atomic_py.c

#include <pthread.h>
#include <stdio.h>

#include "Python.h"

#define atomic_int_add(ptr, val) __sync_add_and_fetch(&ptr, val)

static PyObject*
int_add(PyObject *self, PyObject *args)
{
    int avalue, bvalue;
    if (!PyArg_ParseTuple(args, "ii", &avalue, &bvalue)) 
	return NULL;
    return Py_BuildValue("i", atomic_int_add(avalue, bvalue));
}

static PyMethodDef AtomicMethods[] = {
    {"int_add", int_add, METH_VARARGS, "Atomically increment an integer"},
    {NULL, NULL, 0, NULL}
};

PyMODINIT_FUNC
initatomic(void)
{
    Py_InitModule("atomic", AtomicMethods);
}

setup.py

from setuptools import setup, Extension

atomic = Extension('atomic',
                   sources=['atomic_py.c'])

setup(name='AtomicPy',
      version='dev',
      ext_modules=[atomic]
      )

test.py

"""
Run test.py with 1 for atomic, 0 for non-AtomicWorker
"""
import sys
import threading

import atomic

foo = 0


class Worker(threading.Thread):
    def run(self):
        global foo
        while foo < 100:
            foo += 1
            print foo


class AtomicWorker(threading.Thread):
    def run(self):
        global foo
        while foo < 100:
            foo = atomic.int_add(foo, 1)
            print foo


def main(atomic):
    workers = {}
    for _ in range(2):
        if atomic:
            thread = AtomicWorker()
        else:
            thread = Worker()
        thread.start()
        workers[thread.name] = thread
    for _, worker in workers.items():
        worker.join()

if __name__ == '__main__':
    sys.setcheckinterval(0)
    main(atomic=eval(sys.argv[1]))