how to handle termination of gen_fsm

Question

I have a MAIN process that spawn an implementation of a gen_fsm behavior, but this MAIN process is not an implementation of supervisor behavior, its just another module. Let say the implementation of gen_fsm is called GAME_ROOM. My case is like this:

1. When ever there are 3 peoples ready, the MAIN process will spawn a new GAME_ROOM.
2. I use gen_fsm:start_link function to initiate a new GAME_ROOM, so if the GAME_ROOM exit by error, my MAIN process could spawn a new one, to replace the downed process.
3. I managed to make my MAIN process detect the EXIT event of all downed GAME_ROOM

The problem is: I need to restore all downed GAME_ROOM states at the new one. My question is: How can I use gen_fsm's terminate function to pass the latest states of the gen_fsm to my MAIN process, so when I respawn a new GAME_ROOM, I can pass that states?

Answer 1

One simple way would be for GAME_ROOM terminate/3 to send a message with the necessary state information to MAIN. For this to work the GAME_ROOM must know the pid of MAIN (easy) and you have to be certain that terminate/3 is really called.

Answer 2

Read about process_flag ({trap_exit, true}) and handle info 'EXIT'.

Answer 3

First of all, I would really suggest you to look at using supervisors in your implementation, to avoid re-inventing the wheel.

A possibility could be to create an ETS table in your MAIN, so you can store data from within your gen_fsms which can survive process crashes.

Answer 4

My belief is that if GAME_ROOM exits because of an error, there is nothing to save (how do you know your state is valid, otherwise you would trap the error inside GAME_ROOM).