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Two FSM libraries, one interface
by David Bergman 07 Dec '09

07 Dec '09

NO, this is not yet another attempt of mine to irritate people by claiming that the interfaces of Statechart and MSM are similar ;-) When evaluating MSM, both from an interface and performance (read "abuse" ;-)) point of view, I decided to create a common wrapper for both libraries, since I host this awkward notion that the mapping from such a (much more abstract and less verbose) wrapper to the underlying libraries should not vary that much. Be that due to the interfacial commonalities between the two libraries or my great mapping skills :-) Anyway, I just got tired of being a grumpy old passive man, so decided to put some of my money (or time) where my mouth is. I will write more about this side effect of my analysis in a blog post later, as well as provide access to the actual header file. I just want to gauge the interest for such an abstraction layer *for non-complex FSM needs*. I do not claim any commutation, but at least we have a decent sub diagram with arrows from my abstract interface to each one of Statechart and MSM for non-complex cases. I currently imaginatively call this common interface "abstract_fsm.h". It preprocesses a common description to either Statechart or MSM, decided by setting either "USE_SC" or "USE_MSM". It is currently limited to non-nested machines without guards, and only handles the specification, not execution. But, the end result is pretty cool. So, hold on to you LISP hats (there will be parentheses...) and see for yourself. This is a simple FSM app using that abstraction: #include <iostream> #include "abstract_fsm.h" FSM_DEF(Machine, // The type of the FSM (Play)(Stop), // the events // The transitions (including the states) ((Stopped, ((Play, Playing, { std::cout << "starting to play" << std::endl; })) ((Stop, Stopped, { std::cout << "stopping" << std::endl; })))) ((Playing, ((Stop, Stopped, { std::cout << "staying in Stopped" << std::endl; })))) ) int main(int argc, const char* argv[]) { Machine mach; mach.initiate(); mach.process_event(Stop()); mach.process_event(Play()); mach.process_event(Stop()); } Everything is contained in that FSM_DEF construct, including events and transitions (including the source states). One cool thing is that the actions are right there. I have no clue as to the general usability of this abstract layer, but it serves the immediate purpose of testing runtime performance of the two libraries by merely using USE_SC or USE_MSM. This application is preprocessed to this Statechart app (by using -E -DUSE_SC...): #include <boost/statechart/event.hpp> #include <boost/statechart/state_machine.hpp> #include <boost/statechart/simple_state.hpp> #include <boost/statechart/transition.hpp> struct Play : boost::statechart::event<Play> {}; struct Stop : boost::statechart::event<Stop> {}; struct Stopped; struct Playing; struct Machine : boost::statechart::state_machine<Machine, Stopped> { void actStoppedPlayPlaying(const Play& evt) { std::cout << "starting to play" << std::endl; } void actStoppedStopStopped(const Stop& evt) { std::cout << "stopping" << std::endl; } void actPlayingStopStopped(const Stop& evt) { std::cout << "staying in Stopped" << std::endl; } }; struct Stopped : boost::statechart::simple_state<Stopped, Machine> { typedef boost::mpl::list< boost::statechart::transition<Play, Playing, Machine, &Machine::actStoppedPlayPlaying> , boost::statechart::transition<Stop, Stopped, Machine, &Machine::actStoppedStopStopped> > reactions; }; struct Playing : boost::statechart::simple_state<Playing, Machine> { typedef boost::mpl::list< boost::statechart::transition<Stop, Stopped, Machine, &Machine::actPlayingStopStopped> > reactions; }; int main(int argc, const char* argv[]) { Machine mach; mach.initiate(); mach.process_event(Stop()); mach.process_event(Play()); mach.process_event(Stop()); } And when preprocessing to an MSM app (by using -E -DUSE_MSM...): #include <boost/msm/back/state_machine.hpp> #include <boost/msm/front/state_machine_def.hpp> struct Play {}; struct Stop {}; struct Stopped : boost::msm::front::state<> {}; struct Playing : boost::msm::front::state<> {}; struct Machine_ : boost::msm::front::state_machine_def<Machine_> { typedef Stopped initial_state; void actStoppedPlayPlaying(const Play& evt) { std::cout << "starting to play" << std::endl; } void actStoppedStopStopped(const Stop& evt) { std::cout << "stopping" << std::endl; } void actPlayingStopStopped(const Stop& evt) { std::cout << "staying in Stopped" << std::endl; } typedef boost::mpl::vector< a_row<Stopped, Play, Playing, &Machine_::actStoppedPlayPlaying> , a_row<Stopped, Stop, Stopped, &Machine_::actStoppedStopStopped> , a_row<Playing, Stop, Stopped, &Machine_::actPlayingStopStopped> > transition_table; void initiate() {} }; typedef boost::msm::back::state_machine<Machine_> Machine; int main(int argc, const char* argv[]) { Machine mach; mach.initiate(); mach.process_event(Stop()); mach.process_event(Play()); mach.process_event(Stop()); } It is worth noting that once I had wrestled with Boost.Preprocessor and created a mapping to Statechart, the MSM mapping took 14 minutes, and a lot of meta functions were common between the two cases. /David

