Hi Christophe I'm using boost trunk from yesterday And I have modified my example to use your suggestion : Row < SubRunning , event3 , none , Defer , none /* or guard */ > will do. Well, there is a small bug, but not where you expect it. It seems that the processing continues even though this transition defers the event. I just fixed this in the trunk (rev. 75641). Here is the execution output of the example attached : MS1 Entering State: Idle by: event1 MS1 Leaving State: Idle by: event1 MS1 Entering State: SubRunning by: event1 FwdGuard: returns:1, event: event2 Processing BaseEvent Instance(event2) Setting guard false FwdGuard: returns:0, event: event3 MS1 DEFERED: event3 FwdGuard: returns:0, event: event4 FwdGuard: returns:0, event: event3 MS1 DEFERED: event3 FwdGuard: returns:0, event: event5 MS1 Leaving State: SubRunning by: event5 MS1 Entering State: AfterSub by: event5 MS1 no_transition event (event3) It seems that the bug not fixed ... but this is my least worries ( partly my fault You have asked me to test it for you .... but I did not sorry about that). My bigger problem is the interpretation of no_transition you saying that it is an error situation... Well I have in my code a lot of situation when there are signals which are not interested to my state machine but they are dispatched to me anyhow our modules are used by different places for different purposes and there are signals which are useful in one case but not needed for my purpose I just simply ignore them these are ending up in no_transition so there I just write a log entry that signal is not handled so for me it is not an error at all it is the intended behavior. Now back to the My blocking problem ..... We use at the moment about 36 MSM state machines out of this 26 are performing specific well defined configuration task these 26 state-machine are nested to each in to each other to perform complicated behaviors sometimes there are nesting goes done to 5 level deep. We have, I call them main state machines which are connect these small task to each other to build complex behavior. We have more than 500 different row entries spitted in to these state machines. At the beginning we try to use MSM way of state machine nesting and soon we figured out that there is no compiler in the word which can compile/link this code. Than I have decided to make smaller compile unit and make each state machine as a separate compile unit and let communicate them over a simple interface. Yes this slows done the dispatching because we have to re-dispatch each event in run-time as many times as many nesting level we have. But this tread of is acceptable. And yes this way state machines are holding references to outer state machines if it is running as a nested state machine and states which are nested state machines are holding references to inner state machine instances. Every state machine uses the same interface to communicate and we hide the construction of the state machines with factories. So this way the outer does not exposed to the inner the inner does not exposed to the outer leads us to a compile-able code :). In case the state machine is in a stare where the sate is actually a holder of an inner state machine there is a Row with a baseEvent which this case re-dispatches the event to the inner one. Now if the inner one does not handles the event it shall send it back to the outer one. My assumption was that I can use the no_transition for this purpose but the implementation turns out different :(. For me name no_transition suggests that if no transition triggered. This function will be called and if the guard rejects the transition than this means to me that the transition is not triggered. Anyhow we could argue on it but in the end it does not help with my problem .... I would like to ask you to change the implementation .... if it is possible ..... :) I think my way would help in case of debugging because if the state machine does not triggered a transition at least the user has a chance to log it or do something with it .... I find it very annoying if an event is "eaten by a state machine without knowing what happened" If you disagree than please help me to find a way to get around of my problem .... I see 3 way out of it : 1. change the implementation of no_transition triggering. 2. provide a new function something like default_transition which is called if the transaction table( including rejected transitions by guards ) or states (deferral) are not handling the event. 3. A special row something like Row < AllState, AllEvent, None, MYDefaultTrans, None> eg give a last default trans option to the user to handle the event. Or if you have any better idea how to compile my code ?. Thanks for your help .... Cheers Richard On 23 November 2011 21:49, Christophe Henry <christophe.j.henry@googlemail.com> wrote:
Hi Richard,
the attached example I think shows 2 problems.
1st is that the deferral of event3 is not happening. 2nd is that the no_transition function is never called.
the output of the run is :
MS1 Entering State: Idle by: event1 MS1 Leaving State: Idle by: event1 MS1 Entering State: SubRunning by: event1 FwdGuard: returns:1, event: event2 Processing BaseEvent Instance(event2) Setting guard false FwdGuard: returns:0, event: event3 FwdGuard: returns:0, event: event4 FwdGuard: returns:0, event: event5 MS1 Leaving State: SubRunning by: event5 MS1 Entering State: AfterSub by: event5
I think it shall be :
MS1 Entering State: Idle by: event1 MS1 Leaving State: Idle by: event1 MS1 Entering State: SubRunning by: event1 FwdGuard: returns:1, event: event2 Processing BaseEvent Instance(event2) Setting guard false FwdGuard: returns:0, event: event3 FwdGuard: returns:0, event: event4 MS1 no_transition event (event4) MS1 Leaving State: SubRunning by: event5 MS1 Entering State: AfterSub by: event5 MS1 no_transition event (event3)
So in this example event3 and event4 are never triggered a transition ... the Row < SubRunning , baseEvent , none , ProcessBaseEvent , FwdGuard
was guarded by the FwdGuard for these events.
Is my expected behavior wrong ?
Well, hard to answer because the Standard does not discuss conflicts between a state declaration and a transition, so your guess is as good as mine ;-)
Let's say that this is the intended behavior. In the current implementation, the state declaration has the lowest priority. This means the transition table comes first, and if it handles the event, then processing stops here so your deferred declaration has no effect.
The answer to the question in your title is yes. If a guard rejects the event, the event is really handled (rejection is a perfectly acceptable event handling) so there is no call to no_transition, which is to be seen as a catch-all error handler in case you forget to handle an event. Seeing that the default version is an assert, imagine what you'd get at every guard rejection ;-)
If guard is executed but the transition actually is triggered because it is guarded out why this event treated as handled event ?.
Because a guard is not an error, a call to no_transition probably is. I think the best way to solve the conflict between state declaration and the transition table wanting to process is to state what you want in the transition table itself:
Row < SubRunning , event3 , none , Defer , none /* or guard */ >
will do.
Well, there is a small bug, but not where you expect it. It seems that the processing continues even though this transition defers the event. I just fixed this in the trunk (rev. 75641).
This 2 problems breaks my current nested state machine implementation because I'm using no_transition to forward the event to the outer state machine. I'm confused :(.
I think this will not work (and should not) because there is no call to no_transition in a submachine (I don't see it here but I suppose your real code is bigger). The reason is the same as above, no_transition is an error and will assert. But if a submachine cannot process an event, it is not necessarily an error, the outer machine should get its chance to process the event. I'm also afraid you're trying to keep a pointer to the outer machine to process the event (cycle). I suggest pushing the event to a pseudo exit, which will achieve the same a better way.
HTH, Christophe
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