example.py

import threading
from ctypes import cdll
lib = cdll.LoadLibrary('./liblib.so')


class Foo(object):
    def __init__(self):
        self.obj = lib.Foo_new()

    def bar(self):
        lib.Foo_bar(self.obj)


def run():
    f = Foo()
    f.bar()


threading.Thread(target=run).start()
threading.Thread(target=run).start()
threading.Thread(target=run).start()
p = threading.Thread(target=run)
p.start()
p.join()

lib.cpp

// g++ -c -fPIC lib.cpp -o lib.o
// g++ -shared -Wl,-soname,liblib.so -o liblib.so  lib.o


#include <iostream>

class Foo{
    public:
        void bar(){
            std::cout << "Start" << std::endl;
            for(int i=0;i<100000000;i++) {
            	for(int j=0;j<100000000;j++) {}
            }
            std::cout << "End" << std::endl;
        }
};

extern "C" {
    Foo* Foo_new(){ return new Foo(); }
    void Foo_bar(Foo* foo){ foo->bar(); }
}