Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

Click here to view the latest version of this page.

libs/msm/doc/HTML/examples/TestInternal.cpp

// Copyright 2010 Christophe Henry
// henry UNDERSCORE christophe AT hotmail DOT com
// This is an extended version of the state machine available in the boost::mpl library
// Distributed under the same license as the original.
// Copyright for the original version:
// Copyright 2005 David Abrahams and Aleksey Gurtovoy. Distributed
// under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)

#include <iostream>
#include "boost/mpl/vector/vector30.hpp"

// back-end
#include <boost/msm/back/state_machine.hpp>
//front-end
#include <boost/msm/front/state_machine_def.hpp>
#include <boost/msm/front/functor_row.hpp>
#include <boost/msm/front/internal_row.hpp>

namespace msm = boost::msm;
namespace mpl = boost::mpl;
using namespace msm::front;

namespace
{
    // events
    struct play {};
    struct end_pause {};
    struct stop {};
    struct pause {};
    struct internal_event {};
    struct open_close {};
    struct NextSong {};
    struct PreviousSong {};
    struct to_ignore {};

    // A "complicated" event type that carries some data.
    enum DiskTypeEnum
    {
        DISK_CD=0,
        DISK_DVD=1
    };
    struct cd_detected
    {
        cd_detected(std::string name, DiskTypeEnum diskType)
            : name(name),
            disc_type(diskType)
        {}

        std::string name;
        DiskTypeEnum disc_type;
    };

    // front-end: define the FSM structure 
    struct player_ : public msm::front::state_machine_def<player_>
    {
        // transition actions
        void start_playback(play const&)       { std::cout << "player::start_playback\n"; }
        void open_drawer(open_close const&)    { std::cout << "player::open_drawer\n"; }
        void close_drawer(open_close const&)   { std::cout << "player::close_drawer\n"; }
        void store_cd_info(cd_detected const&) { std::cout << "player::store_cd_info\n"; }
        void stop_playback(stop const&)        { std::cout << "player::stop_playback\n"; }
        void pause_playback(pause const&)      { std::cout << "player::pause_playback\n"; }
        void resume_playback(end_pause const&)      { std::cout << "player::resume_playback\n"; }
        void stop_and_open(open_close const&)  { std::cout << "player::stop_and_open\n"; }
        void stopped_again(stop const&)        {std::cout << "player::stopped_again\n";}
        // guard conditions
        bool good_disk_format(cd_detected const& evt)
        {
            // to test a guard condition, let's say we understand only CDs, not DVD
            if (evt.disc_type != DISK_CD)
            {
                std::cout << "wrong disk, sorry" << std::endl;
                return false;
            }
            return true;
        }
        // transitions internal to Empty
        void internal_action(cd_detected const&){ std::cout << "Empty::internal action\n"; }
        bool internal_guard(cd_detected const&)
        {
            std::cout << "Empty::internal guard\n";
            return false;
        }
        void internal_action(internal_event const&){ std::cout << "Playing::internal action\n"; }
        bool internal_guard(internal_event const&)
        {
            std::cout << "Playing::internal guard\n";
            return false;
        }

        // The list of FSM states
        struct Empty : public msm::front::state<> 
        {
            // every (optional) entry/exit methods get the event passed.
            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 internal_guard_fct 
            {
                template <class EVT,class FSM,class SourceState,class TargetState>
                bool operator()(EVT const& evt ,FSM&,SourceState& ,TargetState& )
                {
                    std::cout << "Empty::internal guard functor\n";
                    return false;
                }
            };
            struct internal_action_fct 
            {
                template <class EVT,class FSM,class SourceState,class TargetState>
                void operator()(EVT const& ,FSM& ,SourceState& ,TargetState& )
                {
                    std::cout << "Empty::internal action functor" << std::endl;
                }
            };
            void internal_action(to_ignore const&)       { std::cout << "Empty::(almost)ignoring event\n"; }
            // Transition table for Empty
            struct internal_transition_table : mpl::vector<
                //    Start     Event         Next      Action                   Guard
                Row  < Empty   , cd_detected , none    , internal_action_fct    ,internal_guard_fct    >,
           Internal  <           cd_detected           , internal_action_fct    ,internal_guard_fct    >,
           a_internal<           to_ignore             , Empty,&Empty::internal_action                 >
                //  +---------+-------------+----------+------------------------+----------------------+
            > {};        
        };
        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_machine_def<Playing_>
        {
            // when playing, the CD is loaded and we are in either pause or playing (duh)
            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;}

