gen_fsm initial state, sending event to it on spawning

Question

If I want to always send an event to the initial state of a gen_fsm when I have spawned it, where should I put that function call? Right after start_link or from the process that invoked start_link in the first place. Are there any best practices here?

Answer 1

If you just want to alter the state of the FSM after you start it, you might simply implement the init function for your state machine:

Reading from: http://www.erlang.org/doc/man/gen_fsm.html#Module:init-1

Whenever a gen_fsm is started using gen_fsm:start/3,4 or gen_fsm:start_link/3,4, this function is called by the new process to initialize.

Args is the Args argument provided to the start function.

If initialization is successful, the function should return {ok,StateName,StateData}, {ok,StateName,StateData,Timeout} or {ok,StateName,StateData,hibernate}, where StateName is the initial state name and StateData the initial state data of the gen_fsm.

Also, using the init function, you're sure about the atomicity of the two functions (start_link and init). They will both succeed or fail.

Answer 2

I thik it is right to send first event from the process invoking FSM start function. Or return timeout = 0 from init/1 and handle 'timeout' event in the initial state.

On the other hand, it makes races possible if your gen_fsm is a rgistered process. If that is the case I would send message to the gen_fsm process PID from init/1 befor registering.