Transition with the same event in multiple regions

[Balint-Ivanics-KUKA]

Hi,

Multiple regions of the same state machine using the same event for transition don't react as I would expect based on the docs.
"Whether you send one event or multiple events, result is always a sequence of results. This is so because in a presence multiple reqions, results will come back from multiple machines in those regions. This is shown with method sendEventCollect which gives a list of results." To me this suggested that multiple regions can accept the event but it looks like that is not the case.

If I have the following state machine:

    public void configure(StateMachineStateConfigurer<MyStateMachineState, MyStateMachineEvent> states)
            throws Exception
    {
        states
                .withStates()
                .initial(BasicState.ROOT)
                .and()
                .withStates()
                .parent(BasicState.ROOT)
                .region("region1")
                .initial(BasicState.CHILD11)
                .state(BasicState.CHILD12)
                .and()
                .withStates()
                .parent(BasicState.ROOT)
                .region("region2")
                .initial(BasicState.CHILD21)
                .state(BasicState.CHILD22);
    }

    public void configure(StateMachineTransitionConfigurer<MyStateMachineState, MyStateMachineEvent> transitions)
            throws Exception
    {
        transitions
                .withExternal().source(BasicState.CHILD11).target(BasicState.CHILD12).event(BasicEvent.EVENT)
                .and()
                .withExternal().source(BasicState.CHILD21).target(BasicState.CHILD22).event(BasicEvent.EVENT);
    }

then if I send a BasicEvent.EVENT only one of the regions will transition. I would have expected both to transition.

Is this the intended behavior?

Thanks

[manhnt217]

I'm new to Spring state machine. I'm experiencing the same behaviour.

[wlfbck]

I'm seeing something similar here. I can actually reliably trigger either both regions transitioning or only one by adding/removing an action to that transition.
The code is nothing special, simply a state machine with two regions (order and ncprogram) which listen to the same event (also named order). Ignore the second event named ncprogram, it is not relevant to the problem. I'm adding an actionFunction() to the order transition to get the second log.

Log without action (this is the expected output):

10:38:15,694 INFO  ContextGenerator            [] - Receiving event order
10:38:15,713 INFO  StateMachineLogger          [] - transition 'order-canExist to order-exists' triggered by event 'order'
10:38:15,715 INFO  StateMachineLogger          [] - stateChanged from 'order-canExist' to 'order-exists'
10:38:15,717 INFO  StateMachineLogger          [] - transition 'ncprogram-cannotExist to ncprogram-canExist' triggered by event 'order'
10:38:15,717 INFO  StateMachineLogger          [] - stateChanged from 'ncprogram-cannotExist' to 'ncprogram-canExist'
10:38:15,717 INFO  ContextGenerator            [] - Receiving event ncprogram
10:38:15,718 INFO  StateMachineLogger          [] - eventNotAccepted: ncprogram
10:38:15,719 INFO  StateMachineLogger          [] - transition 'ncprogram-canExist to ncprogram-exists' triggered by event 'ncprogram'
10:38:15,719 INFO  StateMachineLogger          [] - stateChanged from 'ncprogram-canExist' to 'ncprogram-exists'
10:38:15,720 INFO  StateMachineLogger          [] - eventNotAccepted: ncprogram

Log with action attached to transition (ncprogram region is not transitioning at all):

10:38:35,423 INFO  ContextGenerator            [] - Receiving event order
10:38:35,446 INFO  StateMachineLogger          [] - transition 'order-canExist to order-exists' triggered by event 'order'
10:38:35,448 INFO  StateMachineLogger          [] - stateChanged from 'order-canExist' to 'order-exists'
10:38:35,456 INFO  StateMachineLogger          [] - eventNotAccepted: order
10:38:35,457 INFO  StateMachineLogger          [] - eventNotAccepted: order
10:38:35,457 INFO  ContextGenerator            [] - Receiving event ncprogram
10:38:35,457 INFO  StateMachineLogger          [] - eventNotAccepted: ncprogram
10:38:35,457 INFO  StateMachineLogger          [] - eventNotAccepted: ncprogram
10:38:35,457 INFO  StateMachineLogger          [] - eventNotAccepted: ncprogram
10:38:35,458 INFO  StateMachineLogger          [] - eventNotAccepted: ncprogram
10:38:35,458 INFO  StateMachineLogger          [] - eventNotAccepted: ncprogram

edit:
@jvalkeal I found the issue, and imho is something that needs changing. When exception occurs during the action, it is completely invisible to the user (even when having a StateMachineListener which prints everything) that this happens. Sure, it might be somewhere inside the Flux stuff, but the whole documentation always does sendEvent(..).subscribe() which means you never actually get to see/use StateMachineEventResult.
So another sendEvent message would be nice, which does the subscribe() for you and returns List<StateMachineEventResult<..>> . A shorthand for stateMachine.sendEvent(Mono.just(message)).collectList().block(); if you will. Also the documentation might need updating in that regard, as someone who has never used Flux before this was pretty intransparent.