            // The list of FSM states
            struct Song1 : public msm::front::state<>
            {
                template <class Event,class FSM>
                void on_entry(Event const&,FSM& ) {std::cout << "starting: First song" << std::endl;}
                template <class Event,class FSM>
                void on_exit(Event const&,FSM& ) {std::cout << "finishing: First Song" << std::endl;}

            };
            struct Song2 : public msm::front::state<>
            { 
                template <class Event,class FSM>
                void on_entry(Event const&,FSM& ) {std::cout << "starting: Second song" << std::endl;}
                template <class Event,class FSM>
                void on_exit(Event const&,FSM& ) {std::cout << "finishing: Second Song" << std::endl;}
            };
            struct Song3 : public msm::front::state<>
            { 
                template <class Event,class FSM>
                void on_entry(Event const&,FSM& ) {std::cout << "starting: Third song" << std::endl;}
                template <class Event,class FSM>
                void on_exit(Event const&,FSM& ) {std::cout << "finishing: Third Song" << std::endl;}
            };
            // the initial state. Must be defined
            typedef Song1 initial_state;
            // transition actions
            void start_next_song(NextSong const&){std::cout << "Playing: start_next_song" << std::endl;}
            void start_prev_song(PreviousSong const&){std::cout << "Playing: start_prev_song" << std::endl;}
            // guard conditions
            struct playing_internal_guard 
            {
                template <class EVT,class FSM,class SourceState,class TargetState>
                bool operator()(EVT const& evt ,FSM&,SourceState& ,TargetState& )
                {
                    std::cout << "Playing::internal guard fct\n";
                    return true;
                }
            };
            struct playing_false_guard 
            {
                template <class EVT,class FSM,class SourceState,class TargetState>
                bool operator()(EVT const& evt ,FSM&,SourceState& ,TargetState& )
                {
                    std::cout << "Playing::false guard\n";
                    return false;
                }
            };
            struct playing_internal_fct 
            {
                template <class EVT,class FSM,class SourceState,class TargetState>
                void operator()(EVT const& evt ,FSM&,SourceState& ,TargetState& )
                {
                    std::cout << "Playing::internal fct\n";
                }
            };
            typedef Playing_ pl; // makes transition table cleaner
            // Transition table for Playing
            struct transition_table : mpl::vector4<
                //      Start     Event          Next      Action                Guard
                //    +---------+---------------+---------+---------------------+----------------------+
                a_row < Song1   , NextSong      , Song2   , &pl::start_next_song                       >,
                a_row < Song2   , PreviousSong  , Song1   , &pl::start_prev_song                       >,
                a_row < Song2   , NextSong      , Song3   , &pl::start_next_song                       >,
                a_row < Song3   , PreviousSong  , Song2   , &pl::start_prev_song                       >
                //    +---------+-------------+---------+---------------------+----------------------+
            > {};
            // Internal transition table for Playing
                //  +---------+----------------+---------+---------------------+-----------------------+
            struct internal_transition_table : mpl::vector<
                // normal internal transition
                //    Start     Event            Next      Action                Guard
             Internal <         internal_event           , playing_internal_fct,playing_internal_guard >,
                // conflict between internal and the external defined above
             Internal <         PreviousSong             , playing_internal_fct,playing_false_guard    >,
             internal <         internal_event           , player_,&player_::internal_action,
                                                           player_,&player_::internal_guard            >
                //  +---------+----------------+---------+---------------------+-----------------------+
            > {};        

