Re: [boost] [msm] guard behavior if guard guards the transition MSM threats event as handled is that correct ?

Subject: Re: [boost] [msm] guard behavior if guard guards the transition MSM threats event as handled is that correct ?
From: Richard Szabo (sz.richard_at_[hidden])
Date: 2011-11-25 10:31:12

Hi Christophe

Bad news I have tried to add an internal event table to my state base
class that it is forwards the event to the outer one if the state
machine where the state is used is a sub state machine.

I have added a line something like this :

        struct internal_transition_table : boost::mpl::vector<
          //        Event       Action             Guard
          //       +-----------+------------------+---------------+
  bMsmFr::Internal < BaseEvent , IntFwdToOuterFct , bMsmFr::none >
          //       +-----------+------------------+---------------+
        > {};

IntFwdToOuterFct  check when ever the event can be forwarded to an
outer state machine ( is there an outer state machine ) and if there
is one it calls the interface function to process it.
if there is none that prints a warning that the event is not handled
in this state.

before this change when I compiled the same state machine the compiler
was using up 1.7 GB heap to compile this particular CPP file.
Whit the change above I get a following error and a crash in a
compiler when the heap usage reaches 4.2 GB

\boost/mpl/for_each.hpp(69) : fatal error C1060: compiler is out of heap space

I was using VC9 64bit version on win7 64bit with 12G memory ......

So by adding the internal transition table makes compiler heap usage
to grow  around  by 300 %

So I can not compile such a code....

Cheers
Richie
On 25 November 2011 02:54, Richard Szabo <sz.richard_at_[hidden]> wrote:
> Hi Christophe
>
>> Sure. I see other ways out of your problem. I think they are elegant and
>> conform to the spirit of state machines:
>> - exit points, as previously said. Just write another region as last, which
>> will process your event and send it out to the outer. This has the
>> disadvantage to force you to check is the event has been processed or not.
>> - internal transitions in the submachine itself. IIUC, SubRunning is meant
>> to be a submachine, right? Then we only need to add this to its definition:
>>
>> struct internal_transition_table : mpl::vector<
>>            Internal <   event3  , Action , Guard >
>>           > {};
>>
>>
>> (supposing you need a guard, this is optional).
>> What does this mean? We added to your submachine (or substate) an internal
>> transition table. By convention, MSM decides this is less "inner" than a
>> standard transition table, so the transition table is tried first. If no
>> transition from the transition table processes the event (or if the event is
>> rejected by guards), then the internal table is tried.
>> This can be easily used to replace your use of no_transition, it is more
>> elegant, Standard-conforming and you have extra capabilities (like having
>> different handlers, conflicting ones solved by guards, etc). I find this
>> quite fun :)
>>
>
> Great Great Great .... you are always 1 step a head of me ....
> Yes this sunds a nice solution and even I can hide the internal
> transition table in ta sub state machine running base state all states
> creating sub states are just can use this base state ....
> This is cool I hope internal_transition_table allows to use baseEvents
> as well like outer ones ...
>
>
>> The whole internal transitions have been rewritten in 1.48 to allow this to
>> work for all machines so you will need it or trunk (sadly this also means
>> that while I tested as well as I could, I cannot exclude the possibility of
>> a bug).
>
> Don't worry I will come back to you if it is buggy ... I think with
> our virtual test system we will find problems quick if there any ...
>
>
> Thanks for the support
>
> Cheers
> Richie
>
> On 24 November 2011 22:21, Christophe Henry
> <christophe.j.henry_at_[hidden]> wrote:
>>> 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 ...
>>
>> Sorry, I should have been more explicit (and avid sheating to save a guard).
>> You need to invert your 2 transitions to get the desired effect (processing
>> is done from the bottom of the table):
>>
>>       Row < SubRunning , baseEvent , none       , ProcessBaseEvent ,
>> FwdGuard >,
>>       Row < SubRunning , event3    , none       , LogDefer         , none >
>>
>> Now, deferring has a higher priority, which gives the following desired
>> output:
>>
>> 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
>> MS1 DEFERED: event3 // ok, defer event3
>> FwdGuard: returns:0, event: event4 //event4 is not deferred
>> MS1 DEFERED: event3 // event4 processed, can we process event3? Nope, defer
>> again
>> FwdGuard: returns:0, event: event5
>> MS1 Leaving State: SubRunning by: event5
>> MS1 Entering State: AfterSub by: event5 // we changed state, can we process
>> event3?
>> MS1 no_transition event (event3) // yes but we have no transition, call
>> handler
>>
>>
>>> 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.
>>
>> State machines have a long history in the hardware world. And there it is
>> tradition that if no transition processes an event, it is an error. Purists
>> spend a lot of time handling every event in every state and even have state
>> tables to check this.
>> This means that to be completely correct, we should write an internal
>> transition in every state for every event to document we choose to ignore
>> these events (I try to do it regularly and it does help me from time to
>> time).
>> The UML Standard kept all this. When a transition could handle the event but
>> rejects it, the event is processed. For once the Standard is about clear...
>> ;-)
>> But there are solutions to your problem in MSM's toolbox.
>>
>>> 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.
>>
>> Admittedly. We'll have to be patient.
>>
>>> 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 :).
>>
>> I personally use callbacks with boost::function or signals to avoid cycles
>> but yes, it is still a logical cycle.
>>
>>> 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 ....
>>
>> Sure. I see other ways out of your problem. I think they are elegant and
>> conform to the spirit of state machines:
>> - exit points, as previously said. Just write another region as last, which
>> will process your event and send it out to the outer. This has the
>> disadvantage to force you to check is the event has been processed or not.
>> - internal transitions in the submachine itself. IIUC, SubRunning is meant
>> to be a submachine, right? Then we only need to add this to its definition:
>>
>> struct internal_transition_table : mpl::vector<
>>            Internal <   event3  , Action , Guard >
>>           > {};
>>
>>
>> (supposing you need a guard, this is optional).
>> What does this mean? We added to your submachine (or substate) an internal
>> transition table. By convention, MSM decides this is less "inner" than a
>> standard transition table, so the transition table is tried first. If no
>> transition from the transition table processes the event (or if the event is
>> rejected by guards), then the internal table is tried.
>> This can be easily used to replace your use of no_transition, it is more
>> elegant, Standard-conforming and you have extra capabilities (like having
>> different handlers, conflicting ones solved by guards, etc). I find this
>> quite fun :)
>>
>> The whole internal transitions have been rewritten in 1.48 to allow this to
>> work for all machines so you will need it or trunk (sadly this also means
>> that while I tested as well as I could, I cannot exclude the possibility of
>> a bug).
>>
>> HTH,
>> Christophe
>>
>>
>>
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