提升MSM仅处理内部转换

Question

我正在使用新的Boost 1.44.0 MSM库来生成状态机.在这个状态机中有两类事件class1和class2.class1事件可以由任一状态进行处理S1或S2同时class2事件只能通过状态进行处理S2.

特殊class1事件upgrade_req请求从州S1到州的升级S2.

我在Boost :: MSM中实现了如下:

// State S1 and S2 allow any class1 events
struct class1 {};
// Only state S2 allows class2 events
struct class2 {};

// an upgrade request is a class1 event that requests an upgrade to state 2
struct upgrade_req : public class1 {};

struct MyFSM : public msm::front::state_machine_def< MyFSM >
{
    /// State 1. Allows any class1 event
    struct S1 : public msm::front::state<>
    {
        /// functor says "processing event in State 1"
        struct ProcessEvent { /* ... */ };

        struct internal_transition_table : mpl::vector<
            //        Event   Action        Guard
            //       +-------+-------------+------------+
            Internal< class1, ProcessEvent, none >
        > {};
    }; // S1

    /// State 2. Allows any class1 or class2 events
    struct S2 : public msm::front::state<>
    {
        /// functor says "processing event in State 2"
        struct ProcessEvent { /* ... */ };

        struct internal_transition_table : mpl::vector<
            //        Event   Action        Guard
            //       +-------+-------------+------------+
            Internal< class1, ProcessEvent, none >,
            Internal< class2, ProcessEvent, none >
        > {};
    }; // S2

    /// everybody starts in state 1
    typedef S1 initial_state;

    /// send an error if a class2 event was received for state1
    struct SendError { /* ... */ };

    /// Send a response to the upgrade request
    struct SendUpgradeRsp { /* ... */ };

    /// functor returns true if the request to upgrade to state 2 is OK.
    struct VerifyUpgradeReq { /* ... */ };

    struct transition_table : mpl::vector<
        //  Start  Event         Next   Action           Guard
        // +------+-------------+------+----------------+------------------+
        Row< S1,   class1,       none,  none,            none,
        Row< S1,   class2,       S1,    SendError,       none >,
        Row< S1,   upgrade_req,  S2,    SendUpgradRsp,   VerifyUpgradeReq >,

        Row< S2,   class1,       none,  none,            none,
        Row< S2,   class2,       none,  none,            none >
    > {};
}; // MyFSM

我的问题是,当我按原样使用它时,upgrade_req事件永远不会被主要处理MyFSM::transition_table.它只由处理S1::internal_transition_table.

例如:

int main( int argc, char* argv[] )
{
    msm::back::state_machine< MyFSM > sm;
    sm.start();
    sm.process_event( class1() );
    sm.process_event( upgrade_req() ); 
    sm.process_event( class2() );
    return 0;
}

我希望这个输出是:

处理事件状态1.
升级请求确定.
在州2处理事件.

但是,我得到的是:

处理事件的状态1.
处理事件的状态1.
错误.在州1收到2级活动.

有人建议如何解决这个问题吗？

谢谢,PaulH

Answer 1

您的问题是内部转换的优先级高于转换表中定义的优先级.并且update_req是class1,内部转换器会触发.这实际上符合UML标准.MSM为您提供了第二个解决方案,您可以使用Row来定义S1的内部转换,其中none作为目标在transition_table内,而不是使用internal_transition_table.如果您在转换S1 + upgrade_reg - > S2之前定义它,它将具有较小的prio并且仅在不能考虑另一个时才会尝试.

如果你绝对需要internal_transition_table,那么你只能提供一个后卫来拒绝class1,如果它不是update_req.

HTH,Christophe Henry

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