C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  State machine framework with dynamic configurability          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Dave Guest Posted: Thu Jun 23, 2005 11:12 pm    Post subject: State machine framework with dynamic configurability Hi all, I'm working on a project to improving a legacy software on Unix which has a flat state machine with hundreds of states in it. I'm looking for a state machine framework that supports nested states, guards, entry, exit and preferrably other state machine features such as concurrent state transitions, orthorgonal states, shallow/deep histories. Another requirement is that the state machine framework should be dynamically configurable, say in my main program I have 3 states, and i can build a shared object which defines a state machine as a sub-state machine for one of the states in the main program. All these should be achieved without recompiling the main program. I looked into the boost statechart library and dug up the thread that Andreas Huber started when the idea to create boost statechart was first hatched. The only problem is that the library wasn't designed with dynamic configurability in mind, so it doesn't suit my needs. I also looked into the quantum platform, etc framework, but I have trouble finding documentation (perhaps I need to buy the book?) I've also tried a statechart modelling tool called SmartState and used it to generate a state machine but the state machine features supported are limited and I have some reservations about the design of the state machine framework that the tool generates So.. my question is: is there any other state machine framework that is dynamically configurable and support the most of the state machine features mentioned above? any help is welcome, thanks in advance newbie [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Cyril Guest Posted: Fri Jun 24, 2005 3:35 pm    Post subject: Re: State machine framework with dynamic configurability I know I'm not answering to your question. Anyway, I think you should have a look at: http://www.codeproject.com/ce/dev_embed_statemachine.asp Sincerely, Cyril [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Andreas Huber Guest Posted: Wed Jul 06, 2005 9:59 am    Post subject: Re: State machine framework with dynamic configurability Hi Dave Sorry for the late reply, I was on holiday. Dave wrote: [snip] Quote: Another requirement is that the state machine framework should be dynamically configurable, say in my main program I have 3 states, and i can build a shared object which defines a state machine as a sub-state machine for one of the states in the main program. All these should be achieved without recompiling the main program. A very limited form of dynamic configurability is possible with Boost.Statechart: You can implement the main FSM in the main exe and to customize by dynamically loading dlls. Of course, for this to work you'd need to know the points of customization beforehand. A related FAQ item can be found here: http://tinyurl.com/ak239 Quote: I looked into the boost statechart library and dug up the thread that Andreas Huber started when the idea to create boost statechart was first hatched. The only problem is that the library wasn't designed with dynamic configurability in mind, so it doesn't suit my needs. Out of curiosity: Would you care to describe what kind of application you need such a library for? When I researched the requirements for Boost.Statechart I came to the conclusion that *full* dynamic configurability is needed only *very* rarely in conjunction with the full FSM feature set. One good example of such an app would be a program that allows people to design an FSM and study its behavior graphically, e.g. for educational purposes. [snip] Quote: So.. my question is: is there any other state machine framework that is dynamically configurable and support the most of the state machine features mentioned above? FWIW, I've had a look at quite a few freely available FSM libraries. None of them does even come close to satisfying your requirements. I can't say whether any of the commercial products do what you want. Regards, -- Andreas Huber When replying by private email, please remove the words spam and trap from the address shown in the header. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top borg@swirve.com Guest Posted: Wed Jul 06, 2005 1:29 pm    Post subject: Re: State machine framework with dynamic configurability Hi Andreas, I was also considering a dynamic FSM as part of a mini interpreted language implemented using the Boost.Spirit framework. The language would allow users to specify states and state transitions as part of the scripting language that would subsequently run in a small VM. I haven't started yet, but was also wondering if I could use the Boost statechart library in any way. Regards, Adrian [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Dave Guest Posted: Wed Jul 06, 2005 10:07 pm    Post subject: Re: State machine framework with dynamic configurability Thanks but I have trouble accessing the link... [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Dave Guest Posted: Wed Jul 06, 2005 10:31 pm    Post subject: Re: State machine framework with dynamic configurability the FAQ illustrates how to modify the existing layout of an FSM, but I doubt whether it would be possible to implement the main FSM in the main exe and then dynamically load dlls to add inner/sub-states to existing states; since the state transition/reactions have to be specified as template parameters. Quote: Out of curiosity: Would you care to describe what kind of application you need such a library for? This is probably off-topic for this ng but I'll provide my reasons so you can decide if they're reasonable or not. The application I mentioned original post is a call control application, in fact several of them. (Naturally each application is maintained by a group of developers) Each of the applications has a flat Fsm with many states. My goal is to design a framework that has a main Fsm that is common to all the call control applications (with points of customization pre-defined) and then dynamically load DLLs to customize the behavior (by adding inner/sub-states) of the Fsm. The obvious advantage of doing so would be code reuse. Another reason to do so is that if a customization for a specific customer is needed (say add a few states to the fsm), only a few DLLs need to be modified/added, whereas in the existing design the main application has to be modified and recompiled. In this way the customization may be done by a developer who does not have full access to the source code/statechart, all he/she needs to know is the interface of the "point of customization". Dynamic configurabliity aside, the application I'm working on is a call control application, so I only need one instance of the state machine, one instance of each state and use context objects to store state information for each call. When I skimmed through the statechart tutorial I see that the "Entry" and "Exit" functions are implemented using the constructor and destructor of the simple_state class, so I suppose that each state object is constructed when entered and destructed when exited. I'm not sure.. if a state is entered and exited repeatedly, say in the stopwatch example, whether