Boost.MSM:通过连接伪状态退出正交区域

您可以使用一个计数器，该计数器将在每次进入联接状态时递增。当该计数器等于正交区域的数量时，连接状态之后的状态将被激活。

这可以手动完成，也可以以通用方式完成。下面我实现了一种通用方式，其中通过从模板JoinSM继承来将连接逻辑添加到子机Sub。

Sub有3个正交区域(在这个简单的例子中，每个区域仅由一个状态组成，即Orthogonal1、Orthogonal2和Orthogonal3)。所有这些正交状态都连接到Join状态，但是在Sub内没有指定从Join状态到Exit状态的直接连接。

该连接在JoinSM中实现。每次从Sub达到Join状态时，Waiting状态被激活，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，并激活向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

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