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Does anyone know what happens to all we write at home?
by Vladimir Batov 07 Dec '09

07 Dec '09

Does anyone know what happens to all we write at home? We habitually put the 'boost' license on such work. However, can your employer claim that *anything* you do belongs to "him" and to slap you with a violation of Confidentiality Agreement or Intellectual Property Agreement? V.

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[rdb, fusion, profile_templates] 0.2.03 - compilation speedup
by Jean-Louis Leroy 06 Dec '09

06 Dec '09

I have uploaded version 0.2.03 to the vault. No new features this time but improvements in compilation speed. The test_odbc project took more than 4.5 minutes to build in debug mode (msvc9, ThinkPad x200s, Intel L9400 with 2 cores @ 1.86 Ghz, 4 Gb RAM) and...17 minutes on a 2Gb RAM computer ! This was becoming unbearable. After a run through profile_templates - thanks to Steven Watanabe for creating this tool ! - I replaced the fusion::maps that were used to gather clause information in sql statement templates with a simpler, less flexible, less orthogonal and less capable version of my own. The result was a 41% speedup (calculated as (old-new)/old) on the 4 Gb computer and 85% on the 2Gb one. The number of template instantiations, as reported by profile_templates, dropped from 86330 to 62771. If someone is interested I can post the complete profiling reports. I plan to focus on datetime support now... Jean-Louis

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Re: [boost] [msm] Review
by Christophe Henry 06 Dec '09

06 Dec '09

Hi David, >>> 2. In Statechart, the definition of a state is coupled to the machine in which it resides >>> while in MSM the state can be defined totally in isolation of the machine, and, thus, reused in other machines >>> 3. In Statechart, the transitions are coupled to the from-state, and defined therein, >>> whereas in MSM, the transitions are coupled to the machine itself; this makes it a bit tricky to reuse a state in Statechart >> >> This is an important interface difference, isn't it? > Yes, which is why I brought it up; see (*) below. Thanks for doing it, I see this as an important point. >* - Yes and no... As I explained in my note to Dave, I did not mean API when I wrote that dreaded sentence about the interface similarity, >I meant it in a more abstract sense. BUT, for simple cases, where we do not deal with transition guards or nested machines, >there actually is a quite close similarity even at a syntactical level. Agreed. But isn't the interface similarity mainly due to the very tightly specified problem domain and to the fact that we all use the excellent MPL tool? Of course, simple state machines using MPL will all look slightly the same, as will do those based on OO-principles with each other. When a new implementation (even based on the same tools) brings important advantages, shouldn't it be considered for inclusion? >They treat guards differently. Yes. I'll come back to it in a minute. >> Let's now add a conflicting transition, which means another possible >> transition on the same event and the same source state, with guards >> deciding which (if any) transition will be taken. >We are now arguably leaving theoretical FSM's and entering pragmatic machines :-) Sure. Theoretical FSM's are anyway about the same for all. My point is to show that differences between MSM and Statechart are subtle but play an important role. >> With MSM you'd have, for example: >> typedef mpl::vector< >> row<State1, Event, State2, &Machine_::action, &Machine_::some_condition>, >> row<State1, Event, State3, &Machine_::action, >> &Machine_::some_other_condition> >> > transition_table; >> >> Could you now write the Statechart version for us? > No ;-) Then, I'm not an expert with Statechart but allow me to try to help ;-) I think (please correct me if I'm wrong) it'd look about like: sc::result react(const Event& evt) { if (some_other_condition(evt)) { action(evt); return transit<State3>();} else if (some_condition(evt) { action(evt); return transit<State2>();} } And this is one important difference, not just a syntactic one. With SC, the structure of the state machine is hidden in the code, which will make your conversion tool harder to write on the direction SC->MSM as the tool will not just be able to parse the code but also understand it. Add a few more actions or other piece of code and I wish your tool luck ;-) OTOH you get more flexibility. So, my point is, there are more differences that syntactic ones, as long as you make more complicated machines. I still agree with you on the point that interfaces are not "widly different" but I put this on the account of a clearly specified problem domain and the fact that most of Boost uses the same MPL tool (due its huge power. Thanks Dave, thanks Aleksey ;-) ). >Yes, there are syntactical differences and decouplings of state vs machine which makes MSM a nicer tool; >and, didi I mention that MSM is in my simple test cases six times faster? You did and I thank you for adding your own tests to the review. As an extra note, if you are ready to give up some state features and need just an enum for the states, you might want to take the FSM in the MPL book. It would probably even be possible to make from it a backend which could at some point partly support the different MSM front-ends. MSM does not yet support this solution in order to deliver a back-end supporting the state features specified by UML (again the restricted problem domain) but it is one of the backends I consider for addition. Do we agree to leave the dreaded sentence behind us and replace it with one saying that both libraries solve the same problem using a wildly different implementation with similarities in the syntax? Christophe

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[chrono] type_traits/common_type and integer/ratio
by Vicente Botet Escriba 06 Dec '09

06 Dec '09

Hi, I'm looking on how to continue with the Boost.Chrono library and I would like to know if * Boost.TypeTraits could take care of the common_type class template. * Boost.Integer could take care of the ratio class template. In this way Boost.Chrono will contain only the time related facilities, duration, time_point and Clocks. In order to minimize the task and been able to purpose as soon as possible the library for review I would like to concentrate on the implementation of the standard proposal and let for a future release the facilities Beman added as * Class template timer, with typedefs: * `system_timer` * `monotonic_timer` * `high_resolution_timer` * Process clocks and timers: * `process_clock`, capturing real, user-CPU, and system-CPU times. * `process_timer`, capturing elapsed real, user-CPU, and system-CPU times. * `run_timer`, convenient reporting of process_timer results. What do you think about this approach? Best, Vicente -- View this message in context: http://old.nabble.com/-chrono--type_traits-common_type-and-integer-ratio-tp… Sent from the Boost - Dev mailing list archive at Nabble.com.

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Re: [boost] [msm] Review
by Christophe Henry 06 Dec '09

06 Dec '09

>> Repeating: the MSM/Statechart overlap in features and interface is quite >> unique to Boost. > > > They definitely overlap in features and also in intent, but my understanding > is that the interfaces are vastly different, and that's an important > distinguishing feature. Am I missing something? No you aren't. At first look, they seem similar, but as soon as you concretely start writing a state machine with both libraries, like Juraj could tell you (he did it), you'll start seeing that the differences are there. Of course, both use states, events and transitions but that's about all. MSM bases itself on the transition table, while with Statechart, the user writes his decisions in the react function. Composites are full state machines with MSM, a simple state with Statechart. MSM uses more metaprogramming, Statechart follows a solution with multiple translation units. Etc. etc. The point is, the interfaces differ, the normal usage even more and the "correct" way to use each (in the authors' eyes) much more as both follow a completely different philosophy, as many heated discussions showed. Christophe

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arithmetic meta functions and traits
by Zachary Turner 06 Dec '09

06 Dec '09

Is there any use for something like this? Following compiles on MSVC 9.0. Despite the simplicity of the final template, it was *NOT* easy to get this working given that there's about 10 ways you should be able to do this according to the standard, but poor SFINAE support makes it next to impossible to get your compiler to accept anything. Since it doesn't do anything highly fancy, I would wager it works on GCC and other compilers as well, although it needs to be tested. struct no_type { }; #define MAKE_BINOP_METAFUNCTIONS(op, binop, traits) \ template<typename T, typename U> no_type operator op (T, U); \ template<typename T, typename U> \ struct traits \ { \ typedef BOOST_TYPEOF(T() op U()) type; \ }; \ template<typename T, typename U> \ struct binop \ { \ private: \ typedef typename traits<T,U>::type result_type; \ public: \ static const bool value = !boost::is_same<result_type,no_type>::value; \ }; MAKE_BINOP_METAFUNCTIONS(+, is_addable, addition_traits); MAKE_BINOP_METAFUNCTIONS(-, is_subtractable, subtraction_traits); MAKE_BINOP_METAFUNCTIONS(/, is_dividable, division_traits); MAKE_BINOP_METAFUNCTIONS(*, is_multipliable, multiplication_traits); Obviously you can define other operators similarly, as well as unary operators. Zach

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Re: [boost] [explore] Library Proposal: Container Streaming
by Brian Wood 06 Dec '09

06 Dec '09

Jeff Flinn writes: > Regardless of the approach taken, I think this would be a useful > facility. I've created a similar, albeit much simplified facility for > two separate projects in the last 5 years. There've been several more > projects that could have used the more general facilities that this lib > offers. I think an on line approach is helpful and we have a service that writes Print functions based on user input -- http://webebenezer.net/cgi-bin/enrobo.cgi. This input: (list<int>) results in this output: void Print(std::ostream& so, const list<int>& abt1) { int indentation = 0; so.fill(' '); so << "\nabt1: "; so << "list has " << abt1.size() << "\n"; indentation += 2; list<int >::const_iterator mediator1 = abt1.begin(); list<int >::const_iterator omega1 = abt1.end(); for (; mediator1 != omega1; ++mediator1) { so.width(indentation); so << " "; so << (*mediator1); so << "\n"; } indentation -= 2; so << std::flush; } Brian Wood http://www.webEbenezer.net <http://www.webebenezer.net/> "The Kingdom of Heaven is like a treasure hidden in the field, which a man found and hid again; and from joy over it he goes and sells all that he has and buys that field."

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MSM Review period extended to Dec 13th
by David Abrahams 06 Dec '09

06 Dec '09

Hi All, We thought this might happen because of the Thanksgiving holiday, and it did: we are extending the review period for the Meta State Machine library until Dec 13th. However, please don't let that delay your review; we'd like to see them all as soon as possible. Msm was written by Christophe Henry, inspired in part by the example in the book "C++ Template Metaprogramming" (http://boostpro.com/mplbook) About the library: Msm (Meta State Machine) is a library allowing the user to easily define high-performance, straightforward and readable UML2 finite state machines, while respecting the principles of efficiency and declarativeness of the original example. To that end, Msm offers several Domain-Specific Embedded Languages that strive to closely emulate a standard UML diagram. Msm supports a broad range of UML features: - state entry/exit - transition actions/guards - composite states - history - orthogonal regions - terminate states - deferred events - explicit entry/fork - entry/exit pseudostates - anonymous transitions - transition conflicts And several non-standard features to make the developer's life easier (interrupt states, query about the current state(s)). Msm (in its current version, 2.0) can be found: * in the sandbox (http://svn.boost.org/svn/boost/sandbox/msm/) * or in the vault: (http://www.boostpro.com/vault/index.php?directory=Msm) Everybody on this list is invited to participate in this formal review. I hope to see your review of Msm, including your vote on acceptance, and I welcome your participation in the ensuing discussions on the Boost developers' mailing list. Please always include in your review a vote as to whether the library should be accepted into Boost. Additionally please consider giving feedback on the following general topics: - What is your evaluation of the design? - What is your evaluation of the implementation? - What is your evaluation of the documentation? - What is your evaluation of the potential usefulness of the library? - Did you try to use the library? - With what compiler? - Did you have any problems? - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? - Are you knowledgeable about the problem domain? -- David Abrahams BoostPro Computing http://boostpro.com

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Regex allocator support
by Fred Sundvik 06 Dec '09

06 Dec '09

Hi, We recently had to use the regular expression library in conditions where there was no available physical memory, for reporting resource consumption when our console game runs out of memory. This wasn't possible however due to the fact that the basic_regex does some dynamic allocations and doesn't provide any allocator specialization, allthough match_results for example does. So we modified the boost code a little bit and added a new template paramter for the allocator, and made constructors that takes allocators as parameters. This was quite straightforward to do, the allocators just had to be passed forward to the all internal classes it uses. The shared_ptr's had to be changed to use the three parameter constructor, that takes a a deleter and allocator, to prevent them from allocating. The mem_block_cache system was a bit more complicated. Initially we disabled it completely, but that obviously wasn't the best solution. So we figured out, that we can use a custom allocator as default, instead of std::allocator. That custom allocator then had to be specialized for the mem_block_nodes, and the funcion calls to get_mem_block replaced by allocator calls. Our implementation isn't ideal, though as we used mem_block_node as the specialization, and to pass the correct size to the allocator, we allocate BOOST_REGEX_BLOCKSIZE / sizeof(mem_block_node) of them, this way it works for allocators that don't specialize for mem_block_node(but only if the size is dividable by sizeof(mem_block_node) ). Better would probably be to make a new type that is BOOST_REGEX_BLOCKSIZE big. We also found another problem with allocation, the match_result::format functions only takes string_type, that isn't specialized by any allocator as they input. This made it impossible to call them with strings using different allocators. So we added specializations of those functions for different allocators and traits. There are probably more functions like that, but since our code doesn't use them there was no need to change anything. So my question is, what are the chances that theese kinds of modificiations gets implemented in the actual library, and possibly in the next c++ standard library as well? I consider it a quite big design flaw to not have any control of the internal allocations, so for me this a quite big thing. Obviously we are doing well with the modifications we made here internally, but there are other applications too that would benefit, many embedded applications for example. Would our code changes be of any use? The changes are only the minimal needed to make it work in our case, and there's many compiler and option permutations not taken care of, so obviously a lot of work would still be needed. Also there's no additional unit tests made. Fred Sundvik Bugbear Entertainment Ltd.

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