'function i register
Public Function Print(ByVal lua_state As IntPtr) As Integer
    Console.WriteLine(clua.GetString(-1))
End Function

'how i register a function
clua.RegisterCfunction("print", AddressOf Print)

Public Sub RegisterCfunction(ByVal refname As String, ByVal func As LuaCFunction)
    register(cLuaState, refname, func)
End Sub

Friend Sub register(ByVal lua_state As IntPtr, ByVal name As String, ByVal func As LuaCFunction)
    Dim top As Integer = lua_gettop(lua_state) 'upvalues
    lua_pushcclosure(lua_state, func, top)
    lua_setfield(lua_state, LUA_GLOBALSINDEX, name)
End Sub

'lua code
function test(duration)
    print('timer started: '..duration..' seconds')
    local inittime = os.time()
    local curtime = os.time()
    while curtime - inittime < duration do
        curtime = os.time()
        coroutine.yield()
    end
    print('timer exited')
end

co = coroutine.create(test)
coroutine.resume(co,5)
while coroutine.status(co) == 'suspended' do
coroutine.resume(co)
end