Boost.MSM：通过连接伪状态退出正交区域

Question

我打算将 boost.msm 与包含 正交区域 的 composite 概念一起使用。我想在退出时同步所有正交区域。换句话说：当且仅当所有区域都达到其最后一个状态时，我的复合之后的状态才会被激活。

UML 2.4 "Superstructure" 提出 join 伪状态（即第 15.3.8 章）。在 boost 中，有一个 fork，但我找不到其对应连接的任何实现。

boost.msm中没有join伪状态吗？我如何将加入伪状态的概念与 boost.msm 一起应用？

Answer 1

您可以使用每次进入连接状态时都会递增的计数器。当此计数器等于正交区域的数量时，将激活加入状态之后的状态。

这可以手动或以通用方式完成。 下面我实现了一种通用方式，通过从模板JoinSM 继承将连接逻辑添加到子机Sub。

Sub 有 3 个正交区域（在这个简单的示例中，每个区域仅包含一个状态，即 Orthogonal1、Orthogonal2 和 Orthogonal3）。所有这些正交状态都连接到Join 状态，但在Sub 中没有指定从Join 状态直接连接到Exit 状态。

此连接在JoinSM 中实现。每次从Sub 到达Join 状态时，都会激活Waiting 状态并且计数器递增。如果计数器达到正交区域的数量，则触发事件AllJoined 并激活到Exit 的转换。

由于JoinSM通过initial_state的大小查询正交区域的数量，在Sub中添加或删除区域将自动反映在连接逻辑中。

#include <iostream>
#include <cstdlib>
#include <memory>
#include <cxxabi.h>

template <class T>
std::string demangle()
{
    const char* name = typeid(T).name();
    int status = -1; 
    std::unique_ptr<char, void(*)(void*)> res {
        abi::__cxa_demangle(name, NULL, NULL, &status),
        std::free
    };
    return (status==0) ? res.get() : name ;
}


#include <boost/msm/back/state_machine.hpp>
#include <boost/msm/front/state_machine_def.hpp>
#include <boost/msm/front/functor_row.hpp>
#include <boost/msm/back/metafunctions.hpp>
#include <boost/mpl/assert.hpp>

using namespace boost::msm;
using namespace boost::msm::front;


template <typename State>
struct BaseState : public boost::msm::front::state<>
{
    template <class Event,class FSM> void on_entry(Event const&,FSM& )
    {
        std::cout << "on_entry: " << demangle<State>()  << std::endl;
    }
    template <class Event,class FSM> void on_exit(Event const&,FSM& ) 
    {
        std::cout << "on_exit: " << demangle<State>() << std::endl;
    }
};


// EVENTS
struct EnterOrthogonal {};

struct Orthogonal1Finished{};
struct Orthogonal2Finished{};
struct Orthogonal3Finished{};



struct SubSM_ : state_machine_def<SubSM_>
{
    struct Started : BaseState<Started>{};
    struct Exit : exit_pseudo_state<none> {};

    struct Orthogonal1 : BaseState<Orthogonal1>{};
    struct Orthogonal2 : BaseState<Orthogonal2>{};
    struct Orthogonal3 : BaseState<Orthogonal3>{};

    struct Join : BaseState<Join>{};

    typedef boost::mpl::vector<Orthogonal1, Orthogonal2, Orthogonal3> initial_state;
    struct transition_table : boost::mpl::vector<
     Row<Orthogonal1, Orthogonal1Finished, Join, none, none>,
     Row<Orthogonal2, Orthogonal2Finished, Join, none, none>,
     Row<Orthogonal3, Orthogonal3Finished, Join, none, none>
     > {};
};


template <typename SM, typename JoinState = typename SM::Join, typename ExitState = typename SM::Exit>
struct JoinSM  : SM
{
    struct AllJoined{};

    constexpr static int num_regions = boost::mpl::size<typename SM::initial_state>::value;
    int count;

    template <class Event,class FSM>
    void on_entry(Event const& ,FSM&) 
    {
        // reset count
        count = 0;
    }

    struct Waiting : BaseState<Waiting>
    {
        template <class Event,class FSM>
        void on_entry(const Event& e,FSM& f)
        {
            BaseState<Waiting>::on_entry(e,f);
            f.count++; 
            if (f.count == FSM::num_regions)
            {
                f.process_event(AllJoined()); 
            } 
        }
    };

    typedef boost::mpl::vector<
        Row<JoinState, none, Waiting, none, none>,
        Row<Waiting, AllJoined, ExitState, none, none>
    > additional_transition_table;

    typedef boost::mpl::joint_view<
        typename SM::transition_table,
        additional_transition_table
    > transition_table;
};

// inherit from JoinSM to add the joining logic
using Sub = back::state_machine<JoinSM<SubSM_>>;

struct MainSM_ : state_machine_def<MainSM_>
{
    struct Started : BaseState<Started>{};
    struct AfterJoin : BaseState<AfterJoin>{};
    using initial_state = boost::mpl::vector<Started>;
    struct transition_table : boost::mpl::vector<
        Row<Started, EnterOrthogonal, Sub, none, none>,
        Row<Sub::exit_pt<SubSM_::Exit>, none, AfterJoin, none, none>
    > {};
};

struct MainSM_;
using Main = back::state_machine<MainSM_>;    


int main()
{

    Main main;
    main.start();
    main.process_event(EnterOrthogonal());
    main.process_event(Orthogonal3Finished());
    main.process_event(Orthogonal1Finished());
    main.process_event(Orthogonal2Finished());
}

输出：

on_entry: MainSM_::Started
on_exit: MainSM_::Started
on_entry: SubSM_::Orthogonal1
on_entry: SubSM_::Orthogonal2
on_entry: SubSM_::Orthogonal3
on_exit: SubSM_::Orthogonal3
on_entry: SubSM_::Join
on_exit: SubSM_::Join
on_entry: JoinSM<SubSM_, SubSM_::Join, SubSM_::Exit>::Waiting
on_exit: SubSM_::Orthogonal1
on_entry: SubSM_::Join
on_exit: SubSM_::Join
on_entry: JoinSM<SubSM_, SubSM_::Join, SubSM_::Exit>::Waiting
on_exit: SubSM_::Orthogonal2
on_entry: SubSM_::Join
on_exit: SubSM_::Join
on_entry: JoinSM<SubSM_, SubSM_::Join, SubSM_::Exit>::Waiting
on_exit: JoinSM<SubSM_, SubSM_::Join, SubSM_::Exit>::Waiting
on_exit: JoinSM<SubSM_, SubSM_::Join, SubSM_::Exit>::Waiting
on_exit: JoinSM<SubSM_, SubSM_::Join, SubSM_::Exit>::Waiting
on_entry: MainSM_::AfterJoin

现场示例： http://coliru.stacked-crooked.com/a/6c060d032bc53573