Quick test of how multithreaded lua works

main.lua

for i = 1, 20 do
	print("Hello main thread world! " .. counter)
	counter = counter + 1;
end

multithreadLua.cpp

#include <lua.hpp>
#include <SFML/System.hpp>
#include <iostream>

#include <cstdlib> // system
#include <utility> // pair

// Execute a file. Print errors.
void dofile( std::pair<lua_State*, const char*> arguments )
{
    lua_State* const L = arguments.first;
    const char* const filename = arguments.second;
    if( luaL_dofile( L, filename ) ) // returns 0 on success
    {
        // If there was an error, it'll be on top of the stack.
        // Display and remove it.
        std::cout << lua_tostring( L, -1 ) << std::endl;
        lua_pop( L, 1 );
    }
}

int main(int argc, char** argv)
{
    // create two lua threads/states
    lua_State* mainState = lua_open();
    lua_State* sideState = lua_newthread( mainState ); // is now also on top of the main thread stack. shares globals.
    
    // open base libraries (e.g. print())
    luaL_openlibs( mainState );

    // initialize global counter
    lua_pushnumber( mainState, 0 );
    lua_setglobal( mainState, "counter" );

    // create two threads
    sf::Thread mainThread( dofile, std::make_pair( mainState, "../main.lua" ) );
    sf::Thread sideThread( dofile, std::make_pair( sideState, "../side.lua" ) );

    // launch them
    std::cout << "Launch!" << std::endl;
    mainThread.launch();
    sideThread.launch();

    // wait for them to finish
    mainThread.wait();
    sideThread.wait();

    // cleanup
    lua_close( mainState );

    // quick'n'dirty "press any key"
    system("pause");
    return 0;
}

side.lua

for i = 1, 20 do
	print("Hello side thread world! " .. counter)
	counter = counter + 1;
end