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Compare

On this page, we have implemented the same state machine (the "simple" sample from boost::msm) with various statemachine libraries.

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  • boost::msm
  • boost::statechart
  • instantFSM

boost::msm

// events
    struct play {};
    struct end_pause {};
    struct stop {};
    struct pause {};
    struct open_close {};
    struct cd_detected{};

    // Concrete FSM implementation 
    struct player_ : public msm::front::state_machine_def<player_>
    {
        // no need for exception handling or message queue
        typedef int no_exception_thrown;
        typedef int no_message_queue;

        // The list of FSM states
        struct Empty : public msm::front::state<> 
        {
            // optional entry/exit methods
            template <class Event,class FSM>
            void on_entry(Event const&,FSM& ) {/*std::cout << "entering: Empty" << std::endl;*/}
            template <class Event,class FSM>
            void on_exit(Event const&,FSM& ) {/*std::cout << "leaving: Empty" << std::endl;*/}
        };
        struct Open : public msm::front::state<> 
        { 
            template <class Event,class FSM>
            void on_entry(Event const&,FSM& ) {/*std::cout << "entering: Open" << std::endl;*/}
            template <class Event,class FSM>
            void on_exit(Event const&,FSM& ) {/*std::cout << "leaving: Open" << std::endl;*/}
        };

        struct Stopped : public msm::front::state<> 
        { 
            template <class Event,class FSM>
            void on_entry(Event const&,FSM& ) {/*std::cout << "entering: Stopped" << std::endl;*/}
            template <class Event,class FSM>
            void on_exit(Event const&,FSM& ) {/*std::cout << "leaving: Stopped" << std::endl;*/}
        };

        struct Playing : public msm::front::state<>
        {
            template <class Event,class FSM>
            void on_entry(Event const&,FSM& ) {/*std::cout << "entering: Playing" << std::endl;*/}
            template <class Event,class FSM>
            void on_exit(Event const&,FSM& ) {/*std::cout << "leaving: Playing" << std::endl;*/}
        };

        struct Paused : public msm::front::state<>
        {
            template <class Event,class FSM>
            void on_entry(Event const&,FSM& ) {/*std::cout << "entering: Paused" << std::endl;*/}
            template <class Event,class FSM>
            void on_exit(Event const&,FSM& ) {/*std::cout << "leaving: Paused" << std::endl;*/}
        };

        // the initial state of the player SM. Must be defined
        typedef Empty initial_state;
        // transition actions
        void start_playback(play const&)       {  }
        void open_drawer(open_close const&)    {  }
        void close_drawer(open_close const&)   {  }
        void store_cd_info(cd_detected const& cd) { }
        void stop_playback(stop const&)        {  }
        void pause_playback(pause const&)      { }
        void resume_playback(end_pause const&)      {  }
        void stop_and_open(open_close const&)  {  }
        void stopped_again(stop const&){}
        // guard conditions

        typedef player_ p; // makes transition table cleaner

        // Transition table for player
        struct transition_table : mpl::vector<
            //    Start     Event         Next      Action                 Guard
            //    +---------+-------------+---------+---------------------+----------------------+
              _row < Stopped , play        , Playing                      >,
              _row < Stopped , open_close  , Open                             >,
              _row < Stopped , stop        , Stopped                         >,
            //    +---------+-------------+---------+---------------------+----------------------+
              _row < Open    , open_close  , Empty                            >,
            //    +---------+-------------+---------+---------------------+----------------------+
              _row < Empty   , open_close  , Open                              >,
              _row < Empty   , cd_detected , Stopped                         >,
            //    +---------+-------------+---------+---------------------+----------------------+
              _row < Playing , stop        , Stopped                         >,
              _row < Playing , pause       , Paused                         >,
              _row < Playing , open_close  , Open                            >,
            //    +---------+-------------+---------+---------------------+----------------------+
              _row < Paused  , end_pause   , Playing                      >,
              _row < Paused  , stop        , Stopped                         >,
              _row < Paused  , open_close  , Open                            >
            //    +---------+-------------+---------+---------------------+----------------------+
        > {};

        // Replaces the default no-transition response.
        template <class FSM,class Event>
        void no_transition(Event const& e, FSM&,int state)
        {
            std::cout << "no transition from state " << state
                << " on event " << typeid(e).name() << std::endl;
        }
    };
    typedef msm::back::state_machine<player_> player;

boost::statechart

//events
    struct play : sc::event< play > {};
    struct end_pause : sc::event< end_pause > {};
    struct stop : sc::event< stop > {};
    struct pause : sc::event< pause > {};
    struct open_close : sc::event< open_close > {};
    struct cd_detected : sc::event< cd_detected > {};

