if nil == time_global then
  time_global = function () return device():time_global() end
end

function wait_game(time_to_wait)
     verify_if_thread_is_running()
     if (time_to_wait == nil) then
         coroutine.yield()
     else
         local time_to_stop = game.time() + time_to_wait
         while game.time() <= time_to_stop do
             coroutine.yield()
         end
     end
end