            // 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;
            }
        };
        // back-end
        typedef msm::back::state_machine<Playing_> Playing;

        // state not defining any entry or exit
        struct Paused : public msm::front::state<>
        {
        };

        // the initial state of the player SM. Must be defined
        typedef Empty initial_state;

        typedef player_ p; // makes transition table cleaner

        // Transition table for player
        struct transition_table : mpl::vector<
            //    Start     Event         Next      Action               Guard
            //  +---------+-------------+---------+---------------------+----------------------+
          a_row < Stopped , play        , Playing , &p::start_playback                         >,
          a_row < Stopped , open_close  , Open    , &p::open_drawer                            >,
           _row < Stopped , stop        , Stopped                                              >,
            //  +---------+-------------+---------+---------------------+----------------------+
          a_row < Open    , open_close  , Empty   , &p::close_drawer                           >,
            //  +---------+-------------+---------+---------------------+----------------------+
          a_row < Empty   , open_close  , Open    , &p::open_drawer                            >,
          // conflict between a normal and 2 internal transitions (irow/g_irow) 
          // + a state-defined internals defined 2 ways (see Empty)
            row < Empty   , cd_detected , Stopped , &p::store_cd_info   ,&p::good_disk_format  >,
           irow < Empty   , cd_detected ,           &p::internal_action ,&p::internal_guard    >,
         g_irow < Empty   , cd_detected                                 ,&p::internal_guard    >,
            //  +---------+-------------+---------+---------------------+----------------------+
          a_row < Playing , stop        , Stopped , &p::stop_playback                          >,
          a_row < Playing , pause       , Paused  , &p::pause_playback                         >,
          a_row < Playing , open_close  , Open    , &p::stop_and_open                          >,
            //  +---------+-------------+---------+---------------------+----------------------+
          a_row < Paused  , end_pause   , Playing , &p::resume_playback                        >,
          a_row < Paused  , stop        , Stopped , &p::stop_playback                          >,
          a_row < Paused  , open_close  , Open    , &p::stop_and_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;
        }
    };
    // Pick a back-end
    typedef msm::back::state_machine<player_> player;

    //
    // Testing utilities.
    //
    static char const* const state_names[] = { "Stopped", "Open", "Empty", "Playing", "Paused" };
    void pstate(player const& p)
    {
        std::cout << " -> " << state_names[p.current_state()[0]] << std::endl;
    }

    void test()
    {        
        player p;
        // needed to start the highest-level SM. This will call on_entry and mark the start of the SM
        p.start(); 
        // this event will be ignored and not call no_transition
        p.process_event(to_ignore());
        // go to Open, call on_exit on Empty, then action, then on_entry on Open
        p.process_event(open_close()); pstate(p);
        p.process_event(open_close()); pstate(p);
        // will be rejected, wrong disk type
        p.process_event(
            cd_detected("louie, louie",DISK_DVD)); pstate(p);
        p.process_event(
            cd_detected("louie, louie",DISK_CD)); pstate(p);
        p.process_event(play());
        p.process_event(NextSong());
        std::cout << "sending an internal event" << std::endl;
        p.process_event(internal_event());
        std::cout << "conflict between the internal and normal transition. Internal is tried last" << std::endl;
        p.process_event(PreviousSong());

        // at this point, Play is active      
        p.process_event(pause()); pstate(p);
        // go back to Playing
        p.process_event(end_pause());  pstate(p);
        p.process_event(pause()); pstate(p);
        p.process_event(stop());  pstate(p);
        // event leading to the same state
        // no action method called as it is not present in the transition table
        p.process_event(stop());  pstate(p);
    }
}

int main()
{
    test();
    return 0;
}