Problem with multiple scripts and Lua Threads

Question

When I have two scripts with the same function names and arguments run in different threads with SUPPOSEDLY different environments, the second thread ends up overwriting the definitions of the first and the first thread's state gets garbage collected!

// My thread instancing function
lua_State* LuaInstance::RunInstance(const std::string& fileName)
{
  lua_State* L = lua_newthread(m_state); 

  // Give new thread it's own global table
  lua_newtable(L);
  lua_newtable(L);
  lua_pushliteral(L, "__index");
  lua_pushvalue(L, LUA_GLOBALSINDEX);  // Original globals
  lua_settable(L, -3);
  lua_setmetatable(L, -2);
  lua_replace(L, LUA_GLOBALSINDEX);    // Replace LB's globals

  // Run script off new thread
  luaL_dofile(L, fileName.c_str());

  return L;
}

I'm basically trying to get it so that I can call multiple scripts like this (For a game engine):

-- Script 1
function Init(self)
  -- Do some stuff
end


-- Script 2
function Init(self)
  -- Do some other stuff
end

Answer 1

As it says in the manual, a the state created by new thread shares global state with other threads. If you want per-thread storage you'll have to create a special key to use in the registry.

From the manual (emphasis mine):

lua_State *lua_newthread (lua_State *L);

Creates a new thread, pushes it on the stack, and returns a pointer to a lua_State that represents this new thread. The new state returned by this function shares with the original state all global objects (such as tables), but has an independent execution stack. There is no explicit function to close or to destroy a thread. Threads are subject to garbage collection, like any Lua object.