the object construction/destruction incurs an unecessary cost. If I'm wrong, please correct me. If there's a free Fsm libary (not licensed under GPL) that satisfies my requirements that would be great, but I would also consider commercial products. Yet I'm under the impression that commerial Fsm libaries usually come with graphical UML editors... right now I'm stuck with Rational Rose 98 (old version), so the new tool would have to be able to import UML diagrams drawn using Rational Rose 98. One good thing about Rational Rose is that the saved files are pretty human readable so I can just write a script to parse the state chart specifications and generate code that uses some Fsm libarary (say boost statechart). Of course another alternative would be rely on the UML editor to generate frameowrk code for me but I would still have to make some modifications to archive dynamic configurability. thanks Dave - I'm a novice please be nice :-) [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Andreas Huber Guest Posted: Wed Jul 06, 2005 10:32 pm    Post subject: Re: State machine framework with dynamic configurability Hi Adrian Quote: I was also considering a dynamic FSM as part of a mini interpreted language implemented using the Boost.Spirit framework. The language would allow users to specify states and state transitions as part of the scripting language that would subsequently run in a small VM. I haven't started yet, but was also wondering if I could use the Boost statechart library in any way. Unlikely, given that "interpreted" is a firm requirement (otherwise you could have your program generate C++ code, compile it and run the resulting exe). IOW, as soon as the statechart layout is fully variable depending on user input, you absolutely need full dynamic configurability. This is not supported by Boost.Statechart. Regards, -- Andreas Huber When replying by private email, please remove the words spam and trap from the address shown in the header. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Andreas Huber Guest Posted: Fri Jul 08, 2005 1:06 am    Post subject: Re: State machine framework with dynamic configurability The answer to this post is rather OT for this newsgroup as it discusses the properties of a library instead of general C++. The answer has therefore been posted to the much more appropriate boost user group: http://thread.gmane.org/gmane.comp.lib.boost.user/11953 -- Andreas Huber When replying by private email, please remove the words spam and trap from the address shown in the header. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Alan Chen Guest Posted: Fri Jul 08, 2005 1:15 am    Post subject: Re: State machine framework with dynamic configurability Did you see the message on that thread that mentions the Boost Graph library. I think the BGL would handle your dynamic requirement quite well; as well as your guard, entry, exit conditions, and nested states reasonably well. However, it would take a little work to implement concurrent, orthogonal state transitions... [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Dave Guest Posted: Thu Jul 14, 2005 5:35 pm    Post subject: Re: State machine framework with dynamic configurability I agree that the thread is rather OT for this newsgroup now.. but I've been unable to post follow-ups to that boost user group, I got rejected saying I'm not authorized to post to that list and I've tried multiple times with different email addresses. Hence I'll post my follow-up here so the discussion could continue. Quote: Why do you think that the transition/reaction specification interface is a problem? The FAQ item shows that you can have a base FSM that uses a virtual function to delay the decision where to transit from a given state (Idle) when a specific event occurs (EvStart). The base FSM (PumpBase) would be compiled into the main exe. If you want to modify the behavior in a dll, all you need to do is to derive from the base FSM and inside the virtual function override you transit to the desired state. Of course, for all this to work the main exe would need to have a means of constructing an object of the derived class (MyPump) that was loaded from the dll. This is easy enough to do with a factory. You're right, it's possible to do so. I have yet to spend more time on writing test programs but right now I see some limitations. Say for the PumpBase example, the designer of the main Fsm decides to allow customization for the Idle state and Running state. In the example illustrated in the FAQ a MyRunning state (and inner states added to it) is defined and the MyPump Fsm derives from PumpBase to specify a state transition to the new MyRunning state. Suppose now I want to add some inner states for the Idle state. I can define a new MyIdle state but I cannot make it the initial state of MyPump since Idle was specified as a template parameter in PumpBase and MyPump derives from PumpBase. Let's put that aside and now let's suppose there's a third state in PumpBase Fsm: Stopped, and a state transition from Running to Stopped is triggered by event EvStop. and the following "point of customization" is defined in PumpBase virtual sc::result react(Running& running, const EvStop &) const; To add inner states to Stopped I can define MyStopped and have MyPump transition from Running to MyStopped. However in MyPump Running is replaced by MyRunning, so I need to have my own react method to transit to MyStopped, and I'm not even using the "point of customization" in PumpBase because it has a different signature. Up till now it looks like I'm defining a new Fsm to replace PumpBase rather than customizing it. All this is fine if PumpBase has few states. Yet consider the case when 2 developers work on PumpBase, one responsible for customizing the Running state, the other for customizing the Stopped state. The developers should be able to work on the state machine without knowing each other. Yet as I've illustrated above, there can only be one MyPump class and whoever writes that class has to be aware of the MyRunning and MyStopped class and write the react functions accordingly. btw, I think there's a typo in the FAQ code snippet. "sc::custom_reaction< EvStart >" should not be the third template argument for struct Idle. Quote: Maybe there's just a terminology misunderstanding but I don't see the benefit of the context object. In fact, the use of a context object here looks like a common antipattern, a "winnebago" object (stolen from Jeff Garland). You'll find more on this here (search for the first occurrence of "heuristic" and read what follows): http://lists.boost.org/MailArchives/boost/msg79540.php Yes the term is confusing since context has a different meaning in boost statechart, maybe I could call it a session object. Yes it is an antipattern if the object requires modification everytime a new field is needed, but with a property map the new field can simply be inserted into the map. Moreover, since a state class is destroyed after a state is exited, any state information stored within that state is lost. Information that needs to persist throughout the execution of the state machine has to be stored in the state machine class, which in effect becomes the winnebago object. thanks Dave [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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