Shared data between two pybind11 modules

bar.cpp

#include <pybind11/pybind11.h>

#include "SharedCounter.h"

PYBIND11_MODULE(bar, m) {
	m.def("inc", []() { return SharedCounter::getInstance().inc(); });
}

build.sh

g++ -shared SharedCounter.cpp -o libSharedCounter.so
g++ -O3 -Wall -shared -std=c++11 -fPIC -I. -I`python3-config --includes` foo.cpp -L. -lSharedCounter -o foo`python3-config --extension-suffix`
g++ -O3 -Wall -shared -std=c++11 -fPIC -I. -I`python3-config --includes` bar.cpp -L. -lSharedCounter -o bar`python3-config --extension-suffix`

LD_LIBRARY_PATH=`pwd` python3

CMakeLists.txt

cmake_minimum_required(VERSION 3.8)
project(example)

add_subdirectory(pybind11)

add_library(shared_counter SharedCounter.cpp)
target_compile_features(shared_counter PUBLIC cxx_std_11)

pybind11_add_module(foo foo.cpp)
target_link_libraries(foo PRIVATE shared_counter)

pybind11_add_module(bar bar.cpp)
target_link_libraries(bar PRIVATE shared_counter)

foo.cpp

#include <pybind11/pybind11.h>

#include "SharedCounter.h"

PYBIND11_MODULE(foo, m) {
	m.def("inc", []() { return SharedCounter::getInstance().inc(); });
}

output.txt

gives me
 [/c/Users/sam/Dropbox/pybind_example][sam]  $ cat test.py
import foo
import bar

print(foo.inc())
print(bar.inc())
print(foo.inc())
print(bar.inc())

[/c/Users/sam/Dropbox/pybind_example][sam]  $ python.exe test.py
0
0
1
1

SharedCounter.cpp

#include "SharedCounter.h"

SharedCounter &SharedCounter::getInstance() {
	static SharedCounter instance;
	return instance;
}

SharedCounter.h

class SharedCounter {
public:
	static SharedCounter &getInstance();

	int inc() { return m_counter++; }

private:
	SharedCounter() = default;

	int m_counter;
};