English is not my native language, but I try to post my problem for answer.
Recently, I found an interesting thing about "static variable". I have only one extension as room extension and the client (unity engine) would send "room creation request", in order to create the room for playing game. Originally, I think if I set a static variable such as "game time", this variable is shared in each room. But it's not truth, the static variable in each room is independent.
I try to google the reason, I supposed that server create a thread when creating a room. Is it right?