrightText: 2026 Ilya Egorov <0x42005e1f@gmail.com>
# SPDX-License-Identifier: 0BSD

import os
import time

from concurrent.futures import (
    InterpreterPoolExecutor,
    ProcessPoolExecutor,
    ThreadPoolExecutor,
)
from multiprocessing import RawArray, set_start_method

from _testatomic import fetch_inc

arr = RawArray("B", [0])
mem = memoryview(arr).cast("B")


def work(mem=None):
    if mem is None:  # thread | process (fork)
        fetch_inc(arr)
    else:  # subinterpreter
        fetch_inc(mem)


def main():
    expected = 0

    for cls in [
        ThreadPoolExecutor,
        InterpreterPoolExecutor,
        ProcessPoolExecutor,
    ]:
        start = time.perf_counter()

        with cls(n := min(max(4, os.process_cpu_count()), 256)) as executor:
            while time.perf_counter() - start < 1:  # one second
                expected += n
                expected %= 256

                if cls is InterpreterPoolExecutor:
                    futures = [executor.submit(work, mem) for _ in range(n)]
                else:
                    futures = [executor.submit(work) for _ in range(n)]

                exceptions = []

                for future in futures:
                    if future.exception() is not None:
                        exceptions.append(future.exception())

                if exceptions:
                    msg = "unhandled errors from workers"
                    raise BaseExceptionGroup(msg, exceptions)

                assert expected == mem[0], f"{expected} != {mem[0]}"

            print(f"{cls.__name__}: passed")


if __name__ == "__main__":
    set_start_method("fork")
    main()

Interesting, thanks. Perhaps it would be worth including a copyright notice and some information about the changes required by PSF-2.0 for the borrowed files. But overall, I understand the idea.

Interesting, thanks. Perhaps it would be worth including a copyright notice and some information about the changes required by PSF-2.0 for the borrowed files. But overall, I understand the idea.

I'll be sure to update the license a little later.

After seeing my old attempts of trying to bridge atomics to cython I think I'm going to make it so that there is a better unified system for atomics vs the one python provides for 3.13+. One of the things that I do not like about python's version is that the code doesn't feel completely natural at all and the functions have some pretty unusual names given. I did have the idea however of making my own version as a C Library that could be a header only that I would call "uatomics.h" meaning unified atomics that could contain proper msvc, gcc & std support. This way the process of binding everything to cython can be a bit easier with the benefit of binding it to other languages for users who end up needing it, an example would be NodeJS.