    struct Empty;
    struct Open;
    struct Stopped;
    struct Playing;
    struct Paused;
    // SM
    struct player : sc::state_machine< player, Empty > 
    {
        void open_drawer(open_close const&)         { /*std::cout << "player::open_drawer\n";*/ }
        void store_cd_info(cd_detected const& cd)   {/*std::cout << "player::store_cd_info\n";*/ }
        void close_drawer(open_close const&)        { /*std::cout << "player::close_drawer\n";*/ }
        void start_playback(play const&)            { /*std::cout << "player::start_playback\n";*/ }
        void stopped_again(stop const&)             {/*std::cout << "player::stopped_again\n";*/}
        void stop_playback(stop const&)             { /*std::cout << "player::stop_playback\n";*/ }
        void pause_playback(pause const&)           { /*std::cout << "player::pause_playback\n"; */}
        void stop_and_open(open_close const&)       { /*std::cout << "player::stop_and_open\n";*/ }
        void resume_playback(end_pause const&)      { /*std::cout << "player::resume_playback\n";*/ }
    };

    struct Empty : sc::simple_state< Empty, player >
    {
        Empty() { /*std::cout << "entering Empty" << std::endl;*/ } // entry
        ~Empty() { /*std::cout << "leaving Empty" << std::endl;*/ } // exit
        typedef mpl::list<
            sc::transition< open_close, Open,
            player, &player::open_drawer >,
            sc::transition< cd_detected, Stopped,
            player, &player::store_cd_info > > reactions;

    };
    struct Open : sc::simple_state< Open, player >
    {
        Open() { /*std::cout << "entering Open" << std::endl;*/ } // entry
        ~Open() { /*std::cout << "leaving Open" << std::endl;*/ } // exit
        typedef sc::transition< open_close, Empty,
            player, &player::close_drawer > reactions;

    };
    struct Stopped : sc::simple_state< Stopped, player >
    {
        Stopped() { /*std::cout << "entering Stopped" << std::endl;*/ } // entry
        ~Stopped() { /*std::cout << "leaving Stopped" << std::endl;*/ } // exit
        typedef mpl::list<
            sc::transition< play, Playing,
            player, &player::start_playback >,
            sc::transition< open_close, Open,
            player, &player::open_drawer >, 
            sc::transition< stop, Stopped,
            player, &player::stopped_again > > reactions;

    };
    struct Playing : sc::simple_state< Playing, player >
    {
        Playing() { /*std::cout << "entering Playing" << std::endl;*/ } // entry
        ~Playing() { /*std::cout << "leaving Playing" << std::endl;*/ } // exit
        typedef mpl::list<
            sc::transition< stop, Stopped,
            player, &player::stop_playback >,
            sc::transition< pause, Paused,
            player, &player::pause_playback >, 
            sc::transition< open_close, Open,
            player, &player::stop_and_open > > reactions;
    };
    struct Paused : sc::simple_state< Paused, player >
    {
        Paused() { /*std::cout << "entering Paused" << std::endl;*/ } // entry
        ~Paused() { /*std::cout << "leaving Paused" << std::endl;*/ } // exit
        typedef mpl::list<
            sc::transition< end_pause, Playing,
            player, &player::resume_playback >,
            sc::transition< stop, Stopped,
            player, &player::stop_playback >, 
            sc::transition< open_close, Open,
            player, &player::stop_and_open > > reactions;
    };

instantFSM

StateMachine sm(
    State("Empty", initialTag,
      OnEntry([](){/*std::cout << "entering: Empty" << std::endl;*/}),
      OnExit([](){/*std::cout << "leaving: Empty" << std::endl;*/}),
      Transition( OnEvent("open_close"), Target("Open")),
      Transition( OnEvent("cd_detected"),Target("Stopped"))
    ),
    State("Open",
      OnEntry([](){/*std::cout << "entering: Open" << std::endl;*/}),
      OnExit([](){/*std::cout << "leaving: Open" << std::endl;*/}),
      Transition( OnEvent("open_close"), Target("Empty"))
    ),
    State("Stopped",
      OnEntry([](){/*std::cout << "entering: Stopped" << std::endl;*/}),
      OnExit([](){/*std::cout << "leaving: Stopped" << std::endl;*/}),
      Transition( OnEvent("play"),       Target("Playing")),
      Transition( OnEvent("open_close"), Target("Open")),
      Transition( OnEvent("stop"),       Target("Stopped"))
    ),
    State("Playing",
      OnEntry([](){/*std::cout << "entering: Playing" << std::endl;*/}),
      OnExit([](){/*std::cout << "leaving: Playing" << std::endl;*/}),
      Transition( OnEvent("stop"),       Target("Stopped")),
      Transition( OnEvent("pause"),      Target("Paused")),
      Transition( OnEvent("open_close"), Target("Open"))
    ),
    State("Paused",
      OnEntry([](){/*std::cout << "entering: Paused" << std::endl;*/}),
      OnExit([](){/*std::cout << "leaving: Paused" << std::endl;*/}),
      Transition( OnEvent("stop"),       Target("Stopped")),
      Transition( OnEvent("end_pause"),  Target("Playing")),
      Transition( OnEvent("open_close"), Target("Open"))
    )

  );