Re: Why use send_after to send a message is reverse？
Isn't it obvious? Appending head is O(1) operation, removing head is also O(1) operation. Since there is not any guarantee in which order messages should be returned, it is the obvious simplest solution. Your testing code is very uncommon in a real application. There are usually two different processes which schedule messages and the effect is unnoticeable because their ordering